Grain Bin Calculator

How to use this grain bin calculator

What this calculator does. This tool estimates the geometric volume of grain inside a round or rectangular storage bin, converts that volume to U.S. bushels, and multiplies the bushel estimate by a grain test weight to obtain a total stored weight. It is useful for planning storage, checking whether a harvest lot is likely to fit, comparing bins, and creating a reproducible capacity worksheet. It is not a structural engineering check, a settlement survey, or an official inventory measurement. Real grain surfaces are irregular, compact differently, and may include void space, so the result should be treated as a planning estimate.

When to use it. Use the calculator before harvest to compare expected production with available storage, while filling a bin to estimate current inventory from measured grain depth, when evaluating a new round or rectangular bin, or when converting a physical bin measurement into bushels and weight for logistics. The University of Minnesota Extension uses the same basic cylindrical capacity relationship in its guidance on selecting fans and determining airflow for grain bins.

How to calculate.

1. Select Grain bin type. Choose Round for a cylindrical bin or Rectangular for a box-shaped flat store.
2. Select the Dimension unit. Feet is the default; switching to Metres converts every current dimension and updates the unit labels.
3. For a round bin, enter Diameter; the read-only Radius is calculated automatically. For a rectangular bin, enter Length and Width.
4. Enter Sidewall height, meaning the straight-sided grain depth. Select a Roof / peaked grain option and enter Roof peak height only when the grain surface forms a cone. Select Hopper bottom and enter Hopper height when a tapered bottom contains grain.
5. Enter Grain test weight in pounds per bushel. Read the live bushel, volume, and weight results, review the capacity breakdown, then use Download Excel to export the current state. Use Reset to restore the documented defaults.

Input guide. Diameter, Length, Width, Sidewall height, Roof peak height, and Hopper height accept positive decimal values in the active unit; examples are 30 ft diameter, 40 ft length, 20 ft sidewall height, a 6 ft peak, and an 8 ft hopper. Commas are accepted only as thousands separators in an en-US number such as 1,200.5; decimal-comma text such as 1,5 is rejected rather than silently changed. Zero is allowed only for optional roof and hopper heights when their sections are not selected. Grain test weight is required, must be greater than zero, and commonly ranges by crop and grade; 56 lb/bu is a practical corn example. USDA explains that test weight is the weight of grain filling a Winchester bushel in its Grain Grading Primer. Increasing any active dimension raises capacity; increasing test weight leaves volume unchanged but raises total weight.

Output guide. Grain volume in bushels is the main capacity estimate. Volume of grain shows cubic feet and Metric volume shows cubic metres. Total grain weight is pounds, while Weight in metric tonnes provides a metric logistics figure. The summary pills report the active shape, unit system, roof state, and hopper state. The Capacity breakdown table separates Body, Roof peak, Hopper, and Total so you can see exactly which geometry contributes to the result. A zero roof or hopper row means that optional section is not active, not that the whole bin is empty.

Worked example. With a round bin 30 ft in diameter and 20 ft high, no roof peak, no hopper, and a test weight of 56 lb/bu, the radius is 15 ft. The body volume is π × 15² × 20 = 14,137.17 ft³. Using 0.7786 bushel per cubic foot gives 11,007.20 bu. Multiplying by 56 lb/bu gives 616,403.10 lb, or about 279.60 metric tonnes. These values match the default calculator state and the exported workbook.

Learn more. The volume conversion used here follows the agricultural approximation of 0.7786 bu/ft³. For legal unit context, NIST lists the U.S. struck bushel as 2,150.42 cubic inches in Handbook 44, Appendix C. Because physical grain condition matters, review University of Minnesota Extension guidance on managing stored grain to minimize losses before treating a geometric estimate as an operational plan.