What Your Humidity Percentage Means
A reading on its own doesn't tell you what to do. Here's what the EPA's published indoor relative-humidity (RH) guidance actually says, and where the mold-risk threshold sits.
EPA's published indoor RH guidance
| Relative humidity | What it generally means |
|---|---|
| Below ~30% | Often too dry -- static, dry skin/sinuses, cracking wood furniture. |
| 30-50% | The range the EPA calls the ideal target (see source below). |
| Above 50%, up to 60% | Below the EPA's stated ceiling, but not the ideal range -- worth monitoring. |
| Above 60%, sustained | Above the EPA's stated ceiling -- the threshold this site treats as a mold-risk signal. |
Source: the EPA's A Brief Guide to Mold, Moisture and Your Home states: "If possible, keep indoor humidity below 60 percent (ideally between 30 and 50 percent) relative humidity." That is the direct source for the ranges above.
Sustained relative humidity above roughly 60% is the threshold this site treats as a real mold-risk signal -- worth acting on, not a reason to panic. A single warm-afternoon spike isn't the same as a room that stays there for days.
What to do with the number
Below the threshold: no action needed beyond normal ventilation. Above it, consistently: decide between active removal and a passive solution at Do You Need a Dehumidifier or a Moisture Absorber?