Calculate average drying rate, time, or initial and final moisture content. Select a moisture basis and solve mode; rate units mean percentage points per second, minute or hour.
- 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
Select the value to solve for. Rate mode divides initial minus final moisture content by elapsed time. Initial mode adds rate × time to the final content; final mode subtracts it from the initial content. Time mode divides the moisture change by the signed nonzero rate and requires a positive elapsed time. Use one consistent moisture basis: wet basis is 0–100%; dry basis may exceed 100%.
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. A moisture-content change is measured in percentage points, while a relative percentage change uses the initial content as its denominator. Dropping from 30% to 20% changes moisture content by 10 percentage points. Over 2 hours, the average rate is 5 percentage points/hour. This does not directly give the mass of water removed.
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.
