Calculate drying rate, time, or initial and final moisture content from any three values, using seconds, minutes, hours, %/s, %/min, or %/hr.
Customize This Calculator
Build your own version. Describe what you want changed, added, or compared.
- All Construction Calculators
- Moisture Content Calculator
- Water Vapor Transmission Rate Calculator
- Evaporation Rate (Water) Calculator
Drying Rate Formula
The calculator uses a constant drying rate based on the change in moisture content over time. Moisture content is entered as a percentage, so the drying rate is expressed in percentage points per unit of time.
- DR = drying rate
- M_i = initial moisture content, in percent
- M_f = final moisture content, in percent
- t = drying time
If you leave the drying rate blank, the calculator subtracts the final moisture content from the initial moisture content and divides by time. If you leave the initial moisture content blank, it adds the total moisture loss back to the final moisture content. If you leave the final moisture content blank, it subtracts the total moisture loss from the initial moisture content. If you leave time blank, it divides the moisture loss by the drying rate.
Drying Rate Units and Result Checks
The calculator converts time and drying rate units internally, so matching units is not required. The table below shows equivalent rates.
| Drying rate | Equivalent in %/min | Equivalent in %/hr |
|---|---|---|
| 0.001 %/s | 0.06 %/min | 3.6 %/hr |
| 0.01 %/s | 0.6 %/min | 36 %/hr |
| 0.1 %/s | 6 %/min | 360 %/hr |
Use this table to check whether the result makes physical sense.
| Result | Meaning |
|---|---|
| Positive drying rate | Final moisture content is lower than initial moisture content. |
| Zero drying rate | Moisture content did not change during the time period. |
| Negative drying rate | Final moisture content is higher than initial moisture content, so the material gained moisture. |
Example Problems
Example 1: Calculate drying rate
A material starts at 40% moisture content and ends at 25% after 5 hours.
The drying rate is 3 %/hr.
Example 2: Calculate final moisture content
A product starts at 18% moisture content and dries at 0.2 %/min for 30 minutes.
The final moisture content is 12%.
FAQ
Is drying rate the same as percent moisture removed?
No. Percent moisture removed is the total change in moisture content. Drying rate includes time. For example, dropping from 30% to 20% removes 10 percentage points of moisture. If that happens in 2 hours, the drying rate is 5 %/hr.
Why does the calculator use percentage points?
The calculation subtracts one moisture percentage from another. A drop from 40% to 30% is a 10 percentage point drop, not a 10% relative decrease. The drying rate is therefore percentage points per second, minute, or hour.
Can the drying rate be negative?
Yes. A negative result means the final moisture content is greater than the initial moisture content. That usually indicates moisture gain, reversed input values, or a process that is not actually drying during the time interval entered.
