Grain Bin Calculator

Calculate grain bin capacity, volume, bushels, and total weight

Enter your grain bin dimensions to estimate storage capacity and grain weight for round or rectangular bins.

Last updated: June 17, 2026

CreatorFrank Zhao

Grain bin dimensions

Grain bin type

Roof

Diameter

Radius

Sidewall height

The grain bin has a hopper

Grain weight

Volume and weight results

Volume of grain

Grain volume in bushels

Total grain weight

1Round body volume

V_b = \pi r^2 h

2Rectangular body volume

V_b = L W h

3Conical roof volume

\text{Round: } V_r = \frac{1}{3} \pi r^2 h_r

\text{Rectangular: } V_r = \frac{1}{3} L W h_r

4Curved roof volume

\text{Round: } V_r = \pi r^2 \left(\frac{2}{3}r + h_r\right)

\text{Rectangular (precise): } V_r = L \left[ r_a^2 \cos^{-1}\!\left(\frac{r_a-h_r}{r_a}\right) - (r_a-h_r)\sqrt{2r_a h_r-h_r^2} \right]

\text{where } r_a = W/2 \text{ (arch radius)}

5Hopper volume

V_h = \frac{1}{3} \pi r^2 h_h

Rectangular hopper not yet supported

6Bushels conversion

B = V \times 0.7786

7Total weight

W = V \times \rho

VTotal volume

VbBody volume

rBin radius

hSidewall height

LBin length

WBin width

hrRoof height

hhHopper height

BBushels (Bu)

ρGrain density

WTotal weight

VrRoof volume

Knowing how much grain your bin holds is one of those numbers you don't want to guess at — overestimate and you might run out of storage mid-harvest, underestimate and you could leave money on the table. This guide walks you through the calculator, gives real examples, and explains the math behind the numbers.

→Introduction / overview
→How to use (quick start)
→Step-by-step examples
→Real-world use cases
→Common scenarios
→Tips & best practices
→Calculation method / formulas
→Related concepts
→FAQs
→Limitations & sources

Introduction / overview

The Grain Bin Calculator is a practical tool that tells you exactly how much grain your bin can hold — in cubic meters, cubic feet, bushels, and total weight. It works for both round bins (the classic silo shape) and rectangular bins (common in flat storage or warehouse setups).

If you are a farmer, grain trader, or elevator operator, this calculator helps you answer the key question: “How many bushels do I have, and what’s that worth?”

Who is this for?

Farmers and growers who need to estimate storage capacity before or during harvest.
Grain elevator and co-op operators managing multiple bins and tracking inventory.
Agronomists and crop advisors helping clients plan storage needs.
Students and researchers studying grain storage, post-harvest handling, or agricultural engineering.

The calculator uses standard geometric volume formulas and a standard bushel conversion ( $1\ \mathrm{bu} = 1.244\ \mathrm{ft}^3$ of grain). It supports optional conical and curved roofs, as well as a hopper (conical bottom) for round bins, so you can get a realistic total capacity — not just the straight-wall volume.

How to use / quick start

1Choose your bin type — Round or Rectangular. Most grain bins on farms are round, but flat warehouses and bunker storage are usually rectangular.
2Enter the dimensions: for round bins, provide the diameter (the radius auto-fills); for rectangular bins, provide length and width. Then enter the sidewall height.
3Add optional features: if your bin has a conical or curved roof, enter the roof height. For round bins with a hopper (cone bottom), check the hopper box and enter the hopper height.
4Enter the grain weight (test weight) — this is the density of the specific grain. Common values: wheat ~770 kg/m³, corn ~720 kg/m³, soybeans ~770 kg/m³.
5Read your results — volume, bushels, and total grain weight appear in the “Volume and weight results” section. You can edit any result to reverse-calculate the corresponding dimension (a handy feature if you know your bin's capacity but are unsure of a dimension).

How to interpret results

Volume — the total space inside your bin (including roof and hopper if specified). Use this to understand how much physical space the grain occupies.
Bushels — the standard grain trade unit. In the US, grain is typically bought and sold by the bushel.
Total weight — the actual mass of grain. Useful for trucking limits, floor load ratings, and inventory tracking.

