Moisture & Mold Risk Calculator
Estimate condensation risk from indoor air temperature, relative humidity, and an optional surface temperature. Useful for crawlspaces, windows, and cool exterior walls.
Temperature unit
Results
- Dew point
- 53.1°F
- Surface − dew point
- 11.9°F
- Risk band
- Low
- Surface is more than 5°F above dew point — low condensation risk from these readings.
- Surface temperature defaulted to air temperature − 5°F (typical cool wall/window offset).
Methodology
Dew point is calculated with the Magnus–Tetens approximation (temps in °C): dewPointC ≈ b · γ / (a − γ), where γ = ln(RH/100) + a·T/(b+T), a = 17.62, and b = 243.12.
Risk bands use the margin surfaceTemp − dewPoint (both in °F). If surface temperature is left blank, it defaults to air temperature − 5°F.
- Margin > 5°F — Low
- Margin 2–5°F — Moderate
- Margin 0–2°F — High
- Margin < 0°F — Condensation likely
- RH ≥ 60% also flags elevated indoor moisture concern
Educational estimate only—not a mold inspection, IAQ assessment, or professional diagnosis. Real conditions depend on measurement accuracy, airflow, and building assemblies.