Grain Bin Capacity Calculator (Bushels, Tons, Peak & Hopper)
Bushels a round or rectangular grain bin holds from its diameter (or length and width) and grain depth, with a peaked top from a measured height or the angle of repose, a hopper (cone) bottom, compaction, weight in tons for corn, soybeans, wheat and other crops, how full the bin is, and a depth-by-depth capacity table.
How it works
Round bin: volume = π × r² × depth (+ π × r² × peak ÷ 3 for the peak cone, + π × r² × hopper ÷ 3 for a cone bottom) · rectangular: L × W × depth (+ W × peak ÷ 6 × (3L − W) for a peaked pile) · full peak = r × tan(angle of repose) · bushels = ft³ × 0.8036 (m³ × 28.38) × (1 + compaction) · weight = bushels × test weight
A round bin is a cylinder, so the level grain is the circular floor area times the depth. Because one US bushel is 1.2445 cubic feet, multiplying cubic feet by 0.8036 converts volume straight to bushels (a cubic metre is about 28.4 bushels). Grain piled above the eave forms a cone holding one-third of a cylinder the same height; enter its measured height, or let the calculator build a full peak from the angle of repose, the slope a grain pile takes as it fills. A hopper-bottom bin adds another cone underneath. Rectangular and flat storage piles slope on all four sides like a hip roof. Under More options you can add a compaction factor (deep bins pack grain a few percent tighter than its loose volume), the measured test weight, the wall height to see how full the bin is, several identical bins and a price per bushel. The weight uses the crop’s standard bushel weight unless you enter a test weight, and the table shows capacity at every depth for reading off a measured grain line.
Worked example
A 24 ft diameter bin has a radius of 12 ft and a floor area of π × 12² ≈ 452.4 ft². Filled level to 20 ft deep that is 9,048 ft³, and 9,048 × 0.8036 ≈ 7,271 bushels — about 203.6 short tons of corn at 56 lb/bu. Peaking it at a 25° fill angle adds a 5.6 ft cone (12 × tan 25°) of 452.4 × 5.6 ÷ 3 ≈ 844 ft³, or 678 bushels, for 7,949 in total. Each foot of depth in this bin is worth about 364 bushels.
Sources: Iowa State University Ag Decision Maker — Storage formulas (C6-82) · NIST Handbook 44 — US bushel = 2,150.42 in³ · USDA — bushel volume standard
Frequently asked questions
Why 0.8036 bushels per cubic foot?
One US bushel is defined as 2,150.42 cubic inches, or 1.2445 cubic feet, and 1 ÷ 1.2445 ≈ 0.8036. Extension shortcuts round it to 0.8, which reads about half a percent low. Some online calculators use smaller constants that build in settling or loose fill; this one keeps the exact volume and lets you add compaction separately.
Does the grain type change capacity?
In volume bushels, no — a cubic foot is a cubic foot. What changes is the weight per bushel (corn and sorghum 56 lb, wheat and soybeans 60, barley 48, oats 32) and how much the grain packs. Pick the crop to get tons, and enter a measured test weight under More options to see the paid (weight) bushels.
How do I measure the peak or use the angle of repose?
If you can measure it, enter the height of the grain cone above the level line at the wall. If the bin is filled to a full peak and you cannot climb it, choose “Full peak from angle”: the peak is the radius times the tangent of the fill angle, roughly 20–28° for most grains (25° is a common planning figure). Leave the peak at zero for a level or partly filled bin.
How much does grain compaction add?
Grain settles under the weight above it, so tall bins hold more than their geometric volume — commonly 3–8% for corn, wheat and soybeans, and more with deeper bins and higher moisture. Manufacturer capacity charts usually quote the uncompacted figure. Enter a percentage under More options to include it.
How do I figure a hopper-bottom bin?
Add the cone underneath: its volume is one-third of the floor area times the hopper height. Enter the hopper height under More options and the calculator adds those bushels to the bin above it.
How many bushels per foot does a bin hold?
Floor area × 0.8036. An 18 ft bin holds about 204 bushels per foot of depth, a 24 ft bin 364, a 30 ft bin 568, a 36 ft bin 818 and a 48 ft bin 1,454. The table on this page lists common diameters.
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This calculator is for educational purposes. Double-check important results before acting on them.