Converting MM of Water to Gallons per Minute

No.

No, there is not. mm of water is a measure of length while gallons (per min or otherwise) is a measure of volume. The form of "mm of water" is generally used in pressure measurements, like Column of Water etc. For example, a vertical 1000mm one inch and ten inch pipes will both read 1000mm of water column while their gallon content will be very different. And "gallons per minute" is another thing altogether. Incompatible units do not mix.

No - flow is measured in l/s , m³/h etc.

Are you working in US or Imperial gallon?

mmH₂O is a pressure.

Gallons per minute is a flowrate.

The only way these can be related to each other is in a device that measures a pressure differential and infers a flowrate from it. An orifice-based flowmeter is one such device.

Just to be contrary I shall say YES! (maybe)
But only in a fixed situation and by empirical means...E.G Measure it for several flow/pressure states, plot a graph and keep it for reference, or create a formula from the graph, (plenty of maths progs will do it for you). However periodic checking woul need to be carried out, as the slightes t change in conditions would modify the result.
Hmmm, maybe I mean 'no' after all?

Del

DO NOT LISTEN TO THE CAT!!! He'l make a minature mm and post a picture of it just to fool us.

It does not seem that the one asking the question is clear on the units..

BUT:

If we look at this like we are talking about volume not flow..

1 mm³ of water would equal about 0.0002642 gallons

or to turn it around 1 gallon would equal 3785.4 mm³ of water....

That said if we dwell further into this mass of assumptions and guesses and add flow back into the mix and keep the time units constant between the mm³ and the gallons then we would get;

1 mm³/min would be equivalent to 0.0002642 gal/min

1 Gal/min would be equivalent to 3785.4 mm³/min

Now all this would have made more sense if we just called mm³s ml's but I digress.

Duc

The <...gallon...> is a different size depending on location, of course; in the UK, for example, it is 4.54 litres and it is different elsewhere.