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VPD Chart

This VPD chart for cannabis shows leaf VPD at every temperature and humidity, coloured for your growth stage. Print it or save it as a PDF for the grow room wall.

Leaf VPD chart (°C)Vegetative · ideal 0.80–1.20 kPa · leaf 2 °C (3.6 °F) cooler than the airvpdcalculator.com

Too low
Slightly low
Ideal
Slightly high
Too high

Air ↓ RH →	30%	35%	40%	45%	50%	55%	60%	65%	70%	75%	80%	85%	90%	95%
16°C 61°F	1.05	0.96	0.87	0.78	0.69	0.60	0.51	0.42	0.33	0.23	0.14	0.05	−0.04	−0.13
17°C 63°F	1.12	1.03	0.93	0.83	0.74	0.64	0.54	0.45	0.35	0.25	0.16	0.06	−0.04	−0.14
18°C 64°F	1.20	1.10	0.99	0.89	0.79	0.68	0.58	0.48	0.37	0.27	0.17	0.06	−0.04	−0.14
19°C 66°F	1.28	1.17	1.06	0.95	0.84	0.73	0.62	0.51	0.40	0.29	0.18	0.07	−0.04	−0.15
20°C 68°F	1.36	1.25	1.13	1.01	0.89	0.78	0.66	0.54	0.43	0.31	0.19	0.08	−0.04	−0.16
21°C 70°F	1.45	1.33	1.20	1.08	0.95	0.83	0.71	0.58	0.46	0.33	0.21	0.08	−0.04	−0.17
22°C 72°F	1.55	1.41	1.28	1.15	1.02	0.88	0.75	0.62	0.49	0.36	0.22	0.09	−0.04	−0.17
23°C 73°F	1.64	1.50	1.36	1.22	1.08	0.94	0.80	0.66	0.52	0.38	0.24	0.10	−0.04	−0.18
24°C 75°F	1.75	1.60	1.45	1.30	1.15	1.00	0.85	0.70	0.56	0.41	0.26	0.11	−0.04	−0.19
25°C 77°F	1.86	1.70	1.54	1.38	1.23	1.07	0.91	0.75	0.59	0.43	0.28	0.12	−0.04	−0.20
26°C 79°F	1.98	1.81	1.64	1.47	1.30	1.14	0.97	0.80	0.63	0.46	0.29	0.13	−0.04	−0.21
27°C 81°F	2.10	1.92	1.74	1.56	1.39	1.21	1.03	0.85	0.67	0.49	0.32	0.14	−0.04	−0.22
28°C 82°F	2.23	2.04	1.85	1.66	1.47	1.28	1.09	0.90	0.72	0.53	0.34	0.15	−0.04	−0.23
29°C 84°F	2.36	2.16	1.96	1.76	1.56	1.36	1.16	0.96	0.76	0.56	0.36	0.16	−0.04	−0.24
30°C 86°F	2.51	2.29	2.08	1.87	1.66	1.45	1.23	1.02	0.81	0.60	0.39	0.17	−0.04	−0.25
31°C 88°F	2.66	2.43	2.21	1.98	1.76	1.53	1.31	1.09	0.86	0.64	0.41	0.19	−0.04	−0.26
32°C 90°F	2.82	2.58	2.34	2.10	1.87	1.63	1.39	1.15	0.91	0.68	0.44	0.20	−0.04	−0.27
33°C 91°F	2.98	2.73	2.48	2.23	1.98	1.73	1.47	1.22	0.97	0.72	0.47	0.22	−0.03	−0.29
34°C 93°F	3.16	2.89	2.63	2.36	2.10	1.83	1.56	1.30	1.03	0.77	0.50	0.23	−0.03	−0.30

Leaf VPD chart (°F)Vegetative · ideal 0.80–1.20 kPa · leaf 2 °C (3.6 °F) cooler than the airvpdcalculator.com

