Grain Bin Volume and Capacity Calculator

Grain Bin Capacity Grain bins (also called silos or grain tanks) are cylindrical storage structures used to hold harvested grain. Capacity is measured in bushels, the standard unit for grain trading. Knowing exact capacity helps farmers plan storage, manage inventory, and calculate crop value.

The Formula Volume (cubic feet) = pi x (Diameter/2)^2 x Height. Bushels = Volume in cubic feet x 0.8036 (since 1 bushel = 1.2446 cubic feet). Folding pi/4 into that gives the single-line version for a round bin: Bushels = 0.6312 x Diameter^2 x Height, with both in feet.

You will see 0.628 quoted in a lot of bin charts. That comes from rounding 0.8036 down to a flat 0.8 bushels per cubic foot, and it runs about half a percent light. On a 36-foot bin that is around a hundred bushels, which matters when you are deciding whether this year’s crop fits.

Cone Top and Peaked Grain When grain is loaded from a center fill it forms a cone on top, and that cone is real storage: Cone bushels = 0.2104 x Diameter^2 x Height_of_cone, where the cone height is the bin radius times the tangent of the angle of repose.

The angle of repose is how steep a pile the grain will hold, and it varies more than people expect. Wheat sits at roughly 25 degrees, corn and soybeans around 27, barley and oats near 28, and rough rice as steep as 36. On a 36-foot bin that spread is the difference between a 2,300-bushel cone and a 3,500-bushel one, so the calculator uses each grain’s own angle rather than a single average.

Level fill or peaked? The calculator asks, because it changes the answer by more than 10%. Pick level if the grain has been leveled off, or if the height you measured is the grain surface rather than the eave. Pick peaked for a center-filled bin you have not touched.

How much the cone adds depends on the shape of the bin, and it varies more than the usual rule of thumb suggests. The cone height is set by the radius, while the cylinder below it grows with the eave height, so a squat wide bin gains far more from its peak than a tall narrow one. An 18 ft bin with an 18 ft eave picks up about 8% from a corn cone; a 48 ft bin with a 24 ft eave picks up about 17%. The calculator works out the figure for your bin rather than quoting a single number.

Grain Weights per Bushel Corn (shelled): 56 lbs/bushel. Soybeans: 60 lbs/bushel. Wheat: 60 lbs/bushel. Oats: 32 lbs/bushel. Barley: 48 lbs/bushel. Rice (rough): 45 lbs/bushel. Sunflower seeds: 30 lbs/bushel. These are the official “test weights” and the actual weight varies with moisture content.

Moisture Content Impact Grain must be dried to a safe moisture level before storage to prevent spoilage. Corn: store at 14% moisture or below. Soybeans: 13%. Wheat: 13.5%. Wet grain takes up more space per bushel of “dry equivalent”, so a bin full of 20% moisture corn holds fewer marketable bushels than the same bin full of 14% corn. The crop yield estimator works out that shrink from a harvest moisture reading.

Common Bin Sizes Farm bins run from 18 feet in diameter, which holds about 3,700 bushels level at an 18 ft eave, up to 48 feet, which holds roughly 34,900 bushels level at a 24 ft eave. Add the cone on top of that if the bin is center-filled, which is 8% on the small one and 17% on the large one. Commercial elevators use bins up to 105 feet across holding 300,000 bushels and more. A 1,000-acre corn farm yielding 200 bushels/acre brings in 200,000 bushels, so on-farm storage almost never covers the whole crop and the rest goes straight to the elevator at harvest-time prices.