Grain Bin Capacity Calculator: Volume, Dry Bushels and Measured Mass

Use this when you need to know how much grain a round, flat-floor bin holds at its current fill. Enter the inside diameter, the grain depth at the sidewall and whether the surface is level, peaked or dipped to get grain volume and US dry bushels (a volume measure). Enter measured bulk density to estimate mass, then choose a grain type to convert that mass into market-weight bushels. Hopper-bottom bins are not modeled.

Three Quantities: Volume, Inventory Mass and Market Bushels

A US dry bushel is a volume of 0.03523907016688 m³. “Dry” names the measuring unit; it does not mean the grain has been dried to a target moisture. The volume answer describes the space occupied by grain, regardless of crop or density.

Inventory mass is estimated from that volume and your measured bulk density. It is not a scale measurement of the entire bin. A test-weight sample can inform the estimate, but moisture, fines and settling can make the average density in the bin different from a small sample.

Market-equivalent bushels divide estimated inventory pounds by the selected crop’s standard pounds per bushel. For shelled corn the divisor is 56 lb. Selecting corn sets that divisor only; it never fills the density field. These bushels do not include buyer moisture adjustments, grade discounts or drying charges.

From Harvest Planning to Stored Inventory

Compare expected harvest with available bin space using the yield estimator, keeping its crop yield units separate from this tool’s volume units. The harvest loss calculator helps estimate grain left in the field before you reconcile stored inventory.

If stored grain will become feed, carry forward the density-based mass and check the ration’s moisture basis with the feed ration builder. For forage storage alongside grain, use the hay bale needs calculator to plan a separate winter forage supply.

Inputs Explained

Inside diameter (D): Wall-to-wall distance inside the bin, above 0 and up to 100 m (328.08 ft). Measure inside the corrugations, not the outside of the roof eave.
Grain depth at the sidewall (H): Height of the grain where it meets the wall, measured from the flat floor, 0 to 60 m (196.85 ft).
Grain surface shape: Level for a flat top, peaked for a cone of grain rising to the centre, or inverted for a cone-shaped dip after unloading from the centre.
Surface rise or drop (h): How far the centre sits above (peak) or below (inverted) the grain at the wall, 0 to 30 m (98.43 ft). An inverted dip cannot be deeper than H. Not used for a level surface.
Measured bulk density (optional): Bulk or test density you measured for the grain in this bin, 1 to 2000 kg/m³ (0.08 to 155.38 lb per US dry bushel). Leave blank for volume only; no density is assumed.
Grain type (optional): Sets the standard market bushel weight (for example 56 lb for shelled corn) used to turn measured mass into market-weight bushels. It never sets the density.
Price (optional): Your own finite, non-negative price in the selected currency per metric tonne (1000 kg) or standard-weight market bushel. No market price is looked up. Density is required; market-bushel pricing also needs a grain type. Values too large to display safely are rejected; leave blank for no value estimate.

How This Calculator Works

Based on: Iowa State University Extension, Storage Capacity for Grains, Forages and Liquids (Ag Decision Maker C6-82): cylinder volume π × r² × H plus or minus a cone π × r² × h ÷ 3, with 1 US dry bushel = 1.2445 ft³ (0.03523907 m³)

Best for: Estimating the grain volume in a round, flat-floor bin and, with a measured density, its mass

Check locally: Measure the inside diameter and the grain depth at the wall, and use a bulk density from a sample of the grain in this bin

Units supported: Metric (m, m³, kg/m³, t), Imperial (ft, ft³, lb per US dry bushel, lb)

Formula

r = D ÷ 2; V_cylinder = π × r² × H: Inside diameter D and sidewall grain depth H are in metres; cylinder volume is in m³.
V_surface = s × π × r² × h ÷ 3; V_total = V_cylinder + V_surface: Surface rise/drop h is in metres. s is +1 for a peak, −1 for a central depression and 0 for level grain. The depression is a geometric subtraction using the same cone model.
US dry bushels by volume = V_total ÷ 0.03523907016688: Exact dry-volume unit conversion; no crop weight or moisture correction is applied.
Mass_kg = V_total × measured density_kg/m³; Mass_t = Mass_kg ÷ 1000: Only available when you enter measured bulk density. Imperial density in lb per US dry bushel is converted to kg/m³ before multiplication.
Market bushels = (Mass_kg ÷ 0.45359237) ÷ crop standard_lb/bu: Only available with density and a selected grain type. This converts mass to standard-weight market units.
Value = Mass_t × user price/t OR Market bushels × user price/market bu: Uses only your chosen price basis and currency, without an automatic price, exchange rate or buyer deductions.

