Grain Bin Capacity Calculator

A bushel is a unit of dry volume, not weight — 1 US Winchester bushel equals exactly 2,150.42 cubic inches, or about 1.24446 cubic feet, and comes from a 17th-century English standard for grain measure. It has survived in the US and Canadian grain trade because the whole supply chain — farmers, elevators, futures markets on the CBOT, USDA reports — quotes crops in bushels. The pound-per-bushel test weight lets you convert between bushels (a volume) and pounds (a mass) at a standard density for each grain, which is how grain moves between the two units on invoices and shipping tickets.

The extension tables use rounded coefficients — 0.6283 for the cylinder factor and 0.2094 for the cone factor — that combine π and 1.24446 into a single number. Rounding those two constants to four significant figures drops about 0.5% of the true capacity. This calculator carries π to full double-precision and 1.24446 to five decimal places, so the raw geometric answer is 0.4–0.6% higher than the table value on the same diameter and height. For farm-scale planning that difference is smaller than the pack settling of the grain itself, so either number is fine; the calculator matches the pure math, the table matches the historical printout.

Inside diameter, always. The storage volume is bounded by the inner face of the corrugated wall, not the outside skin. On a typical farm bin the corrugation and stiffener add only about half an inch to the outside diameter per side, so the difference is under 1 bushel per foot of height on a 30-ft bin — but on a large commercial bin the numbers get real. The manufacturer spec sheet always quotes inside diameter (Sukup, Brock, GSI, Sioux Steel all agree on this); if you are measuring a bin on-farm, drop a tape from the top ring inside the wall.

For a partly-filled cylinder, replace the wall height H with the depth of grain measured from the floor to the top of the pile. If the grain is heaped rather than level (which it will be if it was augered in from the centre), you still have the cone geometry — measure the vertical distance from the level surface up to the peak and enter it as the peaked-roof height. A quick rule of thumb: corn augered dead-centre piles to an angle of repose of about 23°, so on a 30-ft diameter bin the peak sits about 6.4 ft above the level of the outer edge. Use that as the peak height if you cannot climb up and measure.

The calculator uses the USDA Federal Grain Inspection Service standard test weights that apply to No. 1 or No. 2 grade grain — 56 lb/bu for corn and sorghum, 60 for wheat and soybeans, 48 for barley, 32 for oats. Off-standard grain trades at its own tested weight: light corn from a drought year might come in at 52 lb/bu, plump hard red winter wheat can hit 63. If you know the actual test weight from an elevator ticket, take the bushel figure from the calculator and multiply by that number instead of the standard. The bushel count itself is a pure geometry number and does not change with grain quality.

This calculator models a flat-bottom bin — the concrete-floor design that most farm storage uses. For a hopper-bottom bin (steel cone underneath, feeding onto trucks by gravity), add the hopper cone volume separately using the same one-third-of-a-cylinder formula: (1/3) × π × (D/2)² × hopper_depth. Most commercial hoppers have a 45° or 60° discharge angle, so a 24-ft diameter hopper adds about 12 ft of vertical drop and roughly 1,800 bushels of hopper storage — worth counting when you are sizing a bin farm.