Is that US gallons or IMP gallons?

How do you all get by with this system when real accuracy is needed?

I was telling my students the other day that 1 Liter of water, is exactly 10 cubed centimeters in volume, and exactly 1 Kilogram in weight.

This is true no matter where in the world you are, and you do not need a calculator to find out what % of a liter is.