Bushels to Mass by Test Weight

The most important thing about a bushel of grain is that it is not a volume. The volume exists — 2,150.42 cubic inches, or 35.24 litres — but no elevator has measured it since the nineteenth century. What a contract means by a bushel is a legally defined WEIGHT, and it differs by crop: 56 lb for corn and rye, 60 lb for wheat and soybeans, 48 lb for barley, 32 lb for oats.

Those numbers are not arbitrary; they are the volume filled with each grain at the density it happened to have when the standards were written. Oats are light and chaffy and pack badly, so a volumetric bushel of them weighs barely half what corn does. The standards froze that in law, and the volume then became irrelevant. Converting is therefore one multiplication: 1000 bushels of corn is $1000 \times 56 \times 0.45359 = 25{,}401$ kg, or 25.40 t. Going the other way, a tonne of wheat is $1000/(60 \times 0.45359) = 36.74$ bushels — the figure every Canadian grain trader carries in their head.

The trap here is the phrase "test weight", which does double duty. The LEGAL test weight is the fixed number above, used to convert bushels to mass in every contract. The MEASURED test weight is what a particular load actually weighs per volumetric bushel, reported in lb/bu or kg/hL, and it is a grading factor — an indicator of how well the grain filled. A load of wheat measuring 56 lb/bu is light, will be discounted on grade, and is still converted at 60 lb/bu for the purposes of the contract. Using the measured figure in the conversion is a real and expensive mistake.

One more sequencing point. Legal test weights are defined at the contract moisture, so a wet lot must be shrunk to that moisture BEFORE it is converted to bushels. Converting first and shrinking afterward gives a different answer, and the difference is exactly the shrink on the water — small per bushel, substantial per truckload, and entirely avoidable by doing the two steps in the right order.