Free Grain Bin Calculator

The Grain Bin Calculator is a free online tool that works as both a bushel calculator and a grain storage capacity estimator. It helps you determine the volume, weight, and number of bushels stored in a grain bin or silo, regardless of shape—round or rectangular—and whether it includes a peaked roof, curved roof, and/or hopper bottom. This grain bin capacity calculator also doubles as a grain bin size calculator: enter your desired capacity and it will guide you toward the needed dimensions, making it essential for planning dry grain storage in farming operations.

What Is a Grain Bin?

A grain bin (often called a grain silo) is a large metal container—typically made of galvanized steel—designed to protect harvested grains such as corn, soybeans, and wheat from rodents, moisture, and weather. Most bins are cylindrical because round walls are easier to clean and promote better airflow. However, rectangular flat‑storage bins are also widely used; they are simpler and cheaper to construct on a concrete foundation and are well suited for long‑term grain storage.

Many round bins feature a piled (conical) roof that allows rapid top‑filling through a central hatch, and an optional hopper bottom that uses gravity for easy emptying. Proper ventilation through the structure keeps the stored grain dry and reduces spoilage.

Grain bins come in a wide range of sizes. Small units can hold about 1,000 bushels (roughly 25.4 metric tons), while large commercial silos store up to 1 million bushels. The calculator handles any size by accepting user‑provided dimensions.

How to Use the Calculator

Using the grain bin bushel calculator involves a few simple steps:

1. Choose the bin type – select round (cylindrical) or rectangular.
2. Indicate roof and hopper – specify whether the bin has a roof (and its shape: peaked or curved) and/or a hopper bottom; provide the corresponding heights.
3. Enter main dimensions – for round bins, the radius (or diameter) and body height; for rectangular bins, the length, width, and body height.
4. Optional: test weight – if you know the grain’s test weight (bushels per pound or kg per hectoliter), the tool can calculate the total mass.

If the bin is only partially filled, simply enter the actual grain depth as the body height to estimate the current stored volume. The tool also allows you to switch between imperial and metric units, so you can work in whatever system you prefer.

Capacity Formulas

The calculator first computes the bin’s volume in cubic feet, then multiplies by the standard conversion constant $0.7786\ \text{bu/ft}^3$ to obtain bushels. The exact formula depends on the bin shape and whether extra features (roof, hopper) are present.

Round Bins

Let $R$ be the bin radius (half the diameter), $H_{\text{body}}$ the vertical side height, $H_{\text{top}}$ the height of the roof above the body, and $H_{\text{hopper}}$ the depth of the hopper cone.

• Flat‑roof, flat‑floor (body only)

  $$\text{Bushels} = \pi R^{2} H_{\text{body}} \times 0.7786$$

• Peaked (conical) roof + hopper

  $$\text{Bushels} = \pi R^{2} H_{\text{body}} \times 0.7786 + \frac{1}{3}\pi R^{2} H_{\text{top}} \times 0.7786 + \frac{1}{3}\pi R^{2} H_{\text{hopper}} \times 0.7786$$

• Curved (dome) roof + hopper

  $$\text{Bushels} = \pi R^{2} H_{\text{body}} \times 0.7786 + \pi R^{2} \left(\frac{2}{3}R + H_{\text{top}}\right) \times 0.7786 + \frac{1}{3}\pi R^{2} \left(\frac{2}{3}R + H_{\text{hopper}}\right) \times 0.7786$$

Rectangular Bins

Let $L$ be the bin length, $W$ the width, $H_{\text{body}}$ the side wall height, and $H_{\text{top}}$ the rise of the roof above the walls.

• Flat roof, flat floor

  $$\text{Bushels} = L \cdot W \cdot H_{\text{body}} \times 0.7786$$

• Peaked roof

  $$\text{Bushels} = L \cdot W \cdot H_{\text{body}} \times 0.7786 + \frac{1}{3}L \cdot W \cdot H_{\text{top}} \times 0.7786$$

• Curved roof

  $$\text{Bushels} = L \cdot W \cdot H_{\text{body}} \times 0.7786 + L \cdot W \cdot \left(\frac{2}{3} + H_{\text{top}}\right) \times 0.7786$$

Where to Find the Numbers

All bin dimensions are typically provided by the manufacturer. For planning purposes, you can also use the calculator in reverse: specify a target capacity and experiment with different dimensions until the estimated bushels match your goal—effectively turning it into a grain bin size calculator.

Important Notes

• All measurements must be in the same units (feet, inches, meters, etc.).
• The conversion factor $0.7786\ \text{bu/ft}^3$ is a standard average for dry grain. Actual bushel weight varies by grain type.
• The calculated values are estimates. They do not account for the angle of repose of the grain when filling a peaked roof or hopper, nor for compaction over time. Use them as a planning guide, and always verify with professional engineering for final structures.
• For partially filled bins, you can still get a useful estimate by entering the current grain depth as the body height.

Whether you are sizing a new storage system or checking the capacity of an existing bin, this grain storage calculator provides quick, useful estimates. It is a versatile grain silo calculator that can be adapted to almost any configuration.