Should I open my windows?
To dry out a room, outdoor air has to be drier than indoor air — and relative humidity alone can fool you. Enter both temperatures and humidities to compare the real moisture and get a straight answer.
Evidence-checked. Facts and figures on this page are verified against published standards and government sources (Absolute humidity comparison (Magnus formula)). Last verified July 2026 — our methodology.
Verdict
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- Indoor moisture
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- Outdoor moisture
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- Difference
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The comparison uses absolute humidity — the actual grams of water in each cubic metre of air — not relative humidity, because warm and cool air at the "same" RH can carry very different amounts of water. If the outdoor air holds meaningfully less water, opening up lets the drier air swap in. If it holds more, you would be importing moisture.
Why relative humidity misleads here
A cool 70% morning outside can actually be drier than your 60% living room, because cool air holds less water to begin with — so opening the windows would help even though the outdoor number looks higher. This tool cuts through that by comparing true moisture content. When the answer is "keep them closed," aright-sized dehumidifieris the way to dry the room; the full trade-off is indehumidifier vs opening windows. To dig into the moisture numbers, see theabsolute humidity calculatorand dew point vs relative humidity.