Grain Bin Calculator

About the Grain Bin Calculator

Knowing how many bushels your grain bin can hold is essential for harvest planning, grain marketing, and storage management. Grain bin capacity depends on the bin's shape and dimensions—diameter, eave height, and peak height for round bins, or length, width, and height for rectangular structures.

This calculator computes the capacity of round (cylindrical) grain bins with flat or peaked (cone-shaped) tops. For peaked grain, it calculates the additional bushels stored in the cone above the eave height. It supports all major grain commodities with their standard test weights, allowing you to convert between bushels, cubic feet, and metric tons.

Beyond simple capacity, the calculator estimates the total weight of stored grain (important for structural engineering and transportation planning), the grain surface area (relevant for aeration system design), and the fill percentage if your bin isn't completely full. Whether you're a farmer planning harvest logistics, a grain merchandiser estimating inventory, or an engineer sizing a new facility, this calculator provides the numbers you need.

When This Page Helps

Accurate bin capacity calculations prevent overselling (marketing more grain than you can store) and help you coordinate harvest equipment capacity with available storage. The weight calculations are critical for truck loading, rail car planning, and structural safety assessments.

How to Use the Inputs

1. Select your bin shape: round (most common) or rectangular.
2. Enter the bin diameter (or length/width for rectangular) in feet.
3. Enter the eave height (sidewall height) in feet.
4. If grain is peaked, enter the peak height above the eave in feet.
5. Select the grain type to apply the correct test weight (lb/bu).
6. The calculator displays total capacity in bushels, tons, and more.
7. Optionally enter actual fill height to see current inventory and fill percentage.

Example Calculation

Tips & Best Practices

• Always verify bin diameter by measuring circumference (C = π × D) and dividing by π.
• For marketing purposes, use conservative capacity estimates (flat fill, no packing factor).
• A 1-ft depth of grain in a 36-ft bin holds about 817 bushels of corn.
• Monitor grain condition throughout storage—capacity means nothing if grain quality deteriorates.
• Consider aeration fan sizing: 0.1-0.25 CFM per bushel for cooling, 1+ CFM/bu for drying.
• Keep records of actual fill amounts to calibrate your capacity estimates over time.

Grain Bin Geometry

Most commercial grain bins are cylindrical with corrugated steel walls. The straight wall (eave height) provides the primary storage volume. When grain is loaded through a center fill point, it naturally forms a cone shape on top with an angle of repose of about 23-28 degrees depending on the grain type and moisture content. Corn has an angle of repose around 25 degrees; soybeans about 24 degrees. This cone adds significant storage capacity—for a 36-ft bin, the peak can add 1,500-2,000+ bushels.

Test Weights and Grain Quality

Standard test weights used for bushel conversion are: corn 56 lb/bu, soybeans 60 lb/bu, wheat 60 lb/bu, oats 32 lb/bu, barley 48 lb/bu. However, actual test weight varies with grain quality, moisture content, and variety. High-quality corn might test at 58-60 lb/bu, while drought-stressed corn might only test 50-52 lb/bu. Lower test weight means lighter bushels and less total weight in the bin, affecting both marketing (price dockage) and structural loading.

Storage Planning and Management

Effective grain storage requires matching bin capacity to expected production, drying capacity, and marketing plan. A common rule of thumb is to have 100-125% of expected harvest in available storage, allowing for carryover grain and staging flexibility. Bins should be equipped with adequate aeration (fans, ducts, and temperature monitoring) to maintain grain quality. Temperature cables allow monitoring for hot spots that indicate spoilage. Proper storage is as important as growing the crop—a 1% loss in a 20,000-bushel bin costs the same as losing an acre of production.

Frequently Asked Questions

• How do I measure peak height?

  Peak height is the distance from the eave (top of the sidewall) to the highest point of the grain cone. For a full bin with a peaked roof, measure from the eave ring to the center of the grain surface.

• What is a bushel in cubic feet?

  One US bushel equals 1.2445 cubic feet. This is a volume measure. A "bushel" of grain also implies a standard test weight (e.g., 56 lb for corn, 60 lb for wheat).

• Why does grain type matter for capacity?

  Different grains have different test weights (density). While the volume in bushels is the same regardless of grain type, the weight per bushel varies. This affects structural loads and transportation limits.

• How much does a full bin weigh?

  Combined grain weight can be enormous. A 36-ft × 24-ft bin of corn holds about 25,000+ bushels weighing over 700 tons. Foundation and structural design must account for this load.

• Should I account for the hopper bottom?

  Yes, hopper-bottom bins have less capacity than flat-bottom bins of the same dimensions. The hopper cone subtracts volume. This calculator computes both configurations.

• What about grain packing and settling?

  Grain packed by mechanical spreading holds about 5-7% more than center-filled grain. Settled grain (after weeks of storage) may pack an additional 2-3%. Standard calculations assume center-fill without extra packing.