Step-by-step example calculations

Example 1: Round bin with corn

You have a round grain bin with a diameter of $7.32\ \mathrm{m}$ (24 ft), a sidewall height of $4.27\ \mathrm{m}$ (14 ft), and a conical roof with a height of $2.44\ \mathrm{m}$ (8 ft). You are storing corn with a test weight of $720\ \mathrm{kg/m^3}$ . No hopper.

r = \frac{d}{2} = \frac{7.32}{2}

=

3.66\ \mathrm{m}

V_{\text{body}} = \pi r^2 h

=

\pi (3.66)^2 (4.27)

\approx

179.5\ \mathrm{m}^3

V_{\text{roof}} = \frac{1}{3}\pi r^2 h_r

=

\frac{1}{3}\pi (3.66)^2 (2.44)

\approx

34.2\ \mathrm{m}^3

V_{\text{total}} = 179.5 + 34.2

=

213.7\ \mathrm{m}^3

\text{Bushels} = \frac{213.7}{0.0283168} \times 0.7786

\approx

5,\!875\ \mathrm{bu}

\text{Weight} = 213.7 \times 720

=

153,\!864\ \mathrm{kg}

\approx

154\ \mathrm{metric\ tons}

Interpretation: this bin holds roughly 5,875 bushels of corn, weighing about 154 metric tons. At current corn prices, that is a valuable storage asset. After calculating your bin capacity, you might also estimate your field’s yield using an Acreage Calculator to see if your bins are large enough for the upcoming harvest.

Example 2: Rectangular bin with wheat

You have a rectangular flat storage building: $30.5\ \mathrm{m}$ long, $12.2\ \mathrm{m}$ wide, with a grain depth of $3.05\ \mathrm{m}$ . Wheat test weight: $770\ \mathrm{kg/m^3}$ .

V = L \times W \times h

=

30.5 \times 12.2 \times 3.05

\approx

1,\!135\ \mathrm{m}^3

\text{Bushels} = \frac{1,\!135}{0.0283168} \times 0.7786

\approx

31,\!200\ \mathrm{bu}

\text{Weight} = 1,\!135 \times 770

\approx

874,\!000\ \mathrm{kg}

\approx

874\ \mathrm{metric\ tons}

That is about 31,200 bushels of wheat — a solid-sized flat storage. Keep in mind that wheat is denser than corn, so the same volume holds more weight. For managing livestock alongside your grain operation, check out our Animal Mortality Rate Calculator to monitor farm health metrics.

Real-world examples / use cases

1) Pre-harvest storage planning

Background: A corn grower expects 200,000 bushels from 400 acres. They have three round bins and need to check if total capacity is sufficient.

Inputs: Measure each bin’s diameter and height, enter the dimensions, add roof heights. Sum the bushel results.

Result: If total capacity is 185,000 bushels, the farmer knows to arrange temporary storage or schedule earlier deliveries to the elevator.

2) Truck weight compliance

Background: A grain hauler needs to load a semi-trailer without exceeding the $36,\!300\ \mathrm{kg}$ (80,000 lb) gross vehicle weight limit.

Inputs: Use the calculator’s bushel-to-weight feature. For soybeans at $770\ \mathrm{kg/m^3}$ , each bushel weighs about $27.2\ \mathrm{kg}$ .

Result: The legal load is roughly 1,100 bushels of soybeans. The driver can confidently load to that limit without scale-ticket guesswork.

3) Bin construction sizing

Background: A farmer is buying a new bin and wants to know what size will hold 50,000 bushels of wheat.

Inputs: Use the reverse-calculation feature. Enter the target bushels, and the calculator will show the required height for a given diameter.

Result: Try different diameter/height combinations until the bushel target is met, then choose the most cost-effective option. When planning construction, our Board Foot Calculator can help estimate lumber needs for any wood components.

4) Grain inventory tracking

Background: An elevator operator manages 15 bins and needs to track inventory between incoming loads and outgoing shipments.

