Twelve inches in a foot, sixteen ounces in a pound, four quarts in a gallon. None of those is a power of ten, and that is exactly why the customary system is the harder half of the standard — free printable sheets with an answer key.
If they get stuck
The answer key prints on a separate page.
Metric conversion is a point moving: 3 m is 300 cm because the factor is a hundred and every metric factor is a power of ten. The customary ladders have nothing to lean on — 12, 3, 16, 2 and 4 — so each one is a real multiplication or division a child has to know and carry out. The standard names both systems, and a site that prints only the metric half is doing only the easy one.
Three ladders, each on its own sheet. Length runs inches to feet to yards; weight runs ounces to pounds; capacity runs cups to pints to quarts to gallons, which is the one children mix up because three of its four steps are doubling and the last is not.
204 in = ? ft