Grain Bin Calculator
Compute grain bin using validated scientific equations. See step-by-step derivations, unit analysis, and reference values.
Formula
Bushels = [Pi x r^2 x h + (1/3) x Pi x r^2 x roof_h] / 1.2445
Total bin volume is the sum of the cylindrical body (Pi x radius squared x eave height) and the conical roof (one-third x Pi x radius squared x roof height). Roof height is calculated as radius x tangent of the roof pitch angle. The total cubic feet is divided by 1.2445 (cubic feet per bushel) to get capacity in bushels. Weight is then calculated by multiplying bushels by the standard weight per bushel for the specific grain.
Worked Examples
Example 1: Standard Farm Grain Bin
Problem: Calculate capacity of a 24-foot diameter bin with 18-foot eave height, 30-degree roof pitch, storing corn.
Solution: Radius: 24/2 = 12 ft\nCylinder volume: Pi x 12^2 x 18 = 8,143 cu ft\nRoof height: 12 x tan(30 deg) = 6.93 ft\nRoof cone volume: 1/3 x Pi x 12^2 x 6.93 = 1,045 cu ft\nTotal volume: 8,143 + 1,045 = 9,188 cu ft\nBushels: 9,188 / 1.2445 = 7,384 bu\nWeight: 7,384 x 56 = 413,504 lbs = 206.8 tons
Result: Capacity: 7,384 bushels | Weight: 206.8 tons of corn
Example 2: Large Commercial Bin
Problem: A 36-foot diameter bin with 24-foot eave height and 25-degree roof pitch stores soybeans.
Solution: Radius: 36/2 = 18 ft\nCylinder: Pi x 18^2 x 24 = 24,429 cu ft\nRoof height: 18 x tan(25 deg) = 8.39 ft\nRoof cone: 1/3 x Pi x 18^2 x 8.39 = 2,847 cu ft\nTotal: 24,429 + 2,847 = 27,276 cu ft\nBushels: 27,276 / 1.2445 = 21,916 bu\nWeight: 21,916 x 60 = 1,314,960 lbs = 657.5 tons
Result: Capacity: 21,916 bushels | Weight: 657.5 tons of soybeans
Frequently Asked Questions
How do I calculate grain bin capacity in bushels?
Grain bin capacity is calculated by determining the total volume in cubic feet and dividing by 1.2445 (cubic feet per bushel). For a round bin, the cylinder volume is Pi x radius squared x eave height. Add the cone-shaped roof volume (1/3 x Pi x radius squared x roof height) if grain is peaked to the roof. The roof height depends on the roof pitch angle. For a bin with a 24-foot diameter and 18-foot eave height with a 30-degree roof pitch, the cylinder holds about 8,143 cubic feet and the roof cone adds about 1,567 cubic feet, for a total of approximately 7,808 bushels.
How much does a full grain bin weigh?
The weight depends on bin size and grain type. Corn weighs 56 lbs per bushel at standard 15.5% moisture, soybeans and wheat weigh 60 lbs per bushel, and oats weigh only 32 lbs per bushel. A modest 24x18 bin holding about 7,800 bushels of corn weighs approximately 218 tons (437,000 lbs). This massive weight means proper concrete foundation design is critical. The foundation must support not only the grain weight but also wind loads, snow loads, and dynamic forces during filling and unloading. Always consult with a structural engineer for foundation specifications.
What is the recommended aeration rate for grain bins?
Aeration rates are measured in cubic feet per minute (CFM) per bushel. For maintaining grain condition (cooling and moisture management), a minimum of 0.1 CFM per bushel is recommended. For natural air drying, 0.5-1.0 CFM per bushel is needed. For high-temperature drying, 1.0-2.0 CFM per bushel may be required. For a 7,800-bushel bin, maintaining condition requires 780-1,950 CFM. Properly sized aeration fans and perforated floors or ducts are essential for moving air uniformly through the grain mass to prevent hot spots and moisture migration.
How does grain bin diameter vs height affect storage efficiency?
Shorter, wider bins have a lower cost per bushel of capacity because they require less steel per bushel and have lower foundation loads per square foot. However, taller bins with the same capacity have a smaller footprint, which matters when land area is limited. Taller bins also develop more grain depth, which increases static pressure on aeration systems, requiring larger fans. The most cost-effective bins for flat storage typically have a height-to-diameter ratio of 0.5 to 1.0. Hopper-bottom bins for easy unloading are typically taller relative to diameter but cost more per bushel of capacity.
Is my data stored or sent to a server?
No. All calculations run entirely in your browser using JavaScript. No data you enter is ever transmitted to any server or stored anywhere. Your inputs remain completely private.
Is Grain Bin Calculator free to use?
Yes, completely free with no sign-up required. All calculators on NovaCalculator are free to use without registration, subscription, or payment.