Estimate grain in a round bin from bin diameter, grain depth, and center peak, with results in bushels, cubic feet, pounds, and short tons.
Advanced options
How to use our Grain Bin Calculator
- Enter Bin diameter (ft) by measuring straight across the bin through the center.
- Enter Grain depth at wall (ft) for the grain height where it touches the wall, then enter Extra height at center (ft) for how much higher the middle is. Use 0 if the top is flat.
- Choose Grain type. If you know your local bushel weight, open Advanced options and fill in Custom test weight (lb per bu).
- Click Calculate to see Estimated grain amount, Estimated weight, Grain volume, and Average grain depth used.
- Sanity-check the result by comparing Average grain depth used to your field measurements. It should be close to the wall depth, plus only part of the center peak, not the full center height across the whole bin.
Definitions
Bin diameter (ft): The full width of the round bin, measured straight across the center.
Grain depth at wall (ft): The grain height where the grain touches the sidewall.
Extra height at center (ft): How much higher the grain is in the middle than at the wall. A flat top uses 0.
Average grain depth used: The depth the calculator uses for volume. With a peak, it equals wall depth plus one-third of the extra center height.
Grain volume (ft3): Space filled by grain in cubic feet.
Estimated grain amount (bu): Grain volume converted to U.S. bushels using about 1.24446 cubic feet per bushel [3].
Custom test weight (lb per bu): Your own pounds-per-bushel value, used instead of the standard value for the selected grain.
Estimated weight: Bushels multiplied by a pounds-per-bushel value for the selected grain or your custom test weight [4].
Short tons: Pounds divided by 2,000.
Common mistakes and quick fixes
Mistake: Entering the highest center point as Grain depth at wall (ft) .
Fix: Put the wall measurement in Grain depth at wall (ft) and only the extra middle rise in Extra height at center (ft) .
Mistake: Typing the bin radius instead of the full Bin diameter (ft) .
Fix: Use the full width across the bin through the center for Bin diameter (ft) .
Mistake: Leaving an old number in Custom test weight (lb per bu) and forgetting it overrides Grain type .
Fix: Clear Custom test weight (lb per bu) if you want the standard weight for the selected Grain type .
Mistake: Treating Packed estimate as the main answer for grain actually in the bin.
Fix: Use Estimated grain amount as the main measured estimate. Use Packed estimate only as a comparison when you turn on Include 6% packed estimate .
Mistake: Assuming Estimated weight is exact for selling or hauling limits.
Fix: Read Estimate note and use a measured scale weight when the exact pounds matter.
Limitations & Key Assumptions / Boundary Conditions
- This calculator estimates grain in a round, flat-bottom bin using diameter, wall depth, and an optional centered peak.
- It does not model hopper bottoms, roof cones, off-center peaks, uneven grain surfaces, or structural details.
- The main result is a measured-volume estimate, not a manufacturer certified capacity rating.
- If you use Full bin to eave, the result still follows the same simple geometry method and depends on the depth you enter.
- Estimated weight depends on standard bushel test weights or your Custom test weight (lb per bu), so actual scale weight can differ with moisture, grain condition, fines, and local grading.
- The optional 6% packed estimate is for comparison only and should not replace the default measured estimate for grain currently in the bin.
- Small measurement errors in diameter or depth can noticeably change bushels and pounds, especially in larger bins.
Methodology
How the estimate is calculated
The calculator treats the bin as a round floor area filled to an average grain depth. If the grain is peaked, it adds only part of that center rise to the average depth, not the full peak across the whole bin.
A = pi * (D / 2)^2
Here, A is floor area in square feet and D is Bin diameter (ft).
H_avg = H_wall + H_peak / 3
Here, H_avg is average grain depth, H_wall is Grain depth at wall (ft), and H_peak is Extra height at center (ft). If the top is flat, the peak term is 0.
V = A * H_avg
V is grain volume in cubic feet.
bu = V / 1.24446
This converts cubic feet to U.S. bushels using about 1.24446 cubic feet per bushel [3].
W_lb = bu * TW
W_lb is estimated pounds, and TW is the selected standard bushel weight or your custom value.
tons_us = W_lb / 2000
This converts pounds to U.S. short tons.
bu_packed = bu * 1.06
If you turn on the packed comparison, the calculator also shows a 6% higher bushel figure for side-by-side reference.
Worked example
Suppose a round bin has Bin diameter (ft) = 18, Grain depth at wall (ft) = 15, and Extra height at center (ft) = 2.
A = pi * 9^2 = 254.469 sq ft
H_avg = 15 + 2/3 = 15.6667 ft
V = 254.469 * 15.6667 = 3989.82 ft3
bu = 3989.82 / 1.24446 = 3205.24 bu
For corn at 56 lb per bushel, the estimated weight is about 179,493.69 lb, or 89.75 short tons.
Assumptions and limits
This method assumes a round flat-bottom bin and a centered conical grain peak. Real bins can differ because of uneven surfaces, compaction, grain condition, and measurement error. Use the result as an inventory and planning estimate, not as a structural or certified capacity value.