Too low
Slightly low
Ideal
Slightly high
Too high

Air ↓ RH →	30%	35%	40%	45%	50%	55%	60%	65%	70%	75%	80%	85%	90%	95%
60°F 16°C	1.02	0.93	0.85	0.76	0.67	0.58	0.49	0.40	0.32	0.23	0.14	0.05	−0.04	−0.13
62°F 17°C	1.10	1.01	0.91	0.82	0.72	0.63	0.53	0.44	0.34	0.25	0.15	0.06	−0.04	−0.13
64°F 18°C	1.18	1.08	0.98	0.88	0.77	0.67	0.57	0.47	0.37	0.27	0.16	0.06	−0.04	−0.14
66°F 19°C	1.27	1.16	1.05	0.94	0.83	0.72	0.61	0.51	0.40	0.29	0.18	0.07	−0.04	−0.15
68°F 20°C	1.36	1.25	1.13	1.01	0.89	0.78	0.66	0.54	0.43	0.31	0.19	0.08	−0.04	−0.16
70°F 21°C	1.46	1.34	1.21	1.09	0.96	0.84	0.71	0.59	0.46	0.33	0.21	0.08	−0.04	−0.17
72°F 22°C	1.57	1.43	1.30	1.16	1.03	0.90	0.76	0.63	0.49	0.36	0.23	0.09	−0.04	−0.18
74°F 23°C	1.68	1.54	1.39	1.25	1.11	0.96	0.82	0.68	0.53	0.39	0.25	0.10	−0.04	−0.18
76°F 24°C	1.80	1.64	1.49	1.34	1.18	1.03	0.88	0.72	0.57	0.42	0.26	0.11	−0.04	−0.19
78°F 26°C	1.92	1.76	1.60	1.43	1.27	1.10	0.94	0.78	0.61	0.45	0.29	0.12	−0.04	−0.21
80°F 27°C	2.06	1.88	1.71	1.53	1.36	1.18	1.01	0.83	0.66	0.48	0.31	0.13	−0.04	−0.22
82°F 28°C	2.20	2.01	1.82	1.64	1.45	1.27	1.08	0.89	0.71	0.52	0.33	0.15	−0.04	−0.23
84°F 29°C	2.35	2.15	1.95	1.75	1.55	1.35	1.15	0.96	0.76	0.56	0.36	0.16	−0.04	−0.24
86°F 30°C	2.51	2.29	2.08	1.87	1.66	1.45	1.23	1.02	0.81	0.60	0.39	0.17	−0.04	−0.25
88°F 31°C	2.68	2.45	2.22	2.00	1.77	1.54	1.32	1.09	0.87	0.64	0.41	0.19	−0.04	−0.26
90°F 32°C	2.85	2.61	2.37	2.13	1.89	1.65	1.41	1.17	0.93	0.69	0.45	0.20	−0.04	−0.28
92°F 33°C	3.04	2.78	2.53	2.27	2.02	1.76	1.50	1.25	0.99	0.73	0.48	0.22	−0.03	−0.29
94°F 34°C	3.24	2.97	2.69	2.42	2.15	1.88	1.60	1.33	1.06	0.79	0.51	0.24	−0.03	−0.30

Using the chart

Each cell is leaf VPD: the vapour pressure inside the leaf (saturated at leaf temperature) minus the vapour pressure of the air. The leaf temperature comes from the air temperature and how much cooler or warmer you set the leaf, so a leaf 2 °C cooler than 26 °C air is 24 °C.

Want one exact number instead? Use the VPD calculator, which shows your point on a live version of this chart and tells you what to change.

VPD chart for autoflowers

Autoflowers move from one stage to the next by age, not by day length, so pick the chart by week. A typical autoflower takes about 10 weeks from seed to harvest; some take up to 14, so go by what you see in the plant.

Which stage chart to use for an autoflower, by week
Week from seed	What the plant is doing	Use the chart for
1–2	Seedling	Clones / Seedlings
3–4	Fast leaf growth	Vegetative
5–7	Pre-flower, then first buds	Early Flower
8 to harvest	Buds fill out and ripen	Late Flower

Most growers give autoflowers 18 hours of light a day for their whole life (some use 20). Splitting flower into early and late is our choice.

VPD chart for drying

Drying is slow on purpose: a low VPD pulls water out of the buds gently. The classic 60/60 method is 60 °F (15.6 °C) at 60% relative humidity for 10 to 21 days, about 0.71 kPa. Oregon State University’s slow drying for hemp runs warmer and drier, 18–21 °C at 50–55% RH (0.93–1.24 kPa), then cures at 18 °C and 60%.