Source

Storage Capacity for Grains, Forages and Liquids (C6-82) (opens in a new tab), Iowa State University Extension and Outreach — Round-bin geometry and average grain depth H + h/3 for a central peak; its approximate crop capacity factors are not used as measured bulk density here.
Handbook 44, Appendix C: General Tables of Units of Measurement (opens in a new tab), National Institute of Standards and Technology — US struck bushel: exactly 2150.42 cubic inches, converted here to 0.03523907016688 m³.
Weights, Measures, and Conversion Factors for Agricultural Commodities and Their Products (opens in a new tab), USDA Economic Research Service — Commodity weight conversions, including 56 lb per bushel of shelled corn; standard weights define market units, not measured bin density.

Assumptions

The bin is round with vertical walls and a flat floor. D is the inside diameter, H is measured from the floor to the grain at the wall, and h is measured relative to that wall level.
A peak or depression is a centred, symmetric cone spanning the full bin diameter. A level surface contributes no cone volume; a zero rise/drop is allowed.
Diameter must be positive and total volume must exceed zero. A depression cannot be deeper than H. The displayed dimension and density bounds are input limits, not structural design ratings.
A supplied measured density represents the whole inventory. No density default, packing correction or automatic moisture adjustment is applied in this form. Calculations retain full precision; results are rounded only for display.

Worked Example

A round, flat-floor bin 6 m across with grain 5 m deep at the wall and a central peak 1.2 m high

1. Cylinder
π × 3² × 5 = 141.37 m³
2. Peak cone
π × 3² × 1.2 ÷ 3 = 11.31 m³
3. Total volume
141.3717 + 11.3097 = 152.6814 m³ (152.68 m³ displayed)
4. Dry volume bushels
152.6814 ÷ 0.03523907016688 ≈ 4,332.73 US dry bu (calculated from unrounded volume)

The bin holds 152.68 m³, about 4,332.73 US dry bushels by volume. Mass stays hidden until a measured bulk density is entered.

How to Interpret Your Results

Condition	What It Means
Dry volume bushels	A measure of space, not weight. Two bins with the same volume can hold different masses of grain.
Estimated mass shown	Volume multiplied by the bulk density you entered. Its accuracy follows the density measurement.
Market-equivalent bushels	Estimated mass from measured density divided by the standard market bushel weight for the grain type. It is not the same number as the volume bushels.

Limitations and Cautions

Hopper bottoms, rectangular bins, sloping floors, off-centre peaks, crusts, uneven loading and internal obstructions are outside this model. Do not add a hopper depth to H; use a geometry method that includes the actual floor.
Diameter is squared in the volume formula, so diameter measurement error has a larger effect than the same relative depth error. An irregular surface needs several measurements rather than one assumed cone.
Illustrative example only: entering 750 kg/m³ for the 6 m / 5 m / 1.2 m peaked bin gives about 114.51 t. This density is not a recommended crop default or a measurement of your grain. Replace it with your own representative measurement.
User prices are planning inputs, not market quotes. The value is gross inventory value before moisture shrink, drying, storage, handling, transport and buyer deductions. Confirm quantity and price basis against scale tickets and the sale contract.
This tool does not certify structural capacity, safe fill height, grain quality or storage life. Obtain measurements without entering stored grain or climbing an unsafe structure; follow your site’s grain-bin safety procedures.

Common Mistakes to Avoid

Treating volume bushels as market bushels

Volume bushels measure space. Convert to weight only with a density you measured, then divide by the standard weight for market bushels.

Measuring the depth at the centre of a peaked bin

Enter the depth where the grain meets the wall as H and the extra height at the centre as the peak h.

Using this for a hopper-bottom bin

The calculator assumes a flat floor. Use a separate method that accounts for the actual hopper geometry before estimating the whole inventory.

References

Storage Capacity for Grains, Forages and Liquids (C6-82) (opens in a new tab), Iowa State University Extension and Outreach — Round-bin geometry and average grain depth H + h/3 for a central peak; its approximate crop capacity factors are not used as measured bulk density here.
Handbook 44, Appendix C: General Tables of Units of Measurement (opens in a new tab), National Institute of Standards and Technology — US struck bushel: exactly 2150.42 cubic inches, converted here to 0.03523907016688 m³.
Weights, Measures, and Conversion Factors for Agricultural Commodities and Their Products (opens in a new tab), USDA Economic Research Service — Commodity weight conversions, including 56 lb per bushel of shelled corn; standard weights define market units, not measured bin density.

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