The metric system is all based around 1 cubic centimetre of
water under normal conditions. From this, we can derive length,
volume and mass units ie:
1 cubic centimetre of water has the volume of 1 millilitre.
1 cubic centimetre of water has the mass of 1 gram.
1 cubic centimetre of water measures 1 centimetre, so 1000 in a
row would measure 1 metre.