Vapor Pressure Deficit (VPD) Calculator

Calculate accurate Vapor Pressure Deficit (VPD) to optimize transpiration, nutrient uptake, and humidity control for your indoor grow room or greenhouse.

Air Temperature Please enter a valid temperature

Temperature Unit

Relative Humidity (RH) %

Please enter a valid humidity between 0 and 100

Leaf Temp Offset (vs. Air) °F

LEDs: Leaves run ~2°F cooler (-2) | HPS: Leaves run ~2°F warmer (+2) Please enter a valid offset

Target Growth Stage

Calculation Results

Leaf VPD

— kPa

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How to use this VPD calculator

Enter your climate readings

Input the air temperature and relative humidity measured directly at canopy height. Readings taken at the floor or ceiling will skew your results.

Set the leaf temperature offset

Because plants transpire (sweat), leaves are usually cooler than the surrounding air. Under LED lights, leaves run about 1°C to 2°C (2°F to 4°F) cooler. Under hot HPS lights, leaves may run warmer than the air. Use an infrared (IR) thermometer on a mature fan leaf for exact numbers.

Select your growth stage

Choose whether your plants are in Propagation (clones/seedlings), Vegetative growth, or the Flowering phase. The calculator will adapt the target bands accordingly.

Review your target status

The tool outputs your True Leaf VPD in kilopascals (kPa). It instantly tells you if you are in the "sweet spot" or at risk of mold, nutrient lockout, or leaf burn.

Air Vapor Pressure Deficit (VPD) Chart for Greenhouses

Air Temp (°C)	Air Temp (°F)	Relative Humidity	Air VPD (kPa)
15 °C	59 °F	40%	1.02 kPa
15 °C	59 °F	50%	0.85 kPa
15 °C	59 °F	60%	0.68 kPa
15 °C	59 °F	70%	0.51 kPa
15 °C	59 °F	80%	0.34 kPa
15 °C	59 °F	90%	0.17 kPa
20 °C	68 °F	40%	1.40 kPa
20 °C	68 °F	50%	1.17 kPa
20 °C	68 °F	60%	0.94 kPa
20 °C	68 °F	70%	0.70 kPa
20 °C	68 °F	80%	0.47 kPa
20 °C	68 °F	90%	0.23 kPa
25 °C	77 °F	40%	1.90 kPa
25 °C	77 °F	50%	1.58 kPa
25 °C	77 °F	60%	1.27 kPa
25 °C	77 °F	70%	0.95 kPa
25 °C	77 °F	80%	0.63 kPa
25 °C	77 °F	90%	0.32 kPa
30 °C	86 °F	40%	2.55 kPa
30 °C	86 °F	50%	2.12 kPa
30 °C	86 °F	60%	1.70 kPa
30 °C	86 °F	70%	1.27 kPa
30 °C	86 °F	80%	0.85 kPa
30 °C	86 °F	90%	0.42 kPa

Frequently asked questions

What is Vapor Pressure Deficit (VPD)?

Vapor Pressure Deficit (VPD) is the difference between the amount of moisture the air can hold when fully saturated and the amount it currently holds. It represents the "drying power" of the air. It dictates how quickly water and nutrients are pulled through the plant's roots and out of its stomata (transpiration).

What is the difference between Air VPD and Leaf VPD?

Air VPD relies strictly on the air temperature. Leaf VPD incorporates the actual surface temperature of the plant's leaves. Because leaves cool themselves through transpiration, they often run cooler than the air around them. True Leaf VPD is the only metric the plant actually "feels."

What are the ideal VPD target ranges?

Propagation (Clones/Seedlings): 0.4 – 0.8 kPa. Undeveloped roots need a low deficit to prevent the plant from drying out.
Vegetative Growth: 0.8 – 1.2 kPa. The sweet spot for fast nutrient uptake, robust stem growth, and healthy transpiration without stress.
Flowering / Fruiting: 1.2 – 1.6 kPa. Drier conditions force stomata slightly closed, increasing plant resilience and critically reducing the risk of Botrytis (bud rot/mold) in dense flower clusters.

What happens if my VPD is too high or too low?

If VPD is too low (< 0.4 kPa), the air is nearly saturated. Plants cannot transpire, nutrient uptake stops (often leading to calcium deficiencies), and condensation can form on leaves, causing mold. If VPD is too high (> 1.6 kPa), the air is too dry. The plant loses water too rapidly, forcing the stomata to snap shut to survive, which halts photosynthesis and can cause crispy leaf edges (tip burn).

About this calculator

This VPD calculator provides commercial cultivators, greenhouse operators, and indoor hobbyists with precise environmental targets using the industry-standard Tetens equation for saturation vapor pressure.

The core mathematical framework driving these calculations involves finding the saturation vapor pressure (SVP) of both the air and the leaf, and comparing it to the actual vapor pressure (AVP):

SVP = 0.61078 × exp[ (17.27 × T_Celsius) ÷ (T_Celsius + 237.3) ]
AVP = SVP_Air × (Relative Humidity ÷ 100)

Air VPD = SVP_Air - AVP
Leaf VPD = SVP_Leaf - AVP

Why LED lighting changed the game: Older VPD charts were built entirely around HPS (High Pressure Sodium) lights, which dump massive amounts of infrared radiant heat directly onto the plant canopy, making leaves significantly warmer than the air. Modern LED grow lights lack this radiant heat penalty. Consequently, leaves grown under LEDs run cooler, meaning you must maintain higher room temperatures to hit the same ideal Leaf VPD targets.