Free download
Free VPD chart
Every VPD value from 18 to 32 °C and 40 to 85 % humidity on one A4 page – print it, tape it to your tent, done.
How to read it
Find your air temperature at the top and your relative humidity on the left. Where they meet is your VPD in kPa. The shade tells you the zone:
| Zone | VPD |
|---|---|
| Too wet | under 0.4 kPa |
| Clones & seedlings | 0.4–0.8 kPa |
| Veg | 0.8–1.2 kPa |
| Flower | 1.2–1.6 kPa |
| Too dry | over 1.6 kPa |
Air chart or leaf chart?
Most VPD charts – and the first PDF – show air VPD. Under LED grow lights the leaves run 1–3 °C cooler than the air, so what the plant really feels is a bit lower. The leaf VPD chart already subtracts 2 °C for the leaf: read it at your air temperature during lights-on. At night, use the air chart. Why leaf temperature matters.
Need an exact number?
The chart rounds to 1 °C and 5 % steps. For anything in between, use the VPD calculator – it also takes a custom leaf offset.
The math behind it
Saturation vapor pressure with the Magnus–Tetens formula, the same numbers as on the back of our shirts:
VPD = 0.6108 × e17.27·T / (T + 237.3) × (1 − RH/100)
Questions growers ask
What is a VPD chart?
A table of vapor pressure deficit values for every combination of air temperature and relative humidity, colored by zone – too wet, clone, veg, flower and too dry. Find your temperature and humidity and read your VPD.
Is this chart air VPD or leaf VPD?
The main chart shows air VPD, like most charts. The leaf chart already subtracts 2 °C for the leaf, which is typical under LED grow lights during lights-on.
Which chart should I use under LED lights?
During lights-on the leaf VPD chart is closer to what your plants feel. At night use the air VPD chart – without light the leaf is about as warm as the air.
Can I print and share the chart?
Yes. The PDFs are free to print and hang in your grow room. If you share them online, please link back to trichomesociety.com/vpd-chart.