There is no single correct indoor humidity, which is why the charts you find elsewhere disagree with each other. The right number depends on the season, on how cold it is outside, on which room you are standing in and on the climate you live in.
This page collects all four in one place. If you want the short version: 30–50% is the healthy band, 40–50% is the comfortable middle of it, and the winter target falls as the outdoor temperature does.
The overall range
The 30–50% band comes from the point where several risks are simultaneously near their minimum: dust mites need around 50% to thrive, mold germinates near 80% at a surface, and dry airways below 30% clear viruses less effectively.
| Reading | What it means | What to do |
|---|---|---|
| Below 25% | Static shocks, nosebleeds, cracked wood and furniture joints | Humidify — see the winter table below |
| 25–30% | Typical heated house in winter; dry skin and airways | Humidify toward 40% |
| 30–40% | Low end of healthy. Fine, and correct in a hard freeze | Acceptable |
| 40–50% | The comfortable middle | Target |
| 50–60% | Dust mites thrive; cold surfaces begin to sweat | Ventilate, watch the coldest room |
| 60–70% | Mold takes hold on cold walls and behind furniture | Dehumidify |
| Above 70% | Active mold and dust-mite risk; damage to plaster and framing | Find the source now |
Winter: the target falls with the outdoor temperature
This is the table most charts leave out, and the one that prevents the most damage. Your coldest surface follows the outdoor temperature, so the humidity you can safely hold falls as it gets colder outside.
Figures below are conservative for a typical double-glazed house. Single glazing or metal frames need lower; well-insulated triple glazing tolerates more.
| Outdoor temperature | Indoor target | If you go higher |
|---|---|---|
| Above 40 °F | 45% | Comfortable, little risk |
| 20 to 40 °F | 40% | Light morning condensation on the coldest windows |
| 10 to 20 °F | 35% | Water on the glass, wet sills |
| 0 to 10 °F | 30% | Streaming windows, frames staying wet |
| −10 to 0 °F | 25% | Ice forming on the inside of the glass |
| Below −10 °F | 20% | Ice, and frost risk in the attic from leaking air |
By room
Colder spaces need lower targets, because their surfaces reach the dew point sooner. A bathroom is the exception — it is supposed to spike, and what matters is recovery time.
| Room | Target | Why |
|---|---|---|
| Bedroom | 40–50% | Two sleeping adults add about a pint overnight |
| Bathroom | Under 60% in 20 min | Peaks past 90%; recovery is the measure |
| Kitchen | Under 60% | Second-largest moisture source in the house |
| Laundry room | Under 60% | Largest single source if the dryer vents indoors |
| Basement | 50% or below | Coldest surfaces in the building, year-round |
| Crawl space | 55% or below | Only achievable once the ground is sealed |
| Garage | 50–60% | Rust, not mold, sets the limit |
| Closet | 45–55% | Still air against the coldest wall in the room |
| Nursery | 40–50% | Small airways; steadiness matters more than the exact figure |
| Attic | Tracks outdoors | A vented attic should be close to outdoor conditions |
By climate
A national average target is a compromise between climates that need opposite things. Chasing 40% in Florida costs a fortune; holding 50% in Minneapolis in January puts water on your windows.
| Climate | Target | Where |
|---|---|---|
| Hot and humid | 45–55% | Florida, Gulf Coast, Southeast |
| Hot and dry | 30–40% | Arizona, Nevada, New Mexico |
| Cold winters | 30–40%, sliding | Upper Midwest, Northeast, Mountain |
| Mild and damp | 40–50% | Pacific Northwest |
| Four seasons | 30–50%, seasonal | Mid-Atlantic, Ohio and Tennessee valleys |
For things rather than people
Materials care about stability more than the exact figure. Repeated large swings do more damage than a steady reading slightly outside the ideal.
| What | Range | Failure mode outside it |
|---|---|---|
| Hardwood floors | 35–55% | Gaps when dry, cupping when wet |
| Musical instruments | 40–50% | Cracked soundboards, shifting action |
| Books and paper | 35–50% | Brittle when dry, foxing and mold when damp |
| Artwork and photographs | 40–50% | Cockling, emulsion damage |
| Wine storage | 50–70% | Corks dry out below 50% |
| Tools and firearms | Below 50% | Rust accelerates above about 60% |
| Electronics in storage | Below 60% | Corrosion on contacts and boards |
Common questions
What is the ideal indoor humidity chart?
There are four that matter, and they are all on this page: the overall 30–50% band, the winter table where the target falls with the outdoor temperature, the room-by-room targets, and the climate targets.
Should indoor humidity be different in summer and winter?
Yes. 45–50% is comfortable in summer; in winter the ceiling is set by how cold your windows get, which means 40% in mild weather down to 25% in a hard freeze.
What humidity is best for hardwood floors and instruments?
35–55% for floors and 40–50% for instruments, with stability mattering more than the exact number. Repeated swings cause more damage than a steady reading slightly outside the range.
Is 60% humidity too high indoors?
It is the upper limit rather than a disaster. Dust mites thrive there and cold surfaces start to condense, so treat 60% as the point to act rather than the point where damage begins.
Sources
- US EPA — Mold and moisture guidance — the 30–50% range and the 10 sq ft remediation threshold
- ASHRAE Standard 55 — Thermal environmental conditions for human occupancy — indoor comfort and humidity limits
- US DOE 10 CFR 430 — Dehumidifier test procedure — the 2019 move to 65 °F rating conditions