Grain bin calculator: bushels and tonnes from diameter and height
This grain bin calculator estimates how much grain a round bin holds. Enter the diameter and the depth of grain in the straight wall, choose a flat floor or a cone or hopper bottom, and say whether the grain is levelled or heaped into a peak. You get bushels, pounds, short tons and tonnes for corn, wheat, soybeans and other crops.
The maths is plain geometry, shown in full below, so you can check it against a bin maker’s capacity chart. It is useful before harvest, when deciding what to sell, or when working out how much bin space a field’s yield will need.
How to use the Grain Bin Calculator
- Choose feet and bushels, or metres and tonnes, and pick the grain. The test weight fills in, and you can edit it.
- Enter the bin diameter and the grain depth in the straight wall (the eave height for a full bin).
- Choose flat or cone / hopper floor. For a hopper, enter its height and the outlet diameter; use 0 for a pointed cone.
- Choose a peaked top and the angle of repose, or a level top. Add a packing allowance if you want one.
- Read the bushels and weight, and the split between wall, hopper and peak.
Grain Bin Calculator features
Three parts of the bin
The straight wall is a cylinder, a hopper bottom is a cone or frustum, and a heaped top is a cone sitting on the grain.
Bushels, pounds and tonnes
One US bushel is 2,150.42 in³ (1.2445 ft³), the figure in NIST Handbook 44. Weight comes from the test weight you set.
Crop test weights
Standard bushel weights fill in for corn (56 lb), wheat and soybeans (60), barley (48), oats (32), sorghum (56), rough rice (45) and canola (50).
Bushels per foot
See how many bushels each extra foot of grain adds, which is handy when you are part-filling a bin.
Feet or metres
Switching the unit converts the lengths you typed.
The grain bin formulas
For other solids and unit conversions, the volume calculator and weight converter cover the rest.
| Part | Volume | Notes |
|---|---|---|
| Straight wall | π × r² × h | r is half the diameter; h is grain depth in the wall |
| Cone / hopper bottom | π × H ÷ 3 × (R² + R·r + r²) | R is the bin radius, r the outlet radius (0 for a cone) |
| Peak on top | π × R² × (R × tan θ) ÷ 3 | θ is the angle of repose |
| Bushels | volume in ft³ ÷ 1.244456 | 1 bu = 2,150.42 in³ |
| Weight | bushels × test weight | Divide pounds by 2,000 for short tons |
Worked example: a 27 ft bin of corn
A bin 27 ft across filled to 24 ft has a radius of 13.5 ft, so the wall holds π × 13.5² × 24 = 13,741 ft³. A 25° peak rises 13.5 × tan 25° = 6.3 ft and adds π × 13.5² × 6.3 ÷ 3 = 1,201 ft³. The total is 14,942 ft³, or 12,007 bushels. At 56 lb per bushel that is 672,000 lb, 336 short tons or 305 tonnes of corn.
What changes the real number
- Test weight. It moves with moisture, variety and damage. Wet or light grain weighs less per bushel, so a bin holds fewer pounds.
- Packing. Grain compacts under its own weight, especially in tall bins, so the real bushel count is often a little higher than the simple volume. Enter your own allowance if you know it.
- Angle of repose. It depends on the grain, moisture and fines. The tool lets you set it; the bin maker’s data is better than a default.
- Bin details. Aeration floors, sump areas, wall ribs and the roof limit the peak, so check the manufacturer’s chart.
Grain Bin Calculator FAQ
How do I calculate bushels in a grain bin?
Find the volume in cubic feet (π × radius² × grain depth, plus any hopper and peak) and divide by 1.2445. A 27 ft bin with 24 ft of grain holds about 11,040 bushels in the wall alone.
How many bushels per foot are in my bin?
Bushels per foot = π × radius² ÷ 1.2445. For a 27 ft bin that is about 460 bushels for each foot of depth.
How do I calculate a bin with a cone bottom?
Add the cone or frustum volume under the wall: π × height ÷ 3 × (R² + R·r + r²). Set the hopper height and the outlet diameter in the calculator; use 0 outlet for a pointed cone.
How many pounds is a bushel of corn, wheat and soybeans?
The usual trade figures are 56 lb for shelled corn and 60 lb for wheat and soybeans. Your buyer’s scale ticket, moisture and local rules decide the actual figure.
What is the angle of repose of grain?
It is the steepest angle at which a heap stands without sliding, roughly 20–30° for most grains. Use your bin’s engineering data when you have it.
Is this calculator exact?
No. It is a geometric estimate. For contracts, use scale weights, and for safety follow grain bin rules: never enter a bin of stored grain without a plan and a spotter.