Free indoor humidity tool

Review indoor humidity and calculated dew point.

Enter a hygrometer reading to review indoor humidity and the calculated dew point, compared against EPA's general 30 to 50 percent indoor range. The result is environmental context, not a mold, exposure, health, or occupancy score.

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How it works

Enter measured conditions

Use temperature and relative humidity from a reliable indoor hygrometer, then choose the room only to label your record.

Calculate context

The tool calculates dew point and absolute humidity. It compares relative humidity with EPA's general 30 to 50 percent indoor range.

Document the reading

Repeat readings at different times and locations, note accessible moisture conditions, and export a summary for your records.

Enter your indoor reading

Use a reliable indoor hygrometer and follow its instructions.
Room label
Above EPA target
55%
Measured RH · calculated dew point · absolute humidity
Move a slider to update the environmental context.
Important: This calculator does not confirm mold, identify a water source, predict growth, measure exposure, assess health risk, inspect a building, or determine safe occupancy. A calculated dew point is not a surface measurement.
What dew point can and cannot tell you+

Dew point is calculated from air temperature and relative humidity. Air can reach saturation where an actual surface is at or below that temperature.

This tool does not measure surfaces. Surface temperatures vary with location, weather, insulation, airflow, materials, and nearby moisture.

One reading is limited. Repeat measurements at different times and locations. Document accessible leaks, condensation, standing water, and wet materials without opening equipment or entering unsafe spaces.

Follow equipment manufacturers and use a qualified HVAC or building professional for persistent humidity, concealed moisture, equipment concerns, or unsafe access.

FAQ

What indoor humidity range does EPA generally recommend?

EPA advises keeping indoor relative humidity between 30 and 50 percent when possible. That is general moisture-control guidance, not a guarantee that mold is absent or a personal health threshold.

Can a humidity reading confirm mold or predict when it will grow?

No. Relative humidity is one environmental measurement. It cannot confirm mold, identify hidden growth, locate a water source, or predict a specific growth time.

How should I measure indoor humidity?

Use a reliable indoor hygrometer, follow its instructions, place it away from direct moisture, vents, and windows, and repeat readings at different times and locations.

What does the calculated dew point mean?

Dew point is the temperature at which air can reach saturation. Condensation can occur where an actual surface is at or below that temperature, but this calculator does not measure any surface.

What should I do with a persistently high reading?

Confirm the reading, document accessible moisture conditions, follow equipment manufacturers, and use a qualified HVAC or building professional for persistent humidity, concealed moisture, or equipment concerns.