How to use the dew point from rh calculator
Prepare the values for this calculation
Estimate dew point from dry-bulb temperature and relative humidity using the Magnus approximation. Use the formula below to check that it answers your question. Read the input units before transferring figures from a statement, measurement or dataset.
Enter and check each input
- Dry-bulb temperature (°C): enter a value at least -80 and no more than 60. Use the unit named in the label or selected above. Do not leave this required field blank.
- Relative humidity (%): enter a value at least 0.0001 and no more than 100. Use the unit named in the label or selected above. Do not leave this required field blank.
The input table gives a complete example. Keep units and time periods consistent across related fields.
Calculate and resolve any input error
Choose Calculate after entering the values. Changes also update the answer after a short pause. If an error appears, follow its message, correct the field and calculate again. Reset restores the example values.
Interpret the answer
Check Dew point first. With the unchanged example inputs, it is 9.261107 °C. Interpret it using the formula and assumptions on this page.
Compare and keep a useful result
For a controlled comparison, keep every other example input unchanged and change Dry-bulb temperature (°C) from 20 to 22. The resulting Dew point is 11.100565 °C. This illustrates the equation’s response to that input, rather than a forecast of real events.
Read the chart’s axis labels and data table. A scenario curve changes one stated input while holding the others fixed; it does not add external observations. Use Download graph to save an available chart as a PNG.
Use Copy result or Download CSV to keep the answer. Share tool shares the page address without placing your input values in the URL. Recheck inputs and assumptions before using the result for a decision.
Dew Point from RH Calculator formula
γ=ln(RH/100)+aT/(b+T); Td=bγ/(a−γ).
Inputs and units
| Input | Format / range | Example |
|---|---|---|
| Dry-bulb temperature (°C) | minimum -80; maximum 60 | 20 |
| Relative humidity (%) | minimum 0.0001; maximum 100 | 50 |
Worked example
Using the example inputs above, the dew point is 9.261107 °C.
- Dew point
- 9.261107 °C
Results and assumptions
Magnus-form approximation; accuracy degrades outside ordinary atmospheric ranges.
Fix an input or unexpected result
Dry-bulb temperature (°C) is required. Enter dry-bulb temperature (°c) using the format and bounds in the input table. Zero and an empty field are different: use zero only if it is allowed and represents your data.
If your answer differs from the example, choose Reset and compare every field, including selected units and options. Check percentage versus decimal entry and whether values describe the same period. Round only the final displayed answer when reproducing the formula.
If a discrepancy remains, report the calculator issue with the page address, non-sensitive example inputs, actual result, expected result and a reference for your calculation.