Mold Risk Calculator

The calculator uses a different critical RH threshold per surface: 65% for organic materials like wood and drywall, 75% for semi-porous surfaces like concrete and plaster, and 85% for non-porous surfaces like metal and glass. It then measures how far your actual RH sits above that specific threshold — 60% RH is already 0 points from an organic threshold's risk zone edge but would need to climb further before threatening a non-porous surface, since porous organic materials absorb and retain moisture far more readily.

Dew point is computed independently via the Magnus formula (γ = ln(RH/100) + bT/(c+T), solved for temperature) and represents the surface temperature at which condensation would start forming, regardless of the risk score. If any surface in your space — a cold window, an uninsulated pipe — is at or below that dew point temperature, it will collect condensation even if the bulk air's mold risk score is low, since condensation is a localized surface phenomenon the overall risk score doesn't capture.

Ventilation quality acts as a multiplier on the combined humidity and temperature risk factors, ranging from 1.5x for poor/enclosed spaces down to 0.5x for active dehumidification. Better ventilation doesn't change the RH or temperature values you entered, but the model assumes it prevents moisture from stagnating and accumulating at surfaces, which is why it scales down both the risk level and the estimated mold onset time even when your other inputs are unchanged.

No — this calculator only models current environmental conditions (humidity, temperature, surface type, ventilation) as inputs to future growth risk. It assumes an organic nutrient source is present and has no way to detect whether mold already exists from a past leak, hidden moisture intrusion, or standing water; a low score describes the air right now, not the history of what's already happened in your space.