Weighing Suitcases in Hotel Rooms

Brilliant! That's a great idea. I can hang the scales off that; hang the suitcase off the scales.

Thank you!

Carry-on isn't weighed so why go thru the extra work putting items in pockets and then transferring to carry-on?

UPS, FedEx, DHL, and the other countertop shipping companies may become your friend. On your trip to the airport stop off at a counter with all of your luggage and goodies. Plan on shipping something back home with their service but you can now ask them to weigh your luggage. If the luggage is overweight then add some things to what you want to be shipped back home.

"... from coffee to washing powder...

Since it's hard to imagine pouring coffee or washing powder into the case one must assume they come in packs/packets...whatever.
I can't ever recall buying 1kg of something in a packet and getting even 1.1kg so 10 x 1 kg packs equals 10kg (and so on) and you should know the mass of the case...get yourself a calculator if the math becomes burdensome.
Some good wine or whiskey I could understand - but surely you have supermarkets where you live?

Tanks for the reply Sapling, great people are prepared to chip in time to help a stranger.

I'm in SE Asia. You'd be amazed. Often not so much that goods are unavailable but subject to import taxes and wildly expensive. Local products sometimes work well, sometimes not. Flour can be very expensive in rice-producing countries so that's often on the list for breadmaking. Even dried pasta is a luxury item in some places.

Yep, can add up the packets for a good rough guide. Doesn't work well for tins or jars though. Can weigh parts individually and that's what I've done for heavier allowances - but it's not as accurate as it could be. Ideally, I'd like to know, with some confidence, how heavy my suitcase is.

.... & there's some really good ideas here on that score!

First and foremost - I am not trying to be rude.
The number of expat's that come up with stuff like that here is amazing.
Which part of S.E Asia?
I live/work in Johor Bahru, Malaysia and have done projects in Indonesia, Thailand, Vietnam and Brunei - all SEA and my wife and I have never encountered this problem. I leave out Singapoorestan because it isn't a typical SEA country, and I usually commute to do my consultancy work there - it is, after all, a very expensive version of Sydney which is already a very expensive place.
Pasta a problem?
I do know that when I have picked up something in a can I do get all kinds of grief at airports because of their drug laws.
I had a glass of wine, or three, last night with two mates while watching the cricket in England. They both laughed and said that traveling with scales makes you look like the dumbest drug dealer around - one is head of Customs "Enforcement Unit" here and the other a police Superintendent - Narcotics. A question for you "How much do the scales weigh?"
BTW - Australian/New Zealand goods here in Johor Bahru are generally actually cheaper than in Australia.
BTW Part 2 - My wife added: "...maybe the list is more to keep him away from bars and girls than any real need - I've never encountered it..."

I wouldn't . My suitcase would be very light. If there was anything I wanted at my house, I would hire a commercial carrier.

Put a strap around the suitcase (length and width) and tighten it. Turn it onto the back face and hook the digital baggage scales under the strap at one corner of the front. Weigh, and repeat with the other front corner.

Add the two weights together.

"... Add the two weights together. ..."

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....'Add these two weights together...'...and write this value down.

Repeat the operation again weighing opposite corners of the bag lifted to an arbitrary height. Add the two weights together and write the new value down.

Continue doing this until it is possible to extrapolate reliably an upper timit on the sum of the two corner weights. If a sufficient range of arbitrary heights has been utilized, the actual weight (limited by the accuracy of the scale and operator) of the suitcase will be very close to half the upper limit.

Sorry, but I think that determining 2 weights in the manner I suggested is sufficiently accurate for practical purposes. Would you like to explain the inaccuracies which are resolved by your method?

My suggestion was kind of tongue in cheek, but there is a little truth in any joke, and in fact my improved method would b much more accurate because the upper limit of the sums of weights measured by lifting olposite corners to arbitrary heights would be twice the weight since lifting from a corner reaches a maximum when the entire suitcase leaves the ground.

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What I am pointing out is that lifting a corner of a typical suit case with a scale to an arbitrary height does not reliably allow you to measure half the weight of the suitcase. Moreover, lifting opposite corners with a scale to some arbitrary height does not reliably cancel the various errors introduced.

