Hong Life CalculatorsUnderstanding the grain bin capacity calculator — concept and principle
This calculator estimates how many bushels a round grain bin holds, including the cone of grain heaped above the wall line, and converts that to cubic feet, cubic metres and the weight in short tons and tonnes. Farmers use it to plan storage, check inventory and estimate the value of stored grain.
How it is calculated
- Floor area = π × (diameter ÷ 2)².
- Level part = floor area × grain depth at the wall.
- Peaked cone = floor area × peak height ÷ 3.
- Total volume (ft³) = level part + cone; m³ = ft³ × 0.0283168.
- Bushels = ft³ ÷ 1.2445, because one US (Winchester) bushel is 2,150.42 in³.
- Weight = bushels × test weight (lb per bushel); short tons = lb ÷ 2,000; tonnes = lb × 0.45359237 ÷ 1,000.
The principle
A full round bin is a cylinder of grain topped by a cone where the grain piles up under the fill spout. The cylinder is base area times height; a cone of the same base holds one third of the cylinder of the same height. The US bushel is a volume unit, so bushels come straight from cubic feet. Weight depends on the grain's test weight, the weight of one bushel: shelled corn is standardised at 56 lb and wheat and soybeans at 60 lb, but real test weights vary with moisture and quality.
Worked example
Default inputs: diameter 30 ft, grain depth at the wall 20 ft, peak 6 ft, test weight 56 lb/bu.
- Floor area = π × 15² = 706.9 ft².
- Level part = 706.9 × 20 = 14,137 ft³ = 11,360 bushels.
- Cone = 706.9 × 6 ÷ 3 = 1,414 ft³ = 1,136 bushels.
- Total = 15,551 ft³ (440.4 m³) = 15,551 ÷ 1.2445 = 12,496 bushels.
- Weight = 12,496 × 56 = 699,800 lb = 349.9 short tons = 317.4 tonnes.
| Bin diameter (ft) | Capacity (bushels) |
|---|---|
| 7.5 | 781 |
| 15 | 3,124 |
| 22.5 | 7,029 |
| 30 | 12,496 |
| 37.5 | 19,525 |
| 45 | 28,116 |
| 60 | 49,985 |
How to read the result
This is a loose-fill estimate. Grain packs down under its own weight in tall bins, so the real quantity can be higher than the figure shown. If the bin has a hopper bottom, add its cone separately; if the grain surface is level, set the peak to 0. Measure grain depth at the wall carefully, because it drives most of the volume.
Common mistakes
- Using the bin's eave height instead of the actual grain depth.
- Forgetting the peak, or counting it as a full cylinder.
- Using 60 lb/bu for corn or 56 lb/bu for wheat.
- Entering the radius instead of the diameter.
Frequently asked questions
How many bushels are in a 30 ft bin filled 20 ft deep?
About 11,360 bushels level, or about 12,500 with a 6 ft peak.
How many cubic feet are in a bushel?
About 1.2445 ft³ (2,150.42 cubic inches).
What does test weight mean?
The weight of one bushel of grain, such as 56 lb for shelled corn and 60 lb for wheat and soybeans.
Sources: NIST Office of Weights and Measures, G. D. Lee, "Determining Reference Test Weight per Bushel Value of Grains" (2013, updated 2017) · University of Missouri Extension, W. J. Murphy, "Tables for Weights and Measurement: Crops"