Grain shrinkage: where weight goes between field and sale

The fields weighed 1,000 tonnes in August. The sales invoices total 952 tonnes by June. Somewhere, 48 tonnes of wheat — call it £9,000 or so at recent-seasons prices — has apparently evaporated, and someone around the kitchen table wants to know where it went.

The honest answer, most years, is that nearly all of it really did evaporate. Shrinkage of 3–5% between field weight and sold weight is normal, and almost all of it is water. But "normal" and "provable" are different things, and the difference between them is per-load records. A farm that recorded weight and moisture for every load can turn that 48 tonnes into arithmetic in ten minutes. A farm that didn't has an accusation looking for a target.

Where the weight actually goes

Moisture: the big one

Water is weight, and drying removes it. The formula is simple enough to do on the shed door:

dried weight = wet weight x (100 - wet moisture %) / (100 - dry moisture %)

Worked example: 100t of wheat comes off the field at 18% and is dried to 14.5% for storage. Dried weight = 100 x 82 / 85.5 = 95.9t. That's a 4.1% weight loss — four tonnes of water up the drier stack, entirely legitimate and entirely invisible unless the wet weight and moisture were recorded on the way in. Our grain drying calculator does the sums per load or per shed if you'd rather not.

Two things people miss. First, the loss compounds with the drying bill — you pay £2–£3.50/t per point to remove the water, then sell fewer tonnes as well; the drying costs guide covers the full damage. Second, grain keeps losing moisture slowly in a well-ventilated store, so even undried grain sold in spring can weigh slightly less than it did in August.

Screenings and dust

Cleaning, drying and every transfer between shed and lorry shakes out small grains, chaff and dust. Individually trivial; across a season, typically a fraction of a percent. If grain goes over a cleaner for a premium market, screenings become a visible heap with a weight of their own — record it and the "loss" explains itself.

Handling

Spillage at the pit, the odd bucketful left in a corner, grain trodden into the floor, the auger's worth that never quite comes out. Fractions of a percent again, but real.

Record gaps pretending to be shrinkage

This is the category that isn't physics. Loads that never got weighed because harvest was flat out. A trailer that went to the wrong shed. Field weights estimated off the combine monitor rather than a bridge. A ticket book that got wet. None of it is theft and none of it is evaporation — it's just missing data, and at reconciliation time it's indistinguishable from either.

What's normal and what isn't

Field-to-sale shrink	Reading
3–5%	Normal for grain harvested damp and dried — mostly water, plus screenings and handling
1–3%	Normal for a dry harvest with little drying
Persistently above ~6%	Worth investigating — something beyond moisture is going on

The word doing the work is persistently. Any single season can be odd. But an extra 2% every year, on top of what the moisture arithmetic explains, has a short list of causes:

• A drifting weighbridge. A bridge reading heavy at harvest (or the buyer's reading light) builds a phantom loss into every load. Annual checks catch it — see weighbridge calibration.
• Missing tickets. Loads sold but never recorded as leaving, or harvested but never weighed in.
• A light-fingered figure. Rare, unpleasant, and the one everyone fears — which is precisely why you want the other explanations eliminated on paper before anything is said out loud.

Turning shrinkage into arithmetic

The whole subject changes character with one habit: a weight and a moisture reading for every load, in and out.

In practice that means each incoming load gets weighed and its moisture recorded against field and shed; each outgoing load gets your loading weight, the buyer's intake weight, and the destination. From those records, the year-end reconciliation stops being a shrug:

1,000t harvested at an average 17.2%, dried to 14.5% — the formula says 968t of dry grain, so 32 of the 48 missing tonnes are water before anyone's looked further. Screenings weighed 6t. Buyer's intake weights ran 0.3% under farm weights all season — 3t, and a question for the calibration company. The remaining 7t sits within handling losses and rounding across 300-odd loads. Done: 48 tonnes accounted for, nobody accused of anything.

That's the real value of per-load records. Not the recording itself, but what it does to the conversation in June — "shrinkage" stops being a suspicion and becomes a column that adds up. It's also, not incidentally, the evidence that settles weight disputes with buyers and hauliers, where the same missing half-tonnes otherwise vanish unchallenged.

Frequently Asked Questions

What is normal grain shrinkage?

Between field weight and sold weight, 3–5% total shrink is normal for grain harvested damp and dried for storage, and 1–3% in a dry year with little drying. Most of it is water removed in drying, with screenings, dust and handling losses making up small fractions of a percent each.

How much weight does grain lose when dried?

Dried weight equals wet weight multiplied by (100 minus wet moisture) divided by (100 minus dry moisture). Drying wheat from 18% to 14.5% loses about 4.1% of the weight — 100 tonnes wet becomes roughly 95.9 tonnes dry. The water removed is real, saleable weight gone.

Why don't my grain sales match my harvest weights?

Usually moisture: grain is weighed off the field wet and sold dry. Add screenings, handling losses and any loads that weren't weighed or recorded, and a 3–5% gap is expected. Per-load records of weight and moisture let you reconcile the difference exactly instead of guessing.

When should I worry about grain shrinkage?

When the gap persistently exceeds what the moisture arithmetic explains — as a rough guide, above 6% field-to-sale, year after year. Common culprits are a weighbridge drifting out of calibration, loads leaving without tickets, or field weights that were estimates rather than weighings. Rule those out with records before suspecting anything worse.

Does grain lose weight in storage?

Slightly, yes. Grain continues to dry in a ventilated store, so tonnage sold in spring can be marginally below the weight that went in, even without a drier involved. It's another reason to record moisture at intake — the loss is explainable if you know what the grain went in at.