How high do you propose to lift each corner? The scale will vary between almost nothing, up to thr full weight depending on the height you lift each corner to. There is no obvious way of knowing exact how high to lift the ooposite to corners to sum to the correct weight.

Suitcases are not truly rigid (even the rigid style) and typically have convex sides. Moreover suitcases are not symetrical corner to corner with respect to places that might be hooked to hang and places that support weight resting on the carpet below. Most suitcases have soft or rounded corners such that the distance from center of mass will shift as the suitcase is lifted higher.

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Now, I'm pretty sure you were shooting from the hip with your suggestion. If you had experience with your proposed method, you probably would have brought that to light in the response to my comment. So why don't you try out the advice you were offering and see how variable and unreliable your suggestion is?

You still fail to make your point. We are not weighing 20kg suitcases to the nearest gram here. The principle I used applies equally to asymmetrical loads, so it really does not matter if the suitcase is asymmetrical. It should be obvious, even to you, that there is no need to lift the suitcase beyond the point at which the scales cease to increase in reading. Even with rounded edges, the change in fulcrum is unlikely to introduce a serious error.

If you wish to justify yourself then run away and design a suitcase which cannot be weighed by the method I propose. Or you could go back to designing collapsing bridges, which you might find simpler.

Ok"... that there is no need to lift the suitcase beyond the point at which the scales cease to increase in reading. ..."

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Well, duh! The scales cease to increase in reading when the entire suitcase is off the ground! That doesn't address the OP problem at all. In addition, using your method the weight will come out around twice the real weight. Your recommendation is folly.

So, it seems like I probably was correct that you have never tried this yourself and that you were just making a recommendations because you were so confident there could be no flaw in your reasoning,

Merely because you fail to understand that roundish soft sided suitcases with asymetrical attachment points for lifting will be so problematic to your recommended process as to render it useless, does not mean the problem goes away. The world does not disappear everytime you get dissatisfied and refuse to open your eyes.

Wake up, chum. The suitcase is lifted by one corner and supported by one corner. All the distance you need to lift is to make sure that the support is on only one corner, and not on any intervening ribs. Do you make life difficult for your wife as well?

Making things difficult? That's rich coming from someone who is telling his wife she can pack only half the weight she is actually alotted by the airline because he insists his absurd system of weighing is correct; a system that calculates weoght to be twice actual. .(..or at least that would be the case for someone who followed their own advice. Someone who adamantly denies the possibility of a flaw in a process he dreams up but has never tried is unlikely to be taking trips with his wife and may not even be ln speaking terms.)

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As a refresher, you say one must lift the scale attached to one corner of the bag until the indicated weight stops increasing, attach the scale to the other corner and once again lift until the indicated weight stops increasing, then sum those two values to get the weight.

So tell me, after you have lifted the corner of the bag using the scale and there is a reading a little more or a little less than half the weight of the bag, if you apply an additoknal upward force, wouldn't the reading on the scale increase?...right up until it is suspended only by the scale?

Don't weigh your wife's bags. Certainly don't weigh your wife. If you do, done share your calculation with her!

Let me refresh your knowledge of elementary statics. A beam is suspended on two fulcrum points in a horizontal line. The weight of the beam is W. The upward force on the beam from one fulcrum is F1, from the other F2. Then

F1 + F2 = W

(and please don't smart-*rse me by saying "Well actually they are vectors, so F1 + F2 = -W"). This is true whether or not the centre of mass of the beam is in the centre. F1 does not have to be equal to F2.

OK so far? Then we will move to the angle theta that the beam makes with the line between the fulcrums when one end of the beam is lifted (and please don't smart-*rse me by saying "Well actually they are fulcra")

Yeah and there is the problem. A suitcase is not well modeled by your simple beam. It is not typically very ridid and it is certanly not supported at just one single unmoving point.

Whem you attach a acale to one corner it will initially be resting on an area (not a point and not a line) the downward facing side. As you elevate the attached scale, that area will shift toward the other side. The more force you apply the further it will move over and the greater the scale reading.

When do you stop? Oh yeah, you said when the reading stops oncreasjng, which is when yhe weight is fully supported through the scale.

