Standard Meter Length

The original idea was that one meter = 10^-7 of the arc distance from earth's equator to the pole. That may have been arbitrary, but somebody had to pick something. This is perhaps better than an inch being three barleycorns, or the width of some king's thumb.

A standard is needed

From Mr Wiki - Since 1983, it is defined as the length of the path travelled by light in vacuum in ¹⁄_299,792,458 of a second

or the length of the wave of a specific frequency

Our surveying system started with the unit "Cape feet" which is not equal to an English feet.

The imperial and US Gallon is another confusing example.

Hendrik,

The definition referred is more recent when scientists could be able to measure speed of light accurately. It was an effort to compare the existing standard length of meter with some reliable fixed value. The length of standard meter was decided much before this accurate measurement. If this standard length would have been decided after this accurate measurement of speed of light, then the definition would have been "length of path travelled by light in vacuum in 1/300,000 second". Similarly, if the length of second was not decided earlier then the definition of second would have been the time needed for a cesium-133 atom to perform 10 billion complete oscillations instead of "The time needed for a cesium-133 atom to perform 9,192,631,770 complete oscillations"

I remember the the definition of meter studied during my school days that it is length of a rod kept in a French laboratory at 20 deg C. I think this may be a better answer for OP."What's reason for this Standard length, why not less or more than this length of a meter in (MKS) . why we ask them one Meter ( 100) cm. When metric system of measurement was formulated, basic units for length, wight and time was decided to be called as meter, gram and second. Centi, deci, kilo etc were preceded to to it express lower/higher denominations.

All measurement systems are entirely arbitary.
They are created for convenience. Originally they were different in various countries but as travel and business became more widespread it was necessary to create standards for reference.
These have been adjusted over the years to be more accurately reproducible, however the bottom line is they are still completely arbitary and occaisionally need adjusting to fit in with the real world, e.g Leap years.
Del

The reason for the "standard" Length is so that measurements may agree. Without standards, nothing can be matched reliably or repeatably. This plays hell with interchangeable and complex parts.

Others have given reasons why this particluar "standard" was chosen.

Milo