Yes. Both values must use the same pressure unit and temperature; this form labels them in hPa.
Relative Humidity Calculator
Enter your values below to get the result first, then scroll for the full explanation and guidance.
Relative humidity
50%Vapour pressures at the same temperature
Relative humidity: 50% (Vapour pressures at the same temperature)
Relative humidity is actual vapour pressure divided by saturation vapour pressure, expressed as a percentage.
Pressure ratio
Relative humidity is actual vapour pressure divided by saturation vapour pressure, expressed as a percentage.
Result snapshot
A quick visual read of the values behind this result.
Actual vapour pressure10 hPa
Saturation vapour pressure20 hPa
Recommended next checks
- →Use pressures measured or calculated for the same temperature and in the same unit.
- Actual vapour pressure
- 10 hPa
- Saturation vapour pressure
- 20 hPa
Try different values to compare results.
Enter actual and saturation vapour pressures at the same temperature to calculate relative humidity. This tool does not infer pressures from temperature readings.
Relative humidity
50%Vapour pressures at the same temperature
Relative humidity: 50% (Vapour pressures at the same temperature)
Relative humidity is actual vapour pressure divided by saturation vapour pressure, expressed as a percentage.
Pressure ratio
Relative humidity is actual vapour pressure divided by saturation vapour pressure, expressed as a percentage.
Result snapshot
A quick visual read of the values behind this result.
Actual vapour pressure10 hPa
Saturation vapour pressure20 hPa
Recommended next checks
- →Use pressures measured or calculated for the same temperature and in the same unit.
- Actual vapour pressure
- 10 hPa
- Saturation vapour pressure
- 20 hPa
Try different values to compare results.
Table of Contents
Table of Contents
About Relative Humidity Calculator
Relative Humidity Calculator helps you work through the main numbers for this topic quickly with a simple input flow and an instant result.
Use the calculator result as a practical starting point, then review the explanation and assumptions on the page if you want more context.
Relative humidity formula
Relative humidity (%) = actual vapour pressure / saturation vapour pressure x 100. Ten hPa over twenty hPa gives 50%.
Formula explained
Relative humidity
Calculate relative humidity from actual and saturation vapour pressures at the same temperature.
Formula
Relative humidity (%) = actual vapour pressure / saturation vapour pressure x 100
How the result is built
1Enter the labelled values using the stated units.
2Apply Relative humidity (%) = actual vapour pressure / saturation vapour pressure x 100.
3Read the result alongside the page assumptions and scope limits.
Example
Example: 10 hPa actual over 20 hPa saturation pressure gives 50% relative humidity.
Assumptions
- Both vapour pressures refer to the same temperature and use hPa.
- This does not derive vapour pressure from temperature or dew point.
Source basis
- US National Weather Service vapour pressure calculation
FAQ
Common questions
Trust and notes
Assumptions and important notes
This calculator is designed to give a fast estimate using the method shown on the page. Results are most useful when your inputs are accurate and the tool matches your situation.
Use the result as guidance rather than a final diagnosis or professional decision. If the result could affect health, legal, financial, or compliance decisions, verify it with a qualified source where appropriate.
- Both vapour pressures refer to the same temperature and use hPa.
- This does not derive vapour pressure from temperature or dew point.
Method
Relative humidity
Last reviewed
October 12, 2026