Ok, so I know i've asked you this twice before already, but I just cannot find when you have responded, so please humor me with a reaponse if we are to continue this discusaion:. Was I coreect in my early assumption that you have not actually done this yourself in real life, meaning this process you recommended and now are adantly defending as without flaw, is just something you made up on the spot? Well? That's what happened, right?

Go try it witth a suitcase and a scale. Make a video No one is going to believe you without a video demonstration as adamant as you are about this untested and poorly reasoned processnof yours.

Oh good, we are making progress. You accept my equation for a beam, so there is no further nonsense about my wife not being given the full allowance for her suitcase. However, we will continue to make progress slowly. The next stage for you is to accept that the mathematics are not altered if the fulcra are linear rather than point contact. Indeed they are barely altered if the fulcrum is a small area which changes fractionally when the beam is lifted off the other end.

OK so far?

Good, so we've digested that and can now move on to the real world suitcase. there are two important features to establish at this point. The weigh-each-end process makes two important assumptions:

1. The geometry of the suitcase is the same as each side is lifted.

2. The centre of mass does not change as one side or the other is lifted.

Now you suggest that a suitcase "is not typically very ridid", as if that is an important consideration. If distortion is a relevant feature, then you have to explain how the suitcase can assume one shape when one end is lifted and a completely different shape when the other end is lifted. I suggest instead that your understanding is even worse than your spell-checking.

The second point, a potential shift of the centre of mass, is of far more import. Obviously I am not suggesting this method when the sole content of the suitcase is a couple of tins of beans, but we are talking here about suitcases that have been stuffed full. The centre of mass is not going to shift any practical amount, whether the suitcase is rigid or not.

Again, OK so far? Do let me know if you need anything explaining again before I move on.

I'm stopping you at point 1. The geometry is not relaibly the same for each side lifted.

OK, what is it that changes in the geometry that does not also happen when the other end is lifted?

Many suitcases are soft sided. The contact patch will vary with local content. There may be a shoe in one corner and the other corner may not be packed such that there is a shor places symetrically in the other corner.

Also, suitcases are often not aymetrical even when semi rigid. The front is different than the back and the top os different than the bottom meaning no opposite corners are symetrical.

Look, as you elevate the auitcase and the contact patch moves to the opposite side, there will often be no clear point that might indicate when to cease lifting. Moreover, until the point that the bag is filly suspended by the scale, increasing lifting force will cause the indocated weoght to increase.

In short, the is no reliable indication (for even a perfectly symetrically loaded suitcase) of what height to raise the corner that might yield on sum with the other corner's measured weight the true weight of th suitcase.

You still have not answered my question in #29. Your assertion in #28 was that the suitcase somehow might end up in a different shape when lifted up at one end in relation to the shape when lifted up the other end. You are welcome to prove that such a difference, if it occurs at all, makes the method unreliable. Bear in mind in your answer that stuffed semirigid cases tend to become more rigid, not less.

Now to "Also, suitcases are often not aymetrical even when semi rigid. The front is different than the back and the top os different than the bottom meaning no opposite corners are symetrical." We have already discovered that the suitcase may be modelled by a volume enclosing a centre of mass. It may come as a surprise to you to discover that the model does not require symmetry. The centre of mass does not need to be in the centre.

I will leave you to ponder that for a while, and then we will explore the model further.

I'm not suggwating that your method is thrown off my a center of mass that isn't equidistant from your lift points

Among other things, i am pointing out that the fulcrum of the suitcase being lifted by corners is not a point nor even a line, but is an area that has irregular pressure across the contact surface. Furthermore the contact patch/fulcrum changes aize, location and pressure contours as the opposite corner is lifted.

You have not provided any reasonable deacription for when to stop lifting and take a measurement. You did say earlier juat lift until the scale reading no longer increases, but that of course is whem the entire suitecase is in the air..

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Just stop for a moment and lefts ignore the problem with the irregular contact patch working as the fulcrus. Let's go back to the rigid beam but instead of a straight beam with the fulcrum at the end, the beam has a convex lower surface such that as you lift, the contact point moves from the center out towards the other end. You have no knowledge of the exact curve other than in is convex and that the contact moves outward smoothly. If you are allowed to attach a scale to eother end and lift, but not allowed to lift the entire beam off the ground, how would you calculate the weight? Can you ahow your formula? How high would each end need to be lifted?

