1l of (4°C) water weighs 1kg. 1kg (of anything) is 1000g. 1g of water is 1cm³. Stack 1000 1cm³ blocks to get a 10m high column. This column exerts 100kPa of pressure on its base. 1N would accelerate it by 1m/s every second. And to heat it by 1°C requires 1kcal.

See, kcal is not a metric unit. But noone cares, because its relationship to other units still contains meaningfull information about physical reality. In metric you get knowledge for free. Meanwhile if you convert feet to miles, you get 5,280, for some reason.