Dew Point Calculator: Humidity & Comfort

Reading your dew point results