Inches, feet and yards; ounces and pounds; cups, pints, quarts and gallons. 48 inches = ___ feet, 8 pounds = ___ ounces, 36 quarts = ___ gallons.
Customary units are harder than metric for one reason: the factors are all different and none of them is ten. Twelve inches in a foot, three feet in a yard, sixteen ounces in a pound, four quarts in a gallon. There is no pattern to fall back on, which is why these have to be practised rather than worked out.
12 inches in a foot, 3 feet in a yard, 36 inches in a yard, 16 ounces in a pound, 2 cups in a pint, 2 pints in a quart, 4 quarts in a gallon, and the combinations of those.
Because every factor is different. Metric is always a power of ten; customary asks a student to remember twelve, three, sixteen, two and four, and to know which applies to which pair of units.
These sheets use ounces as weight only - 16 ounces in a pound. Fluid ounces are a separate unit that happens to share the name, and mixing the two in one problem set would be a trap rather than a lesson.
Fourth and fifth grade, usually alongside or just after metric conversions.