1. Level cylindrical grain
The level part of a round bin is a cylinder. Use inside diameter and the grain depth at the wall, not outside bin dimensions or total roof height.
Grain Bin Capacity Calculator: Bushels, Volume and Weight
Estimate the capacity of a round grain bin from its inside diameter, grain depth, surface profile and optional hopper bottom.
How the Grain Bin Calculation Works
2. Peak or withdrawal cone
A centred grain peak adds a cone. A centred inverted cone subtracts the same shape. Cone volume is one-third of a cylinder with equal base and height.
3. Bushels and weight
Cubic feet convert to estimated bushels using the selected basis. Bushels then multiply by the editable pounds-per-bushel value to estimate weight.
Formulas and Assumptions
Radius = inside diameter ÷ 2
Cylinder volume = π × radius² × level grain depth
Peak or hopper volume = π × radius² × vertical cone height ÷ 3
Total volume = cylinder + peak − inverted cone + hopper
Farm-estimate bushels = total ft³ × 0.8
Exact dry-volume bushels = total ft³ × 1,728 ÷ 2,150.42
Estimated weight = usable bushels × entered lb/bu
The cone calculations assume the peak, withdrawal depression or hopper is centred, circular and reaches the full inside bin diameter. Irregular surfaces should be measured at several locations and treated as an approximation. The usable capacity factor is applied to every section after geometry is calculated.
Worked Example: 30-Foot Bin with a 4-Foot Peak
A 30 ft inside-diameter bin with 18 ft of grain at the wall contains about 12,723.5 ft³ in its level cylindrical section. A 4 ft centred peak adds about 942.5 ft³. Total geometric volume is therefore about 13,666 ft³.
Using the farm factor of 0.8 bu/ft³ gives about 10,933 bushels. At 56 lb/bu, the estimated corn weight is about 612,234 lb, 306.1 short tons or 277.7 metric tonnes. Manufacturer ratings and measured inventories may differ for the reasons below.
Calculation Basis and References
- Iowa State University Extension: Storage Capacity for Grains, Forages, and Liquids — round-bin geometry, 0.8 bu/ft³ for corn or soybeans, and the one-third cone-height method.
- University of Minnesota Extension: Selecting Fans and Determining Airflow for Grain Bins — a worked round-bin capacity example using 0.8 bu/ft³.
- USDA Agricultural Marketing Service: Practical Procedures for Grain Handlers — Winchester bushel volume and test-weight definition.
These references support the calculation basis; they do not certify a particular bin, floor, hopper, foundation or grain condition.
Grain Bin Capacity Calculator FAQs
How do I calculate the bushel capacity of a round grain bin?
Find cylindrical volume with π × radius² × level grain depth. Add one-third of the equivalent cylinder for a grain peak or hopper, or subtract it for an inverted withdrawal cone. Convert the resulting cubic feet with the selected bushel factor.
How many bushels fit in one cubic foot?
The conventional farm estimate is 0.8 bu/ft³. A U.S. dry bushel is exactly represented here as 2,150.42 in³, which converts to about 0.803564 bu/ft³. The difference is roughly 0.44%.
How is a grain peak included?
Measure vertically from grain level at the wall to the highest centre point. The calculator treats this as a centred cone and adds one-third × π × radius² × peak height.
Does grain test weight change bin volume?
No. Geometry determines volume. The entered lb/bu value only converts estimated bushels to estimated weight. Actual inventory from scale weights may not match a geometry-based estimate.
Why can the result differ from the manufacturer's capacity?
Rated capacity may use a particular eave height, roof-fill slope, hopper shape and grain-packing basis. Ladders, ducts, temperature cables, wall corrugations, compaction, uneven filling and measurement error also affect usable space.
Can I calculate a hopper-bottom bin?
Yes. Choose Conical hopper and enter its vertical depth. This assumes the hopper is a complete centred cone with its upper edge matching the inside bin diameter; consult drawings for truncated or offset hoppers.
Are my bin measurements stored?
No. All calculation logic runs client-side in your browser, and this calculator does not send or store the values you enter.
Planning and Safety Limits
This calculator estimates inventory from simple geometry; it does not rate a bin, foundation, floor, hopper, roof, unload system or aeration equipment. Do not use estimated grain weight as a structural load approval. Verify dimensions and rated capacity with the bin manufacturer or a qualified grain-storage professional. Grain bins are hazardous confined spaces: follow applicable lockout, entry, fall-protection and rescue procedures, and never enter flowing or bridged grain. Workplaces covered by the rule should follow OSHA 29 CFR 1910.272 grain-handling requirements; other operations should follow the rules and professional guidance that apply locally.