Grain Bin Capacity Calculator - Bushels & Cubic Feet

What is a grain bin capacity calculator?

A grain bin capacity calculator finds how much grain a round, straight-sided storage bin can hold. It takes two measurements, the bin's diameter and its height, and returns the volume in cubic feet and the matching capacity in bushels. Farmers and grain elevator operators use it to plan harvest logistics, size equipment, and decide how much grain fits on site.

This calculator accepts a diameter and a height from 1 to 100 feet, in steps of 0.1 feet.

How to calculate grain bin capacity

The volume formula

A straight-sided bin is a cylinder, so its volume follows the standard cylinder formula:

$V = \pi \times r^2 \times h$

Here $V$ is the volume in cubic feet, $r$ is the radius of the bin in feet, and $h$ is the height in feet. The radius is half the diameter, so $r = d \div 2$. Written with the diameter, the same formula is $V = \pi \times (d/2)^2 \times h$, which is what the calculator uses.

Use the inside diameter of the bin, not the outside diameter. Steel bin walls and their corrugation add a few inches. On a 30-foot bin, measuring across the outside ridges overstates the volume by several hundred bushels.

Converting cubic feet to bushels

Once the volume is known, one fixed factor turns cubic feet into bushels:

$\text{Bushels} = \text{Cubic feet} \times \frac{1728}{2150.42} \approx \text{Cubic feet} \times 0.8036$

That factor comes from the definition of the unit. One US bushel is exactly 2,150.42 cubic inches, a measure called the Winchester bushel. One cubic foot is 1,728 cubic inches. Dividing gives 1,728 ÷ 2,150.42 ≈ 0.8035639549 bushels per cubic foot. The calculator uses the full value, not the rounded 0.8 that grain traders often quote in their heads. On the 30 by 24 foot bin below, the rounding difference is about 60 bushels.

Worked example

Consider a bin 30 feet in inside diameter and 24 feet tall.

1. Radius: $r = 30 \div 2 = 15$ feet.
2. Volume: $V = \pi \times 15^2 \times 24 \approx 16{,}964.60$ cubic feet.
3. Capacity: $16{,}964.60 \times 0.8035639549 \approx 13{,}632.14$ bushels.

The calculator's starting example, a 15-foot by 20-foot bin, works the same way: $\pi \times 7.5^2 \times 20 \approx 3{,}534.29$ cubic feet, which is about 2,840.03 bushels.

Both figures are rated capacity: the theoretical maximum for a bin filled to the eave with level grain.

Rated capacity versus usable capacity

Real bins usually hold a little less than the formula says. Several things account for the gap.

• Equipment inside the bin. Aeration tubes, sumps, and sweep augers take up space grain cannot fill. A 12-inch aeration tube running the full 25-foot height of a bin has a radius of 0.5 feet, so it occupies $\pi \times 0.5^2 \times 25 \approx 19.63$ cubic feet, or about 15.78 bushels. In a 16,965 cubic foot bin that is roughly a tenth of one percent. Larger sumps and transition cones take more.
• Grain piling. Grain peaks in the middle as a bin fills. A bin without a spreader rarely fills level, so the corners near the wall stay empty.
• Headspace. Operators leave room at the top for airflow and to avoid spilling during loading.
• Packing and moisture. Grain settles under its own weight, and damp grain packs differently from dry grain. Both shift the real bushel count away from the plain volume figure.

Because of these effects, planning figures are usually a few percent below rated capacity. Manufacturer capacity charts for a specific bin model are the most reliable source.

Cone tops and hopper bottoms

If grain is allowed to peak above the sidewall, the peak is a cone. Its volume uses the cone formula:

$V_{cone} = \frac{1}{3} \times \pi \times r^2 \times h_{cone}$

For a 30-foot bin with a 5-foot peak, that is $\frac{1}{3} \times \pi \times 15^2 \times 5 \approx 1{,}178.10$ cubic feet, or about 946.68 bushels, on top of the cylinder. A hopper-bottom bin has a cone under the cylinder instead, and its volume is found with the same formula. This calculator covers the straight-sided section only, so cone volume has to be added separately.

Volume bushels and weight bushels

Grain is bought and sold by the weight bushel, not the volume bushel. US grain standards fix a test weight for each crop, so "one bushel" of a crop means that many pounds.

The volume conversion above does not change from crop to crop, because a bushel is a fixed volume. What changes is the weight in the bin. To estimate weight, multiply the bushels from the calculator by the pounds-per-bushel figure for the crop. A 13,632-bushel bin of corn holds roughly 13,632 × 56 ≈ 763,400 pounds, or about 382 tons.

Frequently asked questions

How close is the calculated figure to what a bin really holds?

The geometry is exact, but usable capacity is normally a few percent lower. The gap comes from equipment inside the bin, uneven piling, and headspace, not from an error in the arithmetic.

Can this be used for grains other than corn?

Yes. The volume in cubic feet and the bushel count are the same for any crop, because a bushel is a unit of volume. Only the weight of that grain changes, which the table above covers.

How should bin diameter be measured?

Measure the inside diameter of an empty bin if possible. Otherwise measure the outside diameter and subtract twice the wall thickness. Measuring across the corrugation ridges outside the bin overstates the diameter and inflates the result.

Why 0.8036 bushels per cubic foot and not 0.8?

One bushel is defined as 2,150.42 cubic inches and one cubic foot is 1,728 cubic inches, so the ratio is 1,728 ÷ 2,150.42 ≈ 0.8036. The 0.8 shortcut is easier to do in the head but runs about 0.44 percent low, which matters on a large bin.

Does the calculator handle cone tops or hopper bottoms?

No. It measures the straight-sided cylinder only. A cone top adds volume and a hopper bottom adds a cone below the sidewall; both are calculated with the cone formula shown above and added to the result.

References

1. National Institute of Standards and Technology, Handbook 44: Specifications, Tolerances, and Other Technical Requirements for Weighing and Measuring Devices, Appendix C, for the US bushel of 2,150.42 cubic inches.
2. US Department of Agriculture, Federal Grain Inspection Service, United States Standards for Grain (7 CFR Part 810), for test weight per bushel.
3. Hellevang, K. J., Grain Drying, Handling and Storage Handbook, North Dakota State University Extension.