Enter values
Example data table
Sample inputs and typical outputs for quick checking.
| Air temperature (°C) | Relative humidity (%) | Dew point (°C) | Spread (°C) | Actual vapor pressure (hPa) |
|---|---|---|---|---|
| 25 | 60 | ≈ 16.7 | ≈ 8.3 | ≈ 19.0 |
| 10 | 90 | ≈ 8.5 | ≈ 1.5 | ≈ 11.0 |
| 35 | 40 | ≈ 19.6 | ≈ 15.4 | ≈ 22.5 |
Formula used
Dew point is the temperature where air becomes saturated at the current water vapor amount. This calculator first estimates saturation vapor pressure es, then finds actual vapor pressure e, and finally solves for dew point Td.
Magnus method
γ = ln(RH/100) + (a·T)/(b+T)
Td = (b·γ)/(a−γ)
Uses a=17.62 and b=243.12°C for water vapor.
Arden Buck method
es = 6.1121·exp[(18.678 − T/234.5)·T/(257.14+T)]
e = (RH/100)·es
Dew point is obtained by inverting the vapor-pressure relation.
Absolute humidity is estimated as 216.7·e/(T+273.15) in g/m³, with e in hPa and T in °C.
How to use this calculator
- Measure air temperature and relative humidity with a sensor.
- Select the unit that matches your temperature reading.
- Choose a method, then set your preferred rounding.
- Press Calculate to view dew point and related quantities.
- Use the download buttons to export your computed results.
- Interpret spread values to assess condensation or fog likelihood.
Professional notes on dew point analysis
1) Measurement inputs and units
Dew point depends on two direct measurements: air temperature and relative humidity. Most sensors report temperature in °C or °F and humidity from 0–100%. For consistent physics, the calculator converts temperature internally to °C before applying the chosen vapor-pressure model.
2) Dew point versus relative humidity
Relative humidity changes strongly with temperature, even if the water vapor amount stays the same. Dew point tracks the actual moisture content more directly, so it is often preferred for field reporting, safety planning, and process control where “how much water vapor is present” matters.
3) Why two methods are offered
The Magnus family uses a compact logarithmic form that performs well for everyday atmospheric ranges. The Arden Buck formulation is widely used in meteorology because it fits saturation vapor pressure with a refined exponential expression. Comparing both helps spot sensitivity when data are near saturation.
4) Vapor pressure outputs with real meaning
Saturation vapor pressure es increases rapidly with temperature. Actual vapor pressure e is estimated by multiplying es by RH/100. These quantities explain why a warm day can feel dry at moderate RH while still containing substantial moisture.
5) Dew point spread as a quick risk indicator
The spread (T − Td) is a practical condensation signal. Spreads below about 2–3°C often coincide with haze, fog, or surface condensation under calm conditions. Larger spreads typically indicate lower near-surface saturation risk.
6) Comfort and operational thresholds
Many practitioners use dew point bands to communicate discomfort: below ~10°C feels dry, ~10–16°C often feels comfortable, ~16–20°C feels noticeably humid, and above ~20°C can feel oppressive. HVAC setpoints and dehumidification loads are commonly discussed using dew point rather than RH alone.
7) Accuracy, calibration, and uncertainty
A ±2% RH sensor error can shift dew point by around 0.3–1.0°C depending on conditions, with larger impact near saturation. For best results, shield sensors from direct sun, allow equilibration, and validate readings using a reference instrument when precision matters.
8) Reporting and exporting results
Use the CSV export for spreadsheets, dashboards, and data logging. The PDF export is suited for lab notebooks, compliance records, and site reports. Include the method name, units, and rounding level so others can reproduce the calculation consistently.
FAQs
1) What is dew point in simple terms?
Dew point is the temperature where air becomes saturated with the water vapor it currently holds. Cooling to that point triggers condensation on surfaces or in the air.
2) Why can dew point be more useful than relative humidity?
Relative humidity changes with temperature, so it can swing during the day. Dew point tracks moisture content more steadily, making it easier to compare conditions across different temperatures.
3) Which method should I choose, Magnus or Arden Buck?
Magnus is a strong general-purpose option for typical ranges. Arden Buck is widely used in meteorology and can be preferred for detailed atmospheric work. If unsure, compare both.
4) What does a small dew point spread mean?
A small spread (T − Td) means air is close to saturation. That increases the likelihood of fog, haze, or condensation, especially overnight or with weak mixing.
5) Can dew point be higher than air temperature?
In physically consistent measurements, dew point should not exceed air temperature. If it does, the humidity reading may be biased, or the sensor may be warming/cooling unevenly.
6) How accurate are the results?
Accuracy depends mainly on sensor quality. Small RH errors can shift dew point noticeably near saturation. The formulas are standard approximations and are usually excellent for routine atmospheric calculations.
7) What is absolute humidity and why is it shown?
Absolute humidity estimates the mass of water vapor per air volume (g/m³). It is useful for ventilation analysis, drying processes, and comparing moisture levels at different temperatures.