Buds hang at room temperature, so this table is air VPD with no leaf offset. The 60/60 cell is outlined.

Air VPD in kPa for a drying room, by temperature and relative humidity
Air ↓ RH →	45%	50%	55%	60%	65%	70%
58°F 14°C	0.90	0.82	0.74	0.66	0.58	0.49
60°F 16°C	0.97	0.88	0.80	0.71	0.62	0.53
62°F 17°C	1.04	0.95	0.85	0.76	0.66	0.57
64°F 18°C	1.12	1.02	0.92	0.81	0.71	0.61
66°F 19°C	1.20	1.09	0.98	0.87	0.76	0.65
68°F 20°C	1.29	1.17	1.05	0.94	0.82	0.70
70°F 21°C	1.38	1.25	1.13	1.00	0.88	0.75

Sizing a dehumidifier for the drying room? The dehumidifier size calculator has a drying-room mode.

Reading a cannabis VPD chart

A VPD chart for weed (cannabis) does the sums for you. Each row is an air temperature, 16–34 °C on the Celsius sheet or 60–94 °F on the Fahrenheit sheet, and each column is a relative humidity from 30% to 95%. The cell where they meet is leaf VPD, with the leaf set cooler than the air by the offset you choose.

A worked example: on the Celsius sheet, find the 26 °C row and the 60% column. With the leaf 2 °C cooler (the LED setting), the cell reads 0.97 kPa. On the Fahrenheit sheet, the 78 °F row at 60% reads 0.94 kPa with the leaf 3.6 °F cooler. Both are green on the veg chart.

Green is the ideal band for the stage you picked; blue is too low, orange and red too high. The legend above each sheet gives the exact range for each colour. Within 0.2 kPa of the band counts as slightly low or high, so a cell next to the green is a nudge, not an alarm. If you have used any of the calculators on this site, your last reading is outlined on the chart, so you can find your own cell straight away.

VPD chart for veg

The veg chart is green from 0.80 to 1.20 kPa. Steady transpiration in this stage drives nutrient uptake and fast leaf growth. At 26 °C with LED lights, the 55% and 60% columns are green; 50% reads 1.30 kPa, slightly high.

To act on it, find your cell and move towards green. Moving right, to a higher humidity, lowers VPD. Moving up the table, to a cooler row, also lowers it. Choose whichever is easier to change in your room, change it a little, and read again once the room has settled.

VPD chart for flower

Photoperiod plants start flowering when they get about 12 hours of dark, and the chart has two flower stages: early flower at 1.00–1.50 kPa and late flower at 1.20–1.50 kPa. The drier air in late flower helps keep dense buds free of mould. None of the published cannabis ranges goes above 1.5 kPa, so neither does the chart.

At 26 °C (78.8 °F) with LED lights, 50% RH gives about 1.30 kPa, ideal for both flower stages. If you run added CO₂ at about 1,200 ppm or more, aim for the upper half of the band, for example 1.25–1.50 kPa in early flower. The VPD calculator has a switch that does this for you.

Mistakes the chart cannot catch

The wrong leaf offset. The LED setting is 2 °C (3.6 °F) cooler than the air. Under HPS leaves run warmer, about 0.7 °C (1.3 °F) cooler than the air. At 26 °C and 60% that moves the cell from 0.97 to 1.21 kPa. If you can measure your leaves, the leaf VPD calculator turns the reading into an offset.
Mixing units. The offset is a difference, so 2 °C cooler is 3.6 °F cooler, not 35.6 °F.
A hygrometer that reads 5% out. At 26 °C that shifts VPD by about 0.17 kPa, nearly half a band, or about one column on the chart.
Only checking with the lights on. The chart shows daytime conditions. When the room cools at night, humidity rises and leaves can reach the dew point. Check that with the dew point chart.
Printing the wrong stage. Choose All 4 stages to print one sheet per stage, and swap the sheet on the wall as the plants move on.

FAQ

About the VPD chart

What is a good VPD range?

