Specific weight: what kg/hl means and why buyers care
Specific weight is grain density in kg/hl, measured with a chondrometer. Typical minimums for wheat, barley and oats, what lowers it, and how claims work.
· 7 min
Specific weight is the weight of grain that fits in a fixed volume, expressed in kilograms per hectolitre — kg/hl. It's measured with a chondrometer: a standard container is filled from a standard height, struck off level, and weighed. Feed wheat at 72.5 kg/hl or better is the common contract benchmark; a shrivelled drought-year sample might struggle to make 68.
It's sometimes called bushel weight, which is the same idea in imperial clothes — 1 kg/hl is roughly 0.777 lb per bushel. Same measurement, different units, identical arguments at the intake.
Why buyers care about a density figure
Two reasons, one about the grain and one about the lorry.
The grain reason: specific weight is a rough proxy for how well the grain filled. Plump, well-filled grain packs densely; shrivelled, stressed grain doesn't. For a miller that correlates — loosely — with flour extraction; for a feed compounder, with energy content per tonne. It's an imperfect proxy and everyone in the trade knows it, but it's fast, cheap, repeatable at every intake in the country, and it's been in contracts longer than anyone now writing them has been alive.
The lorry reason is blunter: haulage sells space as well as payload. Low specific weight grain takes more cubic metres per tonne, and at the bottom end a bulker can cube out — hit its volume limit before its weight limit — so every load moves fewer tonnes for the same haulage cost. Buyers price that in.
Neither reason requires the buyer to be right about your particular sample's feed value. The number is in the contract, so the number is what gets settled on.
Typical contract minimums
As a rough guide — individual contracts vary, and premium markets set their own terms:
| Grain | Typical minimum (kg/hl) |
|---|---|
| Feed wheat | 72.5 |
| Milling wheat | 76 |
| Feed barley | 62.5–63 |
| Oats | 50 |
Milling wheat's higher bar is part of the package of milling wheat specs alongside protein and Hagberg — and with milling premiums commonly running £20–£60/t over feed, a sample that fails on specific weight alone is an expensive near-miss. The specific weight converter moves between kg/hl and lb/bu if a spec arrives in the wrong units.
What drops specific weight — and what doesn't fix it
The damage is done in the field, mostly at grain fill:
- Drought or heat during grain fill. The crop builds grain sites it can't fill; the grain ends up small and shrivelled. This is the classic cause of a low specific weight year.
- Disease late in the season. Anything that kills the green leaf early cuts grain fill short with the same result.
- Sprouting and weathering. A wet harvest that starts grains sprouting reduces density, usually with a Hagberg problem arriving alongside.
- Admixture and screenings. Chaff, small grains and rubbish in the sample pack badly and drag the reading down.
What fixes it after harvest: almost nothing. Specific weight is a property of the grain itself, and no amount of drying, moving or wishful thinking plumps a shrivelled sample back up. The one honest exception is cleaning — taking out screenings and admixture lifts the reading marginally, sometimes a point or so, which matters only when a sample is sat just under a threshold. Whether cleaning pays depends on the deduction it avoids versus the cost and the weight removed.
Worth knowing: the sample is the sample. A load's specific weight is decided by which grain goes in the lorry, so if one shed's wheat is known to be light, blending decisions at loading matter more than anything done at the store. That starts with actually testing what's in each shed — see grain sampling and testing.
How claims for low specific weight work
If a load tests under the contract minimum, the buyer generally has two options: reject it, or accept it with a price allowance (a claim). In general terms, allowances scale with the shortfall — a set deduction per tonne for each kg/hl below the minimum, down to a floor below which rejection is standard. As a rough guide, deductions of around £1/t per kg/hl below spec are a common shape for feed wheat, but the schedule is whatever your contract says, and contracts differ.
A worked scenario: 29 tonnes of feed wheat tests at 70.5 kg/hl against a 72.5 minimum. At a typical allowance that's a claim in the region of £60 on the load — annoying rather than ruinous. The same wheat turned away from a milling contract and re-sold as feed loses the £20–£60/t premium on the whole load, which is a different order of pain. Knowing your specific weight before the lorry leaves — a chondrometer costs less than one rejected load's haulage — is what keeps the second scenario theoretical.
Frequently Asked Questions
What is a good specific weight for wheat?
Anything comfortably over 76 kg/hl is a good sample — it clears the typical milling minimum and leaves margin for sampling variation. Feed contracts commonly ask 72.5 kg/hl, and a well-filled crop in a decent year sits in the high 70s without difficulty.
What is the difference between specific weight and bushel weight?
They measure the same thing — grain density — in different units. Specific weight is metric (kg per hectolitre); bushel weight is imperial (pounds per bushel), and 1 kg/hl is about 0.777 lb/bu. UK contracts use kg/hl.
Can you improve specific weight after harvest?
Not meaningfully. Specific weight is set by grain fill in the field, and nothing in the store plumps shrivelled grain. Cleaning out screenings and admixture can lift a sample marginally — occasionally enough to clear a threshold — but that's the limit.
Why is the specific weight minimum for oats so much lower than wheat?
Oats carry a husk, which packs far less densely than the naked wheat grain, so around 50 kg/hl is the normal contract level rather than a sign of poor grain. Comparing kg/hl across different cereals doesn't mean much; comparing within a crop does.
Does high moisture affect specific weight?
Yes — wetter grain generally reads lower, and readings move as grain dries, which is one reason intake figures can differ from on-farm tests taken at the pit. Test at, or corrected to, a consistent moisture if you're comparing samples fairly.
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