VPD Calculator

VPD (Vapor Pressure Deficit) is one of the most important climate parameters in indoor growing. It describes the difference between the actual and maximum possible water vapor content of the air and determines how efficiently your plants transpire. Our free VPD calculator computes the value instantly and displays it on an interactive chart.

Unlike humidity alone, VPD also accounts for temperature. A humidity of 60% may be optimal at 20°C but already too dry at 30°C. VPD gives you the true value your plants experience – that's why professional growers rely on VPD control rather than simple hygrometer readings.

For seedlings and clones, we recommend a VPD of 0.4–0.8 kPa (high humidity, moderate temperature). During the vegetative phase, the optimum is 0.8–1.2 kPa. During flowering, experienced growers can increase VPD to 1.0–1.5 kPa to maximize transpiration and nutrient uptake.

Important: Leaf temperature is typically 1–3°C lower than air temperature. Our calculator accounts for this difference with the leaf offset field. For LED grow rooms, an offset of 2°C is typical. With HPS lamps, it may be lower since infrared radiation warms the leaves more.