Grain Bin Size Calculator: Capacity and Dimensions

Calculate a grain bin’s approximate capacity by entering its diameter and the height of the cylindrical wall; the calculator returns the bin’s volume in cubic feet and bushels. It assumes a flat-bottom cylinder filled to the top of the wall, so it does not include a roof, cone, headspace, or losses from grain that does not pack uniformly.

Formula

For a cylindrical bin, volume is the area of its circular base multiplied by the height:

V = π × (D ÷ 2)² × H

To express that volume as a standard U.S. dry bushel equivalent, divide cubic feet by 1.244456 cubic feet per bushel, or multiply by about 0.803563:

B = V ÷ 1.244456

• D is the inside diameter, in feet.
• H is the straight cylindrical wall height, in feet.
• V is the cylindrical volume, in cubic feet (ft³).
• B is approximate volume capacity in U.S. bushels.

The bushel conversion is a volume conversion, not a weight estimate. Actual grain weight depends on the crop, moisture, test weight, and how the grain settles. The calculator uses feet so its inputs match the output formula; convert measurements given in inches by dividing by 12, or measurements in metres by multiplying by 3.28084.

Worked Example

Using the calculator’s defaults, the diameter is 30 ft and the straight wall height is 30 ft. The radius is 30 ÷ 2 = 15 ft.

1. Base area = π × 15² = 706.858 ft² (approximately).
2. Cylindrical volume = 706.858 × 30 = 21,205.8 ft³ (approximately).
3. Bushel capacity = 21,205.8 ÷ 1.244456 = 17,044.9 bushels (approximately).

Rounded to the calculator’s settings, the result is 17,045 bushels, with a cylindrical volume of 21,205.8 ft³. The bushel output is rounded to a whole bushel; it is still a geometric estimate, not a guaranteed usable storage quantity.

How to Measure a Grain Bin

Measure the bin’s inside diameter across the circular floor or interior wall, and measure the vertical height of the straight-sided section. If you only have outside dimensions, wall thickness means the inside diameter will be slightly smaller; use manufacturer drawings or a reliable measurement rather than assuming the two are identical.

Do not automatically use the bin’s overall height. A roof may rise above the wall, and some bins have a sloped hopper or cone beneath the cylindrical section. Those parts have different shapes and need separate volume calculations. For a flat-bottom bin, grain piled into a peaked surface can also add volume beyond the cylinder, while leaving headspace reduces the amount actually stored.

What the Capacity Means

A bushel is a unit of volume. In U.S. dry measure, one bushel is 2,150.42 cubic inches, or approximately 1.244456 ft³. Thus, this calculator converts the geometric volume into bushels using a fixed conversion factor; it does not convert bushels into pounds or tonnes.

For a rough weight estimate, a separate crop-specific test-weight figure is needed. Multiply bushels by the applicable pounds-per-bushel value to estimate pounds, then divide by 2,204.62 to convert pounds to metric tonnes. Such a result remains approximate because grain condition and measurement practices affect actual bulk density. Do not treat nominal bushel capacity as a safe structural load limit.

When This Estimate Is Useful—and Its Limits

The cylinder formula is useful for comparing possible bin sizes, checking a basic capacity claim, or estimating the volume of a simple upright bin. It is most appropriate when the interior is cylindrical, the dimensions are known, and the desired answer is a theoretical brim-full volume of the straight-wall section.

• Roof space: A peaked roof can hold additional grain, but its volume depends on roof shape and fill level. It is excluded here.
• Headspace: Grain may be kept below the roof or eaves. Subtract the unfilled cylindrical height using the same formula if you know it.
• Hoppers and sloped floors: A cone or truncated cone is not a cylinder. Calculate its volume separately and add it only if it is part of the usable storage space.
• Practical capacity: Grain flow, aeration equipment, access openings, and operating limits can make usable capacity differ from geometric capacity.

For a more accurate operating figure, consult the bin’s dimensional chart or technical documentation and follow appropriate loading and operating instructions. The calculator cannot determine whether a particular bin, foundation, or floor can safely support a given load.

Common Calculation Mistakes

• Using radius as diameter: The formula squares the radius, which is half the diameter. Entering a radius in the diameter field makes the calculated volume one quarter of the intended value.
• Mixing units: Do not enter inches as though they were feet. Convert all lengths to feet first, or convert all measurements consistently and use a matching formula.
• Including the roof height: The default calculation includes only straight wall height. Adding roof height to the wall height falsely treats the roof as another cylinder.
• Confusing volume with weight: A bushel here represents a standard volume. The mass held in that volume varies with grain type and condition.
• Overinterpreting rounding: The displayed whole-bushel figure does not imply that a bin can be loaded to that exact amount in real use.

Frequently Asked Questions

How many bushels fit in a grain bin?
For a straight-sided cylindrical bin, calculate π × (diameter ÷ 2)² × wall height in cubic feet, then divide by 1.244456. The result is an approximate volume in U.S. bushels.

Do I measure the grain bin diameter or radius?
Measure the diameter across the full circle. The formula halves that measurement to obtain the radius, so do not enter the radius in a diameter field.

Does grain-bin capacity include the roof?
No. This calculator models only the cylindrical wall section. Roof storage must be estimated separately using the roof’s shape and the actual grain fill level.

How do I calculate grain bin capacity in metric units?
Convert metres to feet by multiplying by 3.28084, use the calculator, then convert cubic feet to cubic metres by multiplying by 0.0283168. A U.S. bushel is a volume unit, so bushel output can also be converted to litres using 1 bushel ≈ 35.239 litres.

Can I calculate how many tonnes of grain a bin holds?
Not from dimensions alone. First estimate bushels, then use a suitable crop-specific weight per bushel. The resulting tonnes are approximate and do not establish a safe load limit.

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in d | Bin diameter | ft | 30 | 0
in h | Straight wall height | ft | 30 | 0
out b | Approximate capacity | bushels | pi * d^2 / 4 * h * 0.803563 | 0
out v | Cylindrical volume | ft^3 | pi * d^2 / 4 * h | 1