What this calculator does
A round grain bin holds a cylinder of grain, so the volume is π times the radius squared times the height of the grain. Converting to bushels uses 0.8036 bushels per cubic foot, since a US bushel is 1.2445 cubic feet.
Radius is squared, so it dominates. A bin of twice the radius holds four times as much at the same grain depth, which is why capacity rises so steeply with bin diameter. Going from a 20 foot to a 40 foot diameter bin takes capacity from about 5,000 bushels to about 20,000 at the same 20 foot depth.
The formula
The volume is π multiplied by the radius squared and by the grain height, giving cubic feet. Multiplying by 0.8036 converts to bushels. The calculation covers the cylindrical portion only, so grain peaked above the eave or held in the cone of a hopper bottom is not included and has to be added separately.
| Term | Meaning |
|---|---|
| Bushel | A US dry volume unit of 1.2445 cubic feet, the standard grain trading measure. |
| 0.8036 | Bushels per cubic foot, the reciprocal of 1.2445. |
| Grain height | The depth of grain, not the height of the bin. A part-filled bin uses the grain depth. |
| Peak | The cone of grain above the eave when a bin is filled beyond level, which adds capacity not counted here. |
The inputs explained
| Field | What to enter |
|---|---|
| Bin radius (ft) | Bin radius in feet, which is half the diameter. Bins are usually described by diameter, so halve it before entering. |
| Fill height (ft) | Depth of grain in feet, which is the fill height rather than the bin height unless the bin is level full. |
When to use it
Estimating what is in a bin
Measuring the grain depth and converting gives an inventory figure without weighing anything, which is the everyday use.
Planning storage for a harvest
Comparing expected yield against available bin capacity determines whether additional storage or immediate delivery is needed.
Sizing a new bin
Working backwards from the bushels to be stored gives the diameter and height combination required, and the squared radius means diameter is the more effective lever.
Worked examples
Every figure in the tables below is produced by this page’s own calculator at build time, so the numbers and the tool always agree. Select any row to load that scenario.
How much does each bin diameter hold?
A range of bin radii at a fixed 20 foot grain depth.
| Bin radius | Storage capacity | Bin volume | Bin diameter |
|---|---|---|---|
| 10 ft | 5,049 bu | 6,283 ft³ | 20.0 ft |
| 15 ft | 11,361 bu | 14,137 ft³ | 30.0 ft |
| 20 ft | 20,197 bu | 25,133 ft³ | 40.0 ft |
| 25 ft | 31,557 bu | 39,270 ft³ | 50.0 ft |
Questions
How many bushels in a cubic foot?
0.8036, since a US bushel is 1.2445 cubic feet. To go the other way, multiply bushels by 1.2445 to get cubic feet. The bushel is a volume measure, so the weight it represents differs by crop.
Does this include the peak of grain above the eave?
No, only the cylindrical portion to the grain depth you enter. A peaked bin holds a cone of grain on top, whose volume is one third of π times the radius squared times the peak height, and that has to be added separately.
What about a hopper-bottom bin?
The cone below the cylinder is not included either. Its volume is also one third of π times radius squared times cone height, calculated from the hopper dimensions and added to the cylindrical figure.
Does the grain type change the capacity?
Not the volume, but the weight. A bushel is a fixed volume, so the bin holds the same bushels of any grain, but a bushel of corn is about 56 lb and a bushel of soybeans about 60 lb. Test weight also varies within a crop, so bushels and pounds are not interchangeable.
For corn yield estimation before harvest, see the corn yield calculator. For field work rates, see the acres per hour calculator.