A millimetre of water weighs nothing, because a millimetre is a measurement in one dimension - a measurement of length. 3 dimensions are needed to describe a real quantity, with mass. A millilitre of water, on the other hand, equivalent to 1cm3, has a mass of exactly a gram. This is because the properties of water are among the principle constants upon which the metric system is based. A cubic millimetre of water has a mass of 0.001g.
It becomes denser and denser until that 1 sq millimeter may to weigh as much as one ton.
One millimeter is 0.393701 inches.
1 litre.
One once
100 US gallons of water is about 835 pounds.
2 liters
834.5 pounds.
One millimeter is MUCH wider than a human hair. About 20 human hairs equals 1 millimeter.
150 milliliters of pure water weigh 150 grams.
At 17oC one gallon of water weighs 4.536kg.
One cubic centimeter of water would fit into that cup, and it would weigh 1 gram.
I litre of water weighs one kilogram on year and would weigh 0.1 kilograms.