How to use the checker
- Choose Celsius or Fahrenheit before entering values.
- Enter air temperature, relative humidity, surface temperature, and planned time.
- Review the dew point, temperature gap, and the OK / Caution / Hold decision.
- Copy the share link to pass the same inputs to someone else.
Calculation formulas
- γ = ln(RH / 100) + (a × T) / (b + T)
- Td = (b × γ) / (a − γ)
- Gap = surface temperature − dew point
Notes
- This checker is a practical field aid, not a substitute for product data sheets, site specifications, or supervisor instructions.
- Weather can change quickly. Recheck surface temperature when sun, wind, or cloud cover changes.
- Calculations stay in the browser. No input is sent to the server.
Frequently asked questions
Why is the threshold 3°C / 5°F?
It gives a practical buffer above the dew point and is easy to remember on site.
Why is planned time not part of the calculation?
The decision is based on measured temperature and humidity. Planned time is recorded only as a reminder.
Can I work in Fahrenheit?
Yes. Switch the unit system; the tool preserves the same physical temperatures when units change.
What does Caution mean?
The surface is above the dew point, but the margin is too small for a comfortable painting window.
What happens at 100% humidity?
The dew point reaches the air temperature, so the surface must be clearly warmer to reduce condensation risk.