I think both of you have completely ignored the AHJ. No scale at the hotel, regardless of how it is used trumps the scale at the ticket counter. That scale at the ticket counter and the attendant reading it has AHJ status. Any excess weight perceived by that scale and attendant will require paying for extra baggage or discarding the baggage. Go to a commercial shipping company or even a post office to ship the things you don't need if your flight lands safely somewhere not your destination.

I'll give you a GA for that, but my habit is to answer the original question, which was how to do it in a hotel room.

You are exactly right redfred. The airline has the last word on weight and the best we might do ahead of time to prepare is have a reasonably accurate scale and process and hope the airline does too.

This is also an engineering blog, so when someone suggests a solution that will not reliably deliver the claimed results, then I feel obligated to point out the problem.

Specifically when someone suggests accurate weights of various typical luggage pieces can be determined by lifting two opposite corners to an arbitrary height with a hanging scale and adding together the weights read at those arbitrary heights, I feel compelled to voice my disagreement.

You're missing my second point. If one has things that they don't need to go with themselves on the plane then don't take them. Ship them to where one wants them to be. Bring only the things one has to have with them, regardless of weight limitations and possible fee avoidance.

No. i understand that point and it is a good one.

Please undrrstand, the reason I am commenting on the 'lift opposite corners' process is not because I think it is a superior solution. I don't even think it is a workable solution.

I think it would be wrong to let a suggestion like that go unchallenged on cr4.

I get it that one of the ways communicated to you would not work and would induce significant errors. I also get that phph believes the technique he wants to communicate should work accurately.

I profess that this is all a moot point. The original premise is a foolish idea in the first place. Shipping costs are not that exorbitant. Maximizing the load this airplane has to carry makes it more likely for somebody's luggage to be lost. The OP should be trying to make anyone they deal with about air travel easier and not trying to game the system. Loose the scale. Loose the bracer bar/fulcrum. Pack only what you need and ship the rest. I don't want to be one of the ones waiting behind the OP as they claim their luggage has to be underweight, particularly if they have to unpack, discard and repack as others wait. Be mindful of others and not so selfish.

I still wonder how heavy a scale that can weigh 32kg would be - especially to cart around with you.

3.2 ounces

It is not the greatest discovery since Einstein to work out that a contact patch, as "an area that has irregular pressure across the contact surface. " can be modelled as an area with a centre of pressure, in just the same way as a suitcase can be modelled as an volume with a centre of mass. With this in mind let us look at the figure.

In (1) the beam is symmetrical.F1 + F2 = W and also F1 = F2

In (2) F3 + F4 = W, but F3 and F4 are not equal

The interesting thing is to compare (1) with ((3). In (3) F5 + F6 = W, and the more you look at it the more obvious is the relation F1 = F2 = F5 = F6 = W/2.

I think that is enough of this heady stuff for now. We will come to the curved beam shortly.

Yes, we can agree these things are true for a rigid beam supported on either end on pivots that allow only force in one direction, equaldistant from the ceter of mass. This is not sufficiently similar to the suitcase with varying lift points and dynamic spread fulcrum.

Also, you may assume the uneven pressure has a center of pressure within the area, but where? Also it will not reliably be the same point when lifted a little higher or from the other corner.

You are mistaken again. The centre of mass does not have to be equidistant from the fulcrum points. It is, of course, important that the only lifting forces are vertically upwards.

ItIt doesn't have to be equidistant, but you'd have to know something like the distances and the distribution of weight about the fulcrum at that particular lift height, which you don't.

Remember you have just one hanging scale. The amount of nonrigid bag laying on the other side of the pseudofulcrum at any arbitrary lift height is unknowable to you. Perhaps in this semirigid suitcase some of that weight on the other side of the pseudofulcrum is offsetting the weight closer to you, or maybe it isn't you don't know. You've been modeling this as a rigid beam.

