The answer depends on whether you want to measure the mass or the height of a stack of the books. Furthermore, maths textbooks come in all shapes and sizes.
Kilograms
It would be more appropriate to measure 5 math textbooks in grams or kilograms, as they are smaller and more suitable units for measuring the mass of books. Milligrams would be too small a unit for this measurement.
milliNewtons. A gram or kilogram is a measure of mass, not weight.
Measure what? Their mass, length, volume?
KILOGRAM IS THE BASE UNIT FOR MASS yards are the best unit for math
The international (SI) unit of mass is the kilogram.
The same unit as you use to measure any mass. The SI unit for mass is the kilogram.
The standard unit to measure mass is kilograms.
Strawberries would be measured in grams or ounces.
The official SI unit for mass is the kilogram.
You would use the unit of measure called "kilograms" to measure the mass of an elephant.