Length, volume and mass in metric units: 30 mm = ___ cm, 12,000 mL = ___ L, 7 kg = ___ g. The metric system is built on powers of ten, so every conversion here is multiplying or dividing by 10, 100 or 1,000.
That is the whole reason the metric system is taught this way, and it is also why these sheets pair well with place value work. Moving between mm and m is the same operation as moving a digit three places, and a student who sees that has the system rather than a table to memorise.
10 mm in a cm, 100 cm in a m, 1,000 m in a km, 1,000 mm in a m, 1,000 mL in a L, and 1,000 g in a kg.
Count the zeros. Every factor here is 10, 100 or 1,000, so converting is moving the decimal point one, two or three places - right when going to a smaller unit, left when going to a larger one.
Because the problems are built from their answers and multiplied up, so nothing divides unevenly. 250 cm = 2.5 m is a genuine conversion and a decimals question; it belongs on a decimals sheet.
Fourth and fifth grade. It usually arrives once multiplying and dividing by powers of ten is secure, because that is all a metric conversion is.