Inputs: For each bin, save the dimensions. When grain depth changes (e.g., after a shipment), update the height — the calculator instantly recalculates remaining bushels.

Result: Real-time inventory tracking without climbing bins or relying solely on flow meters. Any discrepancy between calculated and actual may indicate bridging, spoilage, or measurement error.

Common scenarios / when to use

Harvest season planning

Estimate total bin capacity before harvest begins so you know whether you need temporary storage or early elevator deliveries.

Field yield estimation

After combining a field, compare the actual bin fill level against your expected yield to spot discrepancies early.

Bin sizing for new builds

Use the reverse-calculation mode to determine what diameter and height you need to hit a specific bushel capacity target.

Flat storage management

Rectangular warehouses and bunkers are common for long-term storage. Calculate usable capacity based on grain depth and floor dimensions.

Buying or selling grain

When negotiating a price, convert your volume to bushels and weight quickly so you know exactly what you are trading.

Comparing grain types

Different grains have different test weights. Compare how many bushels of corn vs. soybeans vs. wheat your bin holds at the same volume.

When the calculator may be less accurate

The grain surface is not level (e.g., peaked or bridged) — the volume formula assumes a flat grain surface.
The bin has internal structures (ladders, supports, sumps) that displace grain — actual capacity will be slightly less.
Test weight varies with moisture content — wet grain is heavier but shrinks as it dries.

Tips & best practices

1
Measure at multiple points and average
Bins are rarely perfectly round or perfectly plumb. Measure the diameter in at least two directions (east-west and north-south) and average them. For height, measure from the floor to the roof eave at several spots around the wall.
2
Know your grain's test weight
Test weight varies by variety, growing season, and moisture. Use a test weight kit to measure it accurately, or refer to standard values for your region. Common defaults: corn ~720 kg/m³ (56 lb/bu), wheat ~770 kg/m³ (60 lb/bu), soybeans ~770 kg/m³ (60 lb/bu).
3
Account for moisture shrink
Grain usually comes out of the field at a higher moisture than storage level. As it dries in the bin, it loses weight and volume. A corn crop at 25% moisture that dries to 15% will lose about 10-12% of its original weight. Factor this into your storage planning.
4
Use the reverse-calc feature for tricky dimensions
If you know the bin holds a certain number of bushels (e.g., a manufacturer spec), you can enter the bushel value and the calculator will work backward to find the required sidewall height. This is a great double-check for your measurements.
5
Don't forget the roof and hopper
The roof volume can add 10-20% to your bin's total capacity. If you ignore it, you are undershooting your usable storage. Similarly, a hopper bottom adds conical volume below the sidewall that is often overlooked.

Keep a grain bin log

Record each bin’s dimensions, calculated capacity, grain type, and date filled. Over several seasons, you will build a reference that helps spot trends in yield and storage efficiency.

Cross-check with scales

If your farm has a truck scale, compare scale weights to calculator estimates for a few loads. This calibrates your test weight assumption and builds confidence in the numbers.

Measure from the right reference points

Sidewall height is measured from the floor to the eave (where the roof starts), not to the peak. Roof height is from the eave to the peak. Getting these mixed up is the most common measurement error.

Plan for aeration zones

Aeration fans and ducts take up some space and affect airflow patterns. When planning fill levels, leave headspace above the grain for proper air circulation, especially for high-moisture grain.

Calculation method / formula explanation

The calculator builds total volume by adding up to three components: the body (straight-wall section), the roof (if any), and the hopper (if any).

Key variables

$r$ : bin radius, $h$ : sidewall height, $h_r$ : roof height
$L$ : bin length (rectangular), $W$ : bin width (rectangular)
$\rho$ : grain density (test weight), $B$ : bushels
$r_a = W/2$ : arch radius (rectangular curved roof)

Round body volume

V_{\text{body}} = \pi r^2 h

The standard formula for a cylinder. This is the main storage section of a round grain bin.

Rectangular body volume

V_{\text{body}} = L \times W \times h

For flat storage or rectangular bins. Simply length times width times grain depth.

