system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Can someone explain how units of measurements were decided upon, and why the math is perfect?

Is it just a coincidence that a cube measuring 1cm x 1cm x 1cm holds 1mL of water and has a mass of 1 gram?

Were all three units of measurement based on water?
gpt
It's not a coincidence, they were defined that way.

The meter was originally defined at 1/10,000,000 the distance between the equator and the north pole.

A liter is a unit of volume, defined as 1000 cm^(3), so 1mL = 1cm^(3) (one cubic centimeter). It is derived directly from the meter, and has nothing to do with water.

A gram was defined as the mass of one cubic centimeter of water at the melting point of water.