For cannabis, about 0.5–1.0 kPa for clones and seedlings, 0.8–1.2 kPa in veg, 1.0–1.5 kPa in early flower and 1.2–1.5 kPa in late flower. These are leaf VPD starting points drawn from published ranges and grower guides, not fixed rules, so watch how your plants respond and adjust.

Is 1.8 VPD too high?

Yes. 1.8 kPa is above every stage on this chart; the highest target, late flower, stops at 1.5 kPa, so 1.8 shows as too high. At that point the air pulls water from the leaves faster than the roots can replace it. Raise the humidity or lower the temperature.

Is 1.5 VPD too high?

Not in flower: 1.5 kPa is the top of both the early and late flower bands, so it still reads as ideal there. In veg, where the band stops at 1.2 kPa, and for seedlings, which stop at 1.0 kPa, it is too high. None of our sources goes above 1.5 kPa.

What VPD for seedlings and clones?

Aim for a leaf VPD of 0.5–1.0 kPa. Roots are small, so keep transpiration gentle and humidity high. At 24 °C (75.2 °F) with the leaf 2 °C cooler, 70% RH gives about 0.56 kPa, inside the band, while 75% RH drops it to 0.41 kPa, which is slightly low.

What VPD for late flower?

Aim for 1.2–1.5 kPa, the driest air of the cycle, which helps protect dense buds from bud rot. At 26 °C (78.8 °F) under LEDs, 50% RH gives about 1.30 kPa. Splitting flower into early and late is our own choice; the published flowering range is 1.0–1.5 kPa.

What VPD for autoflowers?

Use the same stage bands, chosen by week from seed: weeks 1–2 seedling (0.5–1.0 kPa), weeks 3–4 veg (0.8–1.2), weeks 5–7 early flower (1.0–1.5) and week 8 onward late flower (1.2–1.5). Autoflowers flower by age, not day length, and most get 18 hours of light a day.

What VPD for drying?

About 0.7 kPa of air VPD. The common 60/60 method, 60 °F (15.6 °C) at 60% RH for 10 to 21 days, works out at 0.71 kPa. Oregon State's slow drying for hemp, 18–21 °C at 50–55% RH, runs about 0.93–1.24 kPa. Buds hang at room temperature, so use air VPD.

How do I read a VPD chart?

Find your air temperature in the left column and your relative humidity across the top. The cell where they meet is your leaf VPD. Green cells are in the ideal range for the stage you picked.

Sources

The formulas and target ranges on this page come from these references.

Allen, Pereira, Raes & Smith (1998). Crop evapotranspiration, FAO Irrigation and Drainage Paper 56, chapter 3, equations 11 and 19. www.fao.org/4/x0490e/x0490e07.htm
Corredor-Perilla, Kwon & Park (2025). Elevated relative humidity significantly decreases cannabinoid concentrations while delaying flowering development in Cannabis. Frontiers in Plant Science (leaf VPD equation 3, and the cannabis VPD ranges it reports from earlier work). doi.org/10.3389/fpls.2025.1678142
Pulse Grow (2020): VPD guide for cannabis growers. pulsegrow.com/blogs/learn/vpd
Nelson & Bugbee (2015). Analysis of environmental effects on leaf temperature under sunlight, HPS, metal halide and LED. PLoS ONE 10(10), e0138930. doi.org/10.1371/journal.pone.0138930
Bergman, R. (updated 2026). Autoflower life cycle. ILGM: seedling weeks 1–2, vegetative 3–4, pre-flower 5, flowering 6–10; about 10 weeks seed to harvest; 18 hours of light (20/4 also used). ilovegrowingmarijuana.com/growing/autoflower-life-cycle
Kinneman, K. (2024). Navigating the modern and antiquated ideas about drying. mg Magazine: the “60/60” method dries at 60 °F and 60% relative humidity for 10 to 21 days. mgmagazine.com/business/growing-horticulture/navigating-the-modern-and-antiquated-ideas-about-drying
Oregon State University Extension (2022). Post-harvest processing of hemp flowers: slow drying at 18–21 °C and 50–55% RH; curing at 18 °C and 60% RH for 14 days. extension.oregonstate.edu/catalog/post-harvest-processing-hemp-flowers

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