You don't even know how much weight is resting on the floor. These aren't friction free pivots only transfering weight up or down. You could easily be balancing the weight on the corner with the right arrangment.

The possibility for large error introduced in multiple ways approaches a certainty. Your oversimplification of a rigid beam supported on either end is the thing keeping you confused.

Some people do use duffle bags. But aside from that there are numerous other types of luggage this would not work for.

Even on hard luggage there is not typocally a hard sharp pivot certainly not directly below where one might attach a point to hang the bag. Ever tried to tighten a strap around the corner to corner length of a slippery box with rounded corners? Good luck getting it at all, much less repeatably similar.

As descrobed, the process will not even yeild consiatent results on the same piece of luggage. How high is high enough to lift? Where does this make the pivot in relation to the unattached opposite corner to be weighed next?

You are thinking as if the suitcase were indeed the somplified model. The model is wrong and in this case it is not useful as applied.

You brought up the wife initially. It is fair gamr to respond to something you initiated. The wife remains in play until such time as you admit it was mistake and retract your initial comment bringing the wife into play.

In the real world the contact patch is am area. If you were to model it to a 2d cross section, it would appear as a line. Depending on the contents and arrangement in the suitcase the amount of support at each portion of the area in real life (and so each point along your line in a 2d cross section model) will vary. It will not reliably be at the center.

My wife would not suffer the loss of half her luggage allowance, which is what you imply. Do you burden your own wife with similar implausibilities?

I am coming to the point of real-world contact patches. As a snippet to come, real world suitcases may also be modelled by a concentrated mass contained at some point within a rigid (or semi-rigid) volume.

Still looking?

40+ answers...some smart-arsed (Aussie version of smart-donkey...never got the yank translation of "arsch" to refer to some animal)

wow.

A simple question - needs a simple answer...but alas it was a multiplex of conundrums.

You can't afford a hotel that has a bath scale? Why does your company allow you to fly airlines with such high baggage limits? Bath scale minus 10% for safety...weigh yourself first...perchance? And remember how fat you are...
Wife's list - FedEx back...when she sees the bill the list will disappear.
No-one answered but as near as I can find on google is a handheld scale that can measure 35kg - 32 is useless because you wouldn't know if you passed the limit - is 2.1kg...a factor perchance?

"...No-one answered ..."

I answered. A 40 kg scale accurate to 10 g weighs less than 100 g.

Where pray tell, can those scales be had?....us poor fishermen ask

Follow the link in #44. ... the response to your post with the original inquiry.

I saw one with the suitcases at Walley World last week.

Hi Sapling,

Bath scales sadly neither universal nor very accurate. I did before try that but results (where I could get them) varied wildly.

I get high baggage limits because I'm flying long distance and usually in Business. I'm also a high-rated frequent flyer so get /extra/ baggage or weight. Usually I take one suitcase that's at about 60% and another that's empty. I fill them with as much stuff that's either much, much cheaper in the UK, or rare outside (don't get me started on Marmite) or is a favorite product. That way I save a fair bit of money. The nearer I can get to the weight limit, the more I'm saving. But, like the best jeopardy games, go over and you pay!

My current hanging electronic scale has proven really accurate, is very light, and drops into my hand luggage. There's lots of them on Amazon.

Everyone - Thank You!

Really grateful for all the contributions. @SolarEagle, I've ordered an over-the-door hanger I found on Amazon. Looks robust but is coming from America so it will take a while. @phph001, intrigued by your suggestions (and the debate with Truth is not a compromise) I will experiment with weighing in that manner and see how close I can come to a hang weight.

Thanks again all, as ever, I've learned stuff and gained loads of ideas.

Been traveling quite extensively for the past 9 months and experienced the same issues with overweight language... pack close to the limits.

I stopped at the big box store, and picked this up...

saved me a lot of time when I pack before I go to the airport, no worries now when I check my bags...

After you pack your bags, just set the type of weight... loop and hook on the handle, and lift. Takes about 5 seconds. I then pack it in the outside zipper pocket on the luggage and secure it by zip tie it shut.

I’m sure their available on Amazon and eBay also.

Sorry,... after rereading, you were just looking for a hanger to assist.