VPD calculator
Vapor pressure deficit is the drying power of the air — the number indoor growers tune instead of humidity. Enter temperature and RH for the VPD in kPa and whether it sits in the healthy range.
Evidence-checked. Facts and figures on this page are verified against published standards and government sources (Tetens saturation-vapour-pressure equation). Last verified July 2026 — our methodology.
Vapor pressure deficit
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- Zone
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- Saturation pressure
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- Suits best
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VPD is the gap between how much moisture the air could hold at this temperature (saturation pressure, from the Tetens equation) and how much it actually holds (saturation × RH). A bigger deficit pulls water out of leaves faster. This uses air temperature; because leaves run a degree or two cooler, true leaf VPD is usually a touch lower.
What VPD tells growers
Low VPD (humid, muggy air) slows transpiration and invites mold and mildew; high VPD (hot, dry air) stresses plants and can wilt them. Common targets are roughly 0.4–0.8 kPa for seedlings and clones, 0.8–1.2 kPa in vegetative growth, and 1.2–1.6 kPa in flower. Because VPD couples temperature and humidity, you steer it with the same tools this site covers — a right-sized dehumidifierto raise VPD, or a humidifier to lower it. To see the moisture side in other units, use theabsolute humidity calculator, or check the plain dew point with thedew point calculator.