Calculator Inputs
Formula Used
The Magnus method estimates saturation vapour pressure from air temperature. Relative humidity scales that pressure to the actual vapour pressure. The inverse equation returns the dew point temperature accurately.
γ = ln(RH / 100) + (a × T) / (b + T) Td = (b × γ) / (a - γ) RH = 100 × es(Td) / es(T)
Arden Buck uses refined empirical constants across normal weather ranges. Lawrence offers a fast approximation with reduced precision. Wet-bulb mode applies a pressure-adjusted psychrometric relationship for estimates.
How to Use
- Select the calculation mode matching your known values.
- Choose a formula and preferred temperature units.
- Enter pressure directly or calculate it from altitude.
- Add a surface temperature for condensation checking.
- Choose comparison, live preview, or batch processing options.
- Submit the form and review every calculated metric.
- Copy, export CSV, or save the results as PDF.
Example Data
| Air temperature | Relative humidity | Approximate dew point | Typical interpretation |
|---|---|---|---|
| 10°C | 50% | 0°C | Dry and cool |
| 20°C | 60% | 12°C | Comfortable |
| 25°C | 80% | 21°C | Humid |
| 32°C | 70% | 26°C | Oppressive |
Applications and Accuracy
Dew point supports HVAC sizing, weather analysis, storage, farming, and process control. Surface checks help identify condensation on windows, ducts, pipes, and walls. Always confirm critical designs using calibrated instruments and accepted standards.
Empirical formulas provide estimates rather than laboratory-grade psychrometric measurements. Accuracy declines with extreme temperatures, unusual pressure, or poor sensors. Wet-bulb estimates also depend strongly on airflow and ventilation.
The mould and fog indicators are general screening guides. They do not replace professional environmental or building assessments. Use local safety requirements for every regulated engineering decision.
Frequently Asked Questions
What is dew point?
Dew point is the temperature where air becomes saturated. Further cooling can produce condensation, dew, fog, or frost. Higher dew points usually feel more humid to people.
Which formula should I choose?
Magnus works well for most everyday calculations. Arden Buck is useful for refined weather estimates. Compare methods when precision matters across unusual conditions.
Can dew point exceed air temperature?
Normally, dew point cannot exceed the measured air temperature. Higher results often indicate inconsistent inputs or sensor errors. Saturated air has equal air and dew temperatures.
Why does altitude matter?
Altitude changes atmospheric pressure and psychrometric wet-bulb calculations. Standard dew point from temperature and humidity needs less correction. Pressure remains important for humidity ratio calculations.
What causes window condensation?
Condensation forms when glass cools below the indoor dew point. Better insulation keeps interior glass surfaces warmer. Ventilation or dehumidification can also reduce condensation risk.
What is vapour pressure deficit?
Vapour pressure deficit measures the atmosphere's remaining drying capacity. Growers use it to evaluate plant transpiration conditions. Very high values can increase moisture stress quickly.
What is absolute humidity?
Absolute humidity describes water vapour mass within air volume. This calculator reports grams of water per cubic metre. Temperature changes can affect that volume-based value significantly.
How does batch mode work?
Each line accepts temperature, humidity, and an optional unit. Valid units are C, F, and K. Results appear in a separate table after submission.
Can this calculator predict mould?
It provides a general moisture-related mould risk indicator. Real mould growth also depends on materials and duration. Professional inspection is necessary for suspected building contamination.
How should I save results?
Use copy for plain text sharing. Download CSV for spreadsheets and data processing. Choose Save PDF for a printable browser report.