Home Humidity & Condensation Checker

Enter room temperature and relative humidity. If you also know the surface temperature of a window or wall, the checker can show whether that surface is at or below the estimated dew point.

Room temperature (°C)Relative humidity (%)Window/wall surface temperature (°C)

Humidity bandHigh

Estimated dew point13.2°C

Surface condensation checkCondensation possible

This does not diagnose damp. It only compares a humidity-derived dew point with the surface temperature you entered.

What the result means

Humidity readings vary by sensor placement and calibration.
A single reading is less useful than a pattern measured over several days.
This tool is informational and does not diagnose building defects.

Related guides

Read more about the topics covered by this calculator:

Best humidity level for a UK home

How this calculator works

Formula

Dew point from Magnus formula; condensation risk = surface temperature ≤ dew point

Inputs

Room temperature in °C
Relative humidity in %
Window or wall surface temperature in °C (optional)

Outputs

Humidity band (Low/Moderate/High/Very high)
Estimated dew point
Surface condensation check result

Assumptions

Uses the Magnus formula for dew point estimation.
Humidity readings vary by sensor placement and calibration.
A single reading is less useful than a pattern measured over several days.

Example calculation

At 20°C, 65% RH and a window surface at 12°C: dew point is ~13.1°C, surface is below dew point, so condensation is possible on that window.

Tariff source

N/A — this calculator does not use energy rates.

Limitations

This tool is informational and does not diagnose building defects.
Sensor accuracy varies; cheap hygrometers can be several percent off.
Persistent damp may have structural causes that a humidity reading cannot identify.