Test Weight, Explained
Test weight measures grain density — pounds per measured bushel — and it's a quality gate, not a yield number. Here's what moves it, when discounts start, and what it does and doesn't mean.
What test weight is
Test weight is the density of grain — the weight of the grain that fits in a measured volume, expressed as pounds per bushel. The standards are 56 lb/bu for corn and 60 lb/bu for soybeans.
It's a quality measure, not a quantity measure: you're paid on scale weight, but test weight determines the grade — No. 2 yellow corn (the default trading standard) requires 54 lb/bu or better; No. 1 requires 56.
When it costs you money
Buyers discount below their grade cutoff — commonly a few cents per bushel per pound under 54 on corn, steepening as it drops (every elevator's schedule differs). Low-test-weight grain also stores less forgivingly: lighter, less mature kernels are more prone to breakage and spoilage, so it's the grain to move first, not the grain to bury in the back bin.
What moves test weight
- Anything that ends grain fill early: frost before maturity, late-season drought or heat, disease pressure (tar spot, gray leaf spot years show it).
- Moisture at harvest: wet corn tests lighter; test weight typically rises about a quarter to half a pound per point of moisture removed in drying — so 58-pound dry corn may have crossed the pit at 55.
- Hybrid genetics: some hybrids simply test heavier; it's a stable trait worth knowing per hybrid.
- Handling damage: cracked kernels and fines drop it.
What it doesn't mean
Test weight is a weak predictor of feed value — pounds are pounds, and studies keep showing similar feeding performance until test weight gets severely low. And it isn't a yield measure: a field can yield huge with mediocre test weight, or the reverse. Treat it as what it is — a grading number that controls discounts and storability — and manage the marketing accordingly: blend, feed, or move light corn early rather than paying the discount on your best bushels.
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