Grain Weight at a New Moisture

One sentence carries this entire page: the dry matter does not change when the water leaves. A tonne of wheat at 18% moisture holds 820 kg of dry matter and 180 kg of water. Dry it to 14% and the 820 kg is still 820 kg — it is now 86% of a smaller total, so the total is $820/0.86 = 953.5$ kg. Everything else here is that arithmetic rearranged.

The formula as the trade writes it is $W_2 = W_1 (100 - M_1)/(100 - M_2)$, and the two brackets are the dry matter shares before and after. Taking 30 tonnes of canola from 12% to the 8% straight grade gives $30 \times 88/92 = 28.70$ t. The 1.30 t difference is the shrink, and it is not a fee — it is water that has left the load and is not there to be weighed.

Two mistakes account for nearly all the errors. The first is confusing moisture points with percentage of weight: going from 20% to 15% is five points of moisture but only a 5.88% loss of weight, because the denominator moved too. Anyone who deducts 5% instead of 5.88% is short by more than a tenth of a percent of the load, every load. The second is dry basis. Laboratories and the feed industry sometimes express moisture as a share of the DRY matter rather than the wet weight, and 20% dry basis is 16.7% wet basis. Every grain contract on earth is wet basis; if a number came from a lab, confirm which one it is.

Worth separating from all of this is handling shrink, which is a different animal. An elevator's shrink factor typically exceeds the moisture arithmetic by half a point to a point and a half, and that excess covers dust, broken kernels, invisible loss and the elevator's own margin. It is a commercial term, negotiable, and it appears on the ticket alongside the moisture shrink rather than inside it.