What Is a Grain Bin Drying Time Calculator?
Natural-air and low-temperature in-bin drying removes moisture slowly by pushing large volumes of ambient (or slightly warmed) air through a grain mass. This calculator applies the widely used extension-service planning rule of thumb — that drying speed scales with airflow rate in cubic feet per minute per bushel (CFM/bu) — to give you a ballpark estimate of how long the process will take.
This is a planning tool, not a substitute for actually checking grain moisture and condition during the drying season, since real weather is far more variable than any single rule of thumb.
How to Read Your Results
Estimated Drying Time
The total number of days the calculator estimates it will take to move your grain from current moisture down to your target moisture, given your airflow rate and expected weather.
Drying Time (Hours)
The same estimate converted to hours, useful for comparing against fan run-time logs.
Estimated Drying Rate
How many moisture points per day the calculator expects to remove, based on your airflow and weather multiplier.
Moisture Points to Remove
The simple difference between your current moisture and target moisture — the total drying job ahead of you.
Real-World Example
A bin of corn at 22% moisture needs to reach 15% for safe storage, with a fan delivering 1.5 CFM/bu under average fall drying conditions.
| Item | Value |
|---|---|
| Points to remove | 7.0 points |
| Drying rate | ≈1.13 points/day |
| Estimated drying time | ≈6.2 days |
If cool, humid weather moves in instead of average conditions, that same fan could take closer to 10 days — which is why it pays to check moisture directly rather than relying only on a calendar estimate.
Tips for In-Bin Drying
- Higher CFM/bu dries faster but costs more in fan electricity — balance speed against operating cost.
- Warm, dry air removes moisture much faster than cool, humid air at the same airflow rate.
- Core the bin after filling to remove fines and improve even airflow.
- Check moisture at several depths regularly rather than assuming the whole bin dries evenly.
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Last updated: August 2026 · Reviewed by: Simple Calculator Tools Editorial Team