Grain bin calculator
YOUR BIN
| ⌀ | 18 ft | 21 ft | 24 ft | 27 ft |
|---|---|---|---|---|
| 18 ft | 3,681 | 4,294 | 4,908 | 5,521 |
| 24 ft | 6,544 | 7,634 | 8,725 | 9,816 |
| 30 ft | 10,225 | 11,929 | 13,633 | 15,337 |
| 36 ft | 14,723 | 17,177 | 19,631 | 22,085 |
| 48 ft | 26,175 | 30,537 | 34,900 | 39,262 |
Capacity and value
Cylinder = π × r² × hPeaked cone = ⅓ × π × r² × (r × tan 25° or 28°)Hopper cone = ⅓ × π × r² × (r × tan θ)Bin bu = ft³ × 0.8036 × (1 + pack%)Market bu = Bin bu × test weight ÷ standard lbShrink % = (Moist In − Target) × shrink per pointWater shrink % = (Moist In − Target) × 100 ÷ (100 − Target)Dry Bu = Wet market Bu × (1 − Shrink%)Drying Cost = Pts to dry × $/pt × Wet market BuPlain setting: 25° peak, no pack. Dealer setting: 28° peak, 6% pack. Grain depth is eave height minus the aeration floor. Shrink per point defaults to 1.3.
How to use this grain bin calculator
Enter your bin diameter and eave height (or length, width, and depth for rectangular storage), choose your crop, and the calculator shows total bushel capacity, weight, and, if you enter a market price, estimated net value after moisture shrink and drying costs. The depth slider lets you model a partially filled bin. Use the Hopper option for bins with an inverted-cone floor; the calculator automatically adds the hopper cone volume to your total.
Why a dealer chart reads higher
Dealer charts like GSI’s count a 28° peak and 6% pack, and GSI counts grain from the top of a 12 in aeration floor. This page’s plain setting counts a 25° peak and no pack, so a chart reads about 5 to 6.5% higher for the same bin. Pick “Match my dealer’s chart” and put in the floor height to count it their way. Here are three real bins.
Check three real bins against the dealer charts
| Bin | Eave | Dealer chart | Dealer setting | Plain setting |
|---|---|---|---|---|
| GSI 30 ft, 9 rings | 24 ft 2 in, 12 in floor | 15,337 | 15,550 (+1.4%) | 14,484 (−5.6%) |
| GSI 36 ft, 12 rings | 32 ft 2 in, 12 in floor | 29,404 | 29,789 (+1.3%) | 27,782 (−5.5%) |
| Brock 48 ft, 8 rings | 21 ft 6 in | 39,053 | 39,697 (+1.6%) | 36,689 (−6.1%) |
Dealer chart bushels and eave heights are as printed on GSI’s 40-Series chart and Brock’s farm bin chart. The other two columns are this page’s formula on the same bins, peaked. With the dealer setting it lands within 2% of all three. The charts don’t say exactly how they trim the peak or round the pack, so expect a small gap.
How moisture shrink works
Grain delivered above standard moisture loses weight, and value, when it is dried. The usual shrink formula is (Moisture In − Target Moisture) × 1.3, where the target defaults to the crop’s standard moisture. Part of that is water and part is handling loss. Water alone is 100 ÷ (100 − target) per point, 1.183 at 15.5% (Purdue NCH-61). Corn at 18% going into a 15.5% market shrinks 3.25%, about 98 bushels on 3,000 bushels (about three semi loads). Of the 3.25%, 2.96% is water and 0.29% is handling. Drying is charged on the wet bushels you bring in, so enter your cost per point per wet bushel to see the net value after shrink and drying. Check local cash bids →
Common Questions
- How many bushels in a 30-foot bin?
- A 30×24 ft round bin holds about 13,600 bu level-fill (1 bu = 1.244 ft³). Add a peaked cone surface for ~14,950 bu. Counted the way dealer charts do (28° peak, 6% pack) it is about 16,050 bu.
- What is the grain shrink formula?
- Shrink % = (moisture in minus standard moisture) times a factor. Corn is commonly figured at about 1.2 to 1.4 per point. Water alone is 1.183 per point drying to 15.5% (Purdue NCH-61); the rest is handling loss. This page defaults to 1.3, lets you edit it and shows the split.
- What is pack factor?
- Grain settles under its own weight, so a bin holds more bushels than its volume says. Dealer charts count 6%. Real pack depends on bin size, grain depth, moisture and test weight. The WPACKING method in ASABE EP413.2 predicts it, and in field checks of 51 corn bins it came within 0.9% of the measured grain on average (Bhadra et al. 2015). Leave it at 0 for a conservative number.
- Hopper bottom vs. flat floor?
- A hopper bin’s cone stores grain below the cylinder, so for the same wall height it actually holds a bit more than a flat floor. The calculator adds that cone volume. Hoppers are chosen for gravity unloading (no sweep auger), usually at smaller diameters.
- What size bin do I need for 50,000 bushels?
- Counted the way dealer charts do (28° peak, 6% pack), a 48-ft bin with 11 rings of 32 in (29 ft 4 in eave) holds about 51,800 bu. Level full with no pack, the same 48-ft bin needs 13 rings of 32 in (34 ft 8 in) or 10 rings of 44 in (36 ft 8 in). Use the “Sizing new storage” box above with your ring height.
- How do I figure drying cost?
- Multiply points to dry × $/pt × wet bushels. Dryers charge on the wet bushels you bring in. Drying from 18% to 15.5% = 2.5 pts. At $0.035/pt: 2.5 × $0.035 = $0.0875 per wet bu, or $262.50 on 3,000 wet bu.
Sources
- Dealer basis: GSI 40-Series bin capacity chart, “based on 28 degree angle of repose and 6% compaction factor,” capacities with a 12 in plenum. GSI producer brochure (PDF). Brock farm bin capacity chart for the 48 ft bin.
- Pack: ASABE EP413.2, the WPACKING method. Bhadra, Turner, Casada and others, “Pack factor measurements for corn in grain storage bins,” Transactions of the ASABE 58, 2015. doi:10.13031/trans.58.11033
- Water shrink and handling loss: Purdue Extension NCH-61.
- Drying charged per point per wet bushel: Iowa State Extension, Grain drying considerations this fall.
- Corn storage moisture: SDSU Extension.
- Ring heights: GSI 32 in rings (9 rings = 24 ft 2 in, 12 rings = 32 ft 2 in on its chart); Sukup 44 in sidewall sheets.
- 1 US bushel = 2,150.42 cubic inches = 1.2445 ft³.