Calculating your dew point (approx.) is straightforward once you know the Dew Point formula and what each input means. This guide explains the method in plain language, walks through a manual calculation, and gives worked examples you can follow — then you can do it instantly with the Dew Point Calculator.
What is Dew Point?
The Dew Point calculation tells you your dew point (approx.) from a few simple inputs. The figure you are solving for here is the dew point (approx.).
The Dew Point formula
The core formula is:
Dew point (approx.) = Air temperature - (100 - Relative humidity) ÷ 5Here is what each input means:
- Air temperature — a value measured in °C. Example: 25 °C.
- Relative humidity — a percentage, such as an annual rate. Example: 6%.
How to calculate it step by step
- Write down the air temperature (for example, 25 °C).
- Write down the relative humidity (for example, 6%).
- Apply the formula above to get your dew point (approx.).
- Double-check the result with the Dew Point Calculator.
Worked examples
Example 1
| Input / Output | Value |
|---|---|
| Air temperature | 25 °C |
| Relative humidity | 6% |
| Dew point (approx.) | 17.0 |
With air temperature of 25 °C and relative humidity of 6%, the dew point (approx.) works out to 17.0.
Example 2
With air temperature of 50 °C and relative humidity of 6%, the dew point (approx.) works out to 42.0.
| Result | Value |
|---|---|
| Dew point (approx.) | 42.0 |
Example 3
With air temperature of 13 °C and relative humidity of 6%, the dew point (approx.) works out to 5.0.
| Result | Value |
|---|---|
| Dew point (approx.) | 5.0 |
Tips for an accurate result
- Keep your units consistent — mixing, say, months with years or grams with kilograms is the most common source of error.
- Round only at the very end. Rounding inputs early can shift the final answer noticeably.
- Re-run the numbers whenever an input changes, rather than estimating from an old result.
Prefer not to do the maths by hand? — the Dew Point Calculator does it instantly, for free, with the formula and a worked example built in.
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