Roof volume

Two roof types are supported. The formula depends on whether the bin is round or rectangular:

Conical roof:
$\text{Round: } V_{\text{roof}} = \frac{1}{3}\pi r^2 h_r$
$\text{Rectangular: } V_{\text{roof}} = \frac{1}{3} L W h_r$
A cone (round) or pyramid (rectangular) on top — common on older bins.
Curved roof:
$\text{Round: } V_{\text{roof}} = \pi r^2 \left(\frac{2}{3}r + h_r\right)$
$\text{Rectangular (precise): } V_{\text{roof}} = L \times A_{\text{seg}}$
$A_{\text{seg}} = r_a^2 \cos^{-1}\!\left(\frac{r_a-h_r}{r_a}\right) - (r_a-h_r)\sqrt{2r_a h_r - h_r^2}$
$\text{where } r_a = W/2 \text{ (arch radius spans across the width)}$
A cylindrical arch (barrel vault) on top of a rectangular bin — common in large storage facilities.

Hopper volume (conical bottom)

V_{\text{hopper}} = \frac{1}{3}\pi r^2 h_h

A hopper is a cone-shaped bottom that helps grain flow out by gravity. It adds volume below the sidewall.

Total volume

V_{\text{total}} = V_{\text{body}} + V_{\text{roof}} + V_{\text{hopper}}

Bushels conversion

One US bushel is defined as $1.244\ \mathrm{ft}^3$ of grain. In metric terms:

1\ \mathrm{bu} = 0.0283168\ \mathrm{m}^3 \div 0.7786

\text{Bushels} = \frac{V_{\text{total}}\ (\mathrm{m}^3)}{0.0283168} \times 0.7786

Total grain weight

\text{Weight} = V_{\text{total}} \times \rho

Where $\rho$ is the grain density (test weight). Multiply the total volume in cubic meters by the density in kg/m³ to get total mass in kilograms.

Accuracy comparison with other calculators

During development, we compared our calculator against other popular grain bin calculators (such as Omni Calculator's Grain Bin Calculator). We identified two common accuracy issues worth noting:

1. Rectangular curved roof: approximate vs precise formula

Some calculators use an approximate formula for a curved roof on a rectangular bin:

V_{\text{roof}} \approx L \times W \times \left(\frac{2}{3} + h_r\right)

This adds a dimensionless constant $(2/3)$ directly to a length ( $h_r$ ), which is dimensionally inconsistent and can produce significant errors for large roof heights.

Our calculator uses the precise cylindrical arch (barrel vault) formula:

V_{\text{roof}} = L \times \left[ r_a^2 \cos^{-1}\!\left(\frac{r_a-h_r}{r_a}\right) - (r_a-h_r)\sqrt{2r_a h_r - h_r^2} \right]

\text{where } r_a = W/2

Example: W=12m, L=12m, h_r=3m → Approx = 528 m³, Precise = 265 m³ (~50% error)

2. Rectangular mode incorrectly showing Diameter / Radius

Some calculators show Diameter and Radius fields even when Rectangular is selected. A rectangular bin has Length × Width, not a diameter. This is likely a UI oversight where the Round-mode fields were not hidden when switching bin types.

Our calculator correctly hides the Diameter and Radius fields in Rectangular mode and only shows Length and Width — the proper dimensions for a rectangular bin.

3. Rectangular conical roof: diameter not applicable

A conical roof on a rectangular bin is actually a pyramid (four-sided), not a cone. Its volume is correctly calculated as:

V_{\text{roof}} = \frac{1}{3} \times L \times W \times h_r

Some calculators show a diameter/radius field for this case, which suggests they are reusing the round-bin formula $\frac{1}{3}\pi r^2 h_r$ . This would compute the volume of a circular cone rather than a rectangular pyramid, giving an incorrect result for a rectangular bin.

Note: These comparisons are based on publicly available calculators as of June 2026. Calculator accuracy varies by implementation. Our goal is to provide the most physically accurate results for common grain bin geometries.

Related concepts / background info

What is a bushel, anyway?

