Air VPD vs leaf VPD
Air-based VPD assumes the leaf is at air temperature. Leaf-based VPD uses leaf temperature and better represents the vapor-pressure difference at the leaf surface when a reliable leaf-temperature measurement is available.
Quick mode
Leaf-VPD calculator
Start with the measurements you actually have. Measured leaf temperature is preferred; offset mode is an estimate.
Example: −1 °C means the leaf is estimated 1 °C cooler than room air.
Use a representative canopy measurement, not one unusually hot or cold leaf.
These are broad operating examples, not crop-stage prescriptions. Your measured conditions and saved target low/high values remain the source of truth.
<0.8Low demand
0.8–1.2Moderate
1.2–1.6Higher
>1.6Very high
Broad teaching bands only. Cultivar, root water supply, light, airflow, CO₂, leaf temperature, canopy density, and acclimation all affect plant response.
Interactive map
Nearby condition heatmap
The map recalculates around your current reading. Offset and same-as-air modes keep that relationship as air temperature changes; measured-leaf mode holds the entered leaf measurement fixed for comparison.
Swipe horizontally to explore the full temperature × RH map. Row labels stay pinned.
DEW marks conditions where the calculated leaf surface is at or below the surrounding-air dew boundary; interpret those cells as condensation risk, not ordinary low VPD.
Environmental profile
Save a repeatable room or canopy-zone profile. The target band is used for logger analysis; it is a user-defined operating range, not a universal biological prescription.
Profiles stay in this browser. Logger analysis uses the current target band and sustain settings.
Logger CSV trend analysis
Import environmental logger data to calculate leaf VPD for every row. Accepted headers are flexible: timestamp/time/date, temperature/temp/air_temp, humidity/rh, and optionally leaf_temp or leaf_offset. This tool processes the file locally in your browser.
No logger data loaded.
Average VPD—
Minimum—
Maximum—
Rows analyzed—
Inside target band—
Sustained excursions—
Dew-boundary rows—
| Time | Air temp | RH | Leaf temp | Leaf VPD | Dew risk |
|---|
Trend interpretation matters more than a single peak. Correlate excursions with lights, irrigation, HVAC/dehumidification cycles, canopy temperature, and sensor placement before changing setpoints.
Sensor placement matters
- Keep temperature and RH measurements from the same representative zone.
- Record sensor height and location.
- Check canopy interiors and edges instead of relying on one exposed sensor.
Transitions matter
Lights-off, irrigation, HVAC cycling, dehumidification, door openings, and changing radiation can produce short-lived conditions that daily averages hide. Trend data is often more useful than a single screenshot.
Related plant references
Use Plant Atlas for plant anatomy and Terpene Atlas for chemistry context. These references support interpretation but do not replace environmental measurement.
Measurement-first interpretation
What this result actually means
Air measurementLeaf measurementDew / condensation boundary
Leaf VPD
Leaf VPD compares saturation vapor pressure at the leaf surface with the actual vapor pressure of the surrounding air. When leaf temperature differs from room temperature, leaf VPD can differ materially from air-only VPD.
Dew point
Dew point is the temperature where the current air mass reaches saturation. A leaf or surface approaching dew point has greater condensation risk even when room RH remains below 100%.
Target bands
The selected band is an operating reference, not a universal biological law. Genetics, root-zone water supply, PPFD, CO₂, airflow, acclimation, canopy density, and sensor placement can change plant response.
Use the scenario solver as a mathematical comparison. It shows how temperature or RH would change the calculation while holding other assumptions constant; it does not by itself prescribe a climate-control action.