Dew Point Chart.
The full dew point chart: read the dew point for any air temperature and relative humidity, then watch a cold pane fog and bead with condensation as the air nears saturation. Color-coded from comfortable to mold-prone, printable in °F or °C.
Interactive dew point chart
Tap any cell to read its dew point and watch the pane react. As the dew point closes on the surface temperature, the glass fogs and dew beads up, exactly how condensation and mold begin in a real grow room. Prefer a single readout with a live plant? Use the VPD calculator, or scan every combination on the VPD chart.
How to read a dew point chart
A dew point chart turns two readings, air temperature and relative humidity, into the dew point: the temperature at which that air can hold no more water and starts condensing on any cooler surface. It is the single number that predicts fogged glass, damp walls, and grow-room mold before you can see them.
Step by step
- 1Find your air temperature along the top axis.
- 2Find your relative humidity down the side axis.
- 3The cell where they cross is the dew point, and its color is the comfort and mold-risk zone.
- 4Subtract that dew point from your coldest surface. A spread under about 4°F means condensation and mold are likely.
Dew point chart vs humidity chart
A relative humidity chart shows a percentage that shifts with temperature, so the same 60% reading means very different things at 60°F and 90°F. A dew point chart shows the real moisture as a temperature, which is why it beats a humidity chart for predicting condensation, comfort, and mold. In effect it is a simplified psychrometric chart, and the math is the Magnus equation, the same saturation-vapor-pressure formula behind vapor pressure deficit (VPD). Below freezing, the reading becomes the frost point and moisture deposits as frost.
Dew point chart key facts
- What it shows: the dew point, the temperature where air condenses on a surface, for every combination of temperature and relative humidity.
- Formula (Magnus): Td = (237.3 × γ) ÷ (17.27 − γ), where γ = ln(RH/100) + (17.27 × T)/(237.3 + T), T in °C.
- Mold zone: cells above a 60°F dew point are mold-prone in a grow room; below is mold-safe.
- Spread rule: if your coldest surface sits within about 4°F of the dew point, expect condensation.
- Comfort: below 55°F dry and pleasant, 60–65°F sticky, above 70°F oppressive.
- Related: pairs with the VPD chart, which reads the same air for plant transpiration instead of condensation.
Dew point comfort and mold-risk chart
Comfort and mold both track the dew point, not relative humidity. Here is what each band on the chart means indoors and in a grow tent.
| Dew point | How it feels | Grow-room note |
|---|---|---|
| Below 50°F | Dry, crisp | Very mold-safe; may be dry for clones |
| 50–55°F | Pleasant | Comfortable working range |
| 55–60°F | Slightly humid | Watch cool surfaces at lights-off |
| 60–65°F | Sticky | Elevated mold risk; add dehumidification |
| 65–70°F | Muggy | High mold risk; condensation likely |
| Above 70°F | Oppressive | Severe; expect condensation and mildew |
Dew point chart questions
How do you read a dew point chart?
Find your air temperature along the top and relative humidity down the side. The cell where they meet is the dew point, the temperature at which the air condenses. Its color is the comfort and mold-risk zone, green for dry and safe through red for wet and mold-prone.
What is a comfortable dew point on the chart?
Below 55°F feels dry and comfortable, 55 to 60 is pleasant, 60 to 65 turns sticky, and above 65 is muggy. In a grow room, keeping the dew point below about 60°F keeps surfaces mold-safe.
What dew point means mold risk?
A dew point above about 60°F, or any cell within roughly 4°F of your coldest surface, is the condensation and mold zone. Leaves and walls run coldest at lights-off, so treat those cells as high risk.
What is the difference between a dew point chart and a humidity chart?
A humidity chart shows relative humidity, a percentage that changes with temperature. A dew point chart shows the actual moisture as a temperature, so it directly predicts condensation and comfort. Same humidity, different temperatures, very different dew points.
Is the dew point chart in Fahrenheit or Celsius?
Both. Use the °F and °C toggle in the header and the whole chart, values and axes, converts instantly.
How is the dew point chart related to VPD?
Both come from temperature and relative humidity. A VPD chart shows the drying power on the plant; a dew point chart shows where that same air condenses on a surface. Read VPD for transpiration and the dew point for condensation and mold.
What is the frost point on a dew point chart?
Any cell where the dew point falls below freezing, 32°F or 0°C, is technically a frost point: moisture deposits on surfaces as frost instead of liquid dew. That is why cold glazing and tent walls frost over on winter nights even without rain or visible moisture.