How much grain fits in your shed?

The sum is short: floor area × average grain depth × bulk density = tonnes. A 24m × 12m bay filled level to 2.5m holds about 550 tonnes of wheat. The catch is in the words "average depth" and "about" — heaps aren't level, bulk density varies crop to crop and load to load, and the difference between the shed you think you have and the shed you actually have is routinely 10% or more. On an 800-tonne store that's 80 tonnes: nearly three artic loads that either don't exist when the merchant's lorries arrive, or sit unsold because nobody believed they were there.

The arithmetic

Three numbers:

1. Floor area — length × width of the grain-covered floor, in metres.
2. Average depth — the honest average, not the depth at the deepest point.
3. Bulk density — tonnes per cubic metre for the crop, as stored.

Multiply them. That's it. The skill is in getting the second and third numbers right.

Bulk density: the crop matters a lot

Approximate as-stored figures for the common UK crops:

Crop	Bulk density (t/m³)
Wheat	0.75–0.78
Beans	0.80–0.83
Barley	0.62–0.70
OSR	0.65–0.68
Oats	0.50–0.55

Two things jump out. Oats need roughly half again the space of wheat for the same tonnage — a shed that takes 550t of wheat takes maybe 380t of oats. And barley's range is wide: a bold sample of spring barley and a thin, screenings-heavy feed sample can differ by 10% in density, which is 10% straight off your capacity estimate. Specific weight from your intake tests is the clue — a low specific weight year means the shed holds fewer tonnes than usual.

Why heaps flatter you

Grain doesn't stack vertically. Tipped loose, cereals settle at an angle of repose around 25–28°, so a free-standing heap is a pyramid with long shallow sides — and a pyramid holds a third of the volume of the box it sits in. The visual effect is cruel: the peak looks impressive from the shed door while most of the floor near the walls carries a few hundred millimetres of grain.

That's why eyeball estimates of heaps run high. The eye reads the peak height as if it were the average depth, and on a big loose heap that can overstate tonnage badly.

Walls change everything. Grain walling lets you fill level, or nearly level, so the average depth approaches the wall height and the same floor holds far more. A 24m × 12m bay:

• Loose conical heap, no walls, peaked at 4m: the heap only covers part of the floor and averages perhaps a metre of depth over what it does cover — maybe 250–300t of wheat, despite the impressive peak.
• Walled to 3m, filled level at 2.5m average: 24 × 12 × 2.5 = 720 m³ × 0.76 = about 547 tonnes.

Same shed, roughly double the grain. It's also why "the shed's nearly full" means very little without knowing how it was filled.

Our grain store capacity calculator does the sum for level fills and heaped profiles per crop, if you'd rather not keep the angle-of-repose trigonometry in your head.

The estimate is a starting point, not a stock figure

Capacity arithmetic tells you what a shed could hold. It's the right tool for planning — will this year's wheat area fit, which bay takes the malting barley, do we need the co-op space this season?

It's the wrong tool for answering "how much is left to sell?" Depth is uneven, density varies through the heap, and every estimate inherits every previous estimate's error. Farms that reconcile eyeball stock figures against actual weighed-out tonnage at the end of a season are commonly 10%+ adrift, and the error compounds when part-loads leave all winter.

The only running total that stays true is weighed loads in minus weighed loads out. If there's no weighbridge on the farm, there are still workable ways to weigh grain — but some weight record per load beats the best-calibrated eyeball. The capacity sum tells you the shed can hold 550 tonnes; the load records tell you it currently holds 512.

Frequently Asked Questions

How do you calculate grain store capacity?

Multiply floor area (m²) by average grain depth (m) by the crop's bulk density (t/m³). A 24m × 12m bay filled level to 2.5m holds about 720 m³, which at wheat's 0.75–0.78 t/m³ is roughly 540–560 tonnes. Use the honest average depth, not the peak height.

How many tonnes of wheat per cubic metre?

Wheat stores at roughly 0.75–0.78 tonnes per cubic metre, depending on variety, moisture and how bold the sample is. Barley is lighter at 0.62–0.70, oats lighter still at 0.50–0.55, while beans are denser at 0.80–0.83. A low specific weight year means fewer tonnes in the same shed.

Why does a heaped grain store hold less than it looks?

Because loose grain settles at an angle of repose of about 25–28°, a free-standing heap is a shallow-sided cone — most of the floor carries far less depth than the peak suggests, and a cone holds only a third of the volume of the box around it. Grain walling that allows a level fill can roughly double what the same floor holds.

How accurate are eyeball estimates of grain in a shed?

Commonly 10% or more out, which is an 80-tonne error on an 800-tonne shed — nearly three artic loads. Capacity arithmetic is fine for planning space, but the only accurate running stock figure comes from weighing loads in and out and keeping the tally per store.