Grain Bin Calculator
Enter your bin dimensions to find storage capacity in bushels and total grain weight. Choose round or rectangular, add a peaked roof or hopper, pick your grain type, and switch between imperial and metric. Results update instantly as you type.
How to calculate grain bin capacity in bushels
Grain bin capacity is calculated by finding the interior volume of the bin and converting it to bushels. One Winchester bushel equals 1.2445 cubic feet, so the conversion factor is 1 divided by 1.2445, which is about 0.8036 bushels per cubic foot. For a round (cylindrical) bin, the sidewall volume is pi times the radius squared times the sidewall height. If the bin has a peaked conical roof, its volume is one-third times pi times the radius squared times the roof height. A hopper bottom adds another cone. Add all three sections and multiply by the bushel conversion factor to get total capacity. For a rectangular bin the sidewall is length times width times height, and a peaked roof adds one-third of that footprint times the peak height.
Grain type and test weight
Test weight is the weight of one Winchester bushel of a specific grain, established by the USDA. Because different grains pack differently, a bushel of oats (32 lb) weighs far less than a bushel of soybeans (60 lb) even though the volume is identical. This calculator applies the official USDA test weight for the selected grain to convert bushel volume into pounds and short tons. Corn at 56 lb/bu is the most common storage commodity; wheat, soybeans, rye and sorghum share the 56-60 lb range, while oats (32 lb) and sunflower (25 lb) are much lighter. If your grain has a non-standard test weight due to moisture or quality, the actual weight will differ from this estimate.
Peaked roofs and hopper bottoms
A peaked (conical) roof adds usable volume above the eave line. Filling grain into the cone makes efficient use of space but also piles grain above the intended design load, so most bins are designed to be overfilled only partially into the peaked section. A hopper-bottom bin has an inverted cone at the base that allows gravity unloading. That cone holds grain but is typically not counted as separately manageable storage, so this calculator includes it in total volume. Many flat-bottom bins use augers or sweep systems rather than a hopper. The sidewall height refers to the straight vertical portion only, from the floor or hopper outlet to the eave.
Partial fill and aeration planning
The fill-level input lets you estimate the weight and bushel count at any point during loading or draw-down. This matters for structural loading calculations, since most grain bins are rated at or below their rated capacity. Aeration systems push or pull air through stored grain to maintain temperature and prevent moisture migration. A common rule of thumb is to size aeration fans for 0.1 cubic feet of air per minute per bushel (cfm/bu) for maintenance aeration, and 0.2 cfm/bu or more for rapid drying. Knowing exact bushel counts at various fill levels helps match fan capacity to the actual grain mass in the bin.
USDA standard grain test weights
| Grain | Test weight (lb/bu) | Metric equivalent (kg/hl) |
|---|---|---|
| Corn | 56 | 71.9 |
| Soybeans | 60 | 77.1 |
| Wheat (hard or soft) | 60 | 77.1 |
| Wheat (durum) | 60 | 77.1 |
| Rye | 56 | 71.9 |
| Sorghum | 56 | 71.9 |
| Barley | 48 | 61.7 |
| Rice (rough) | 45 | 57.8 |
| Dry beans | 60 | 77.1 |
| Oats | 32 | 41.2 |
| Sunflower | 25 | 32.1 |
Official test weights used to convert bushel volumes to grain mass. Source: USDA Grain Inspection Handbook.
Frequently asked questions
How many bushels does a 30-foot diameter grain bin hold?
A round bin with a 30-foot diameter and a 24-foot sidewall holds about 16,200 bushels of cylindrical space before adding any roof cone. With a 6-foot peaked roof, the total rises to roughly 17,900 bushels. Actual capacity depends on the exact sidewall height and roof geometry. Enter your specific dimensions in the calculator above for a precise result.
What is the conversion factor from cubic feet to bushels?
One Winchester bushel (the standard US agricultural bushel) equals 1.2445 cubic feet, so you multiply cubic feet by 0.8036 to get bushels. For example, 1,000 cubic feet of space holds about 804 bushels. This calculator applies that conversion automatically.
Does grain type affect how many bushels fit in the bin?
No, the number of bushels the bin holds does not change with grain type - a bushel is a fixed volume. However, grain type does affect the total weight. A full bin of oats at 32 lb/bu weighs far less than the same bin full of soybeans at 60 lb/bu. The grain type selector here is used only to calculate weight, not bushel count.
How do I calculate the capacity of a bin with a hopper bottom?
A hopper-bottom bin is a cylinder on top with an inverted cone below. The total usable volume is the cylinder volume (pi times radius squared times sidewall height) plus the cone volume (one-third times pi times radius squared times hopper height). Convert the sum to bushels by multiplying by 0.8036. This calculator handles that automatically when you select "Has hopper" and enter the hopper height.
How do I convert grain bin bushels to metric tonnes?
Multiply the filled bushels by the grain test weight in pounds per bushel, divide by 2,204.6 to get metric tonnes. For corn (56 lb/bu): 10,000 bu times 56 lb equals 560,000 lb, divided by 2,204.6 equals about 254 metric tonnes. The calculator gives you weight in pounds and short tons; divide short tons by 1.102 to convert to metric tonnes.
What is the difference between eave height and total bin height?
Eave height (also called sidewall height) is the vertical distance from the floor to the point where the sidewall meets the roof. Total bin height includes the additional roof peak. For a 24-foot eave bin with a 6-foot peaked roof, total height is 30 feet but the sidewall-only capacity calculation uses 24 feet. This calculator separates the two to give you accurate volumes for each section.