A bushel is a unit of volume used in the US for agricultural commodities. By definition, one bushel equals $1.244\ \mathrm{ft}^3$ (about $35.24\ \mathrm{L}$ ). But here is the key: a bushel of corn does not weigh the same as a bushel of wheat. The weight depends on the grain’s test weight (density). That is why you need both volume and density to get accurate mass.

Grain	Typical test weight (lb/bu)	Typical density (kg/m³)
Corn	56	720
Wheat	60	770
Soybeans	60	770
Oats	32	410
Barley	48	620

Why test weight matters

Test weight is a measure of grain quality and density. Higher test weight means more grain mass per bushel, which usually indicates better quality, better milling yield, and more starch content. Buyers often pay a premium for high test weight grain, and may discount or reject grain that falls below standard minimums (e.g., 54 lb/bu for No. 2 yellow corn).

Roof and hopper geometry

The roof on a grain bin is not just a lid — it is additional storage space. A conical roof adds about one-third the volume of a cylinder of the same base and height. A curved or domed roof adds even more. Similarly, a hopper bottom converts the flat floor into a cone, which both adds volume and enables gravity unloading. When you include these in the calculator, you get a more realistic picture of total usable capacity.

Related tools on this site

Acreage Calculator

Calculate field size and yield per acre

Board Foot Calculator

Estimate lumber for bin construction

Frequently asked questions (FAQs)

What is the difference between a bushel and a cubic foot?

One US bushel equals $1.244\ \mathrm{ft}^3$ of grain. To convert cubic feet to bushels, divide by 1.244. The calculator handles this conversion automatically using the metric equivalent ( $0.0283168\ \mathrm{m}^3$ per bushel, adjusted with the 0.7786 factor).

Why does the calculator need the grain weight (density)?

Volume alone tells you how much space the grain occupies, but weight is what matters for trucking limits, floor load ratings, and most commercial transactions. Different grains have different densities, so you need the test weight to convert volume accurately to mass.

Can I use this for silage or other non-grain materials?

The volume calculations work for any material, but the bushel conversion and test weight values are specific to dry grain. Silage, for example, has a much higher moisture content and different density. You can still use the volume output, but you will need to supply an appropriate density value for your material.

What if my bin is not perfectly round?

Measure the diameter in several directions and use the average. If the bin is significantly out-of-round (e.g., an oval or squat silo), the cylinder approximation will have some error. For severe cases, consider measuring the circumference and calculating the effective diameter using $d = \frac{C}{\pi}$ .

How do I measure roof height correctly?

Roof height is measured from the eave (where the sidewall meets the roof) to the peak of the roof. It is not the total height from the ground to the peak, and it is not the sidewall height. If you only know the total height (ground to peak), subtract the sidewall height to get the roof height.

Does the calculator account for grain compaction?

No. Grain at the bottom of a deep bin compresses under the weight of the grain above, increasing its density slightly. This effect is small for typical bin depths (less than 2-3%) and is within the margin of measurement error. For very deep bins (over 15 m / 50 ft), consider adding 2-3% to your calculated weight.

What units can I use for input and output?

Dimensions can be entered in meters, inches, feet, or feet/inches. Volume can be displayed in cubic meters, cubic inches, cubic feet, liters, US gallons, or UK gallons. Weight supports grams, kilograms, metric tons, grains, pounds, US short tons, and imperial tons. Grain density supports kg/m³, lb/cu ft, and g/m³.

Why does changing one value update others automatically?

The calculator uses a bidirectional solving system. When you edit any input, it recalculates all related outputs. You can even edit a result field (like bushels) and the calculator will work backward to find the corresponding dimension. This is useful for “what-if” scenarios.

Limitations & disclaimers

•This calculator provides estimates only. Actual bin capacity may vary due to construction tolerances, internal structures, and grain settling.
•Results should not replace professional engineering assessments for bin construction, structural loading, or grain storage safety.
•Grain test weight varies significantly with moisture content, variety, and growing conditions. Use actual test weight measurements when precision matters.
•The bushel conversion uses the standard US bushel definition. Canadian and UK bushels differ slightly — verify which standard applies in your region.
•Always follow safe grain bin entry and handling procedures. Flowing grain can be deadly — never enter a bin while unloading is in progress.

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