What is VPD in cannabis curing?
Vapor Pressure Deficit (VPD), measured in kilopascals (kPa), is the difference between the saturation vapor pressure of air at a given temperature and the actual vapor pressure of that air. Lower VPD slows moisture migration out of the flower; higher VPD accelerates it. Most commercial cannabis cure rooms operate between 0.7 and 1.1 kPa, with the exact target driven by room temperature and target relative humidity.
VPD reference for cannabis curing
The table below shows VPD across common cure room conditions. Stay within the 0.7–1.1 kPa range; use the lower end (0.70–0.80 kPa) for gentler, terpene-protective cures and the upper end (0.95–1.10 kPa) when you need more aggressive moisture pull-down on incoming high-moisture flower.
| Room temperature | Relative humidity | Resulting VPD |
|---|---|---|
| 60°F | 60% RH | 0.70 kPa |
| 60°F | 57% RH | 0.76 kPa |
| 60°F | 55% RH | 0.79 kPa |
| 60°F | 50% RH | 0.88 kPa |
| 62°F | 50% RH | 0.94 kPa |
| 65°F | 50% RH | 1.05 kPa |
The standard Cure Puck setpoint is 60°F at roughly 57% RH, putting the room around 0.76 kPa — in the middle of the cure band. These conditions target a finished water activity (aw) of 0.56–0.60, the proven range for shelf stability, terpene retention, and smoke quality. Pull aw above 0.63 and mold risk climbs; below 0.55 and you've over-dried.
How to use this VPD calculator
- Select your target cured flower RH % (this will determine your finished water activity)
- Select the verified maximum temperature in the cure room.
- Select the verified minimum temperature in the cure room.
- Calculator returns VPD in kPa
Note: Measure the high and low temps of the cure room over a 24 hour period to determine this range. Using a cure puck, monitored through the app is the most effective method.
VPD vs. water activity (aw): which should you trust?
VPD describes the air pulling moisture from the flower. Water activity describes the flower itself. VPD is what you control via HVAC and dehumidification; aw is what determines whether your product is shelf-stable, moldy, or harsh. The two work together: a 0.76 kPa cure room (60°F at 57% RH) will, over time, drive flower toward roughly 0.58 aw. The Cure Puck system measures aw directly across multiple sample points in real time, rather than inferring flower moisture from room conditions alone.
Frequently asked questions
What is the ideal VPD for curing cannabis?
Cannabis cure rooms typically run between 0.7 and 1.1 kPa, depending on target RH and room temperature. Use the lower end (0.70–0.80 kPa) for gentler, terpene-protective cures, and the upper end (0.95–1.10 kPa) when you need more aggressive moisture pull-down on incoming high-moisture flower.
Why does my cure room VPD stay constant but my flower keeps drying?
Because the flower keeps releasing moisture into the air, and your dehumidifier keeps removing it. VPD measures air deficit, not flower moisture. That's why direct aw monitoring is more reliable for knowing when to seal.
What temperature should my cure room be?
60°F (15.5°C) is the standard target. Lower preserves terpenes and slows the cure; higher accelerates the cure but increases volatile loss.
Does cure-room VPD include leaf temperature like cultivation VPD?
No. There's no actively transpiring plant in the cure room, so VPD here is air-only — saturation vs. actual vapor pressure at room temperature. Cultivation VPD calculators that ask for leaf temperature use a different model and will give different numbers.
Want to go deeper?
For the full curing methodology — water activity targets, room setup, sampling cadence, and the science behind each step — download The Ultimate Nerd's Guide to Curing Cannabis or read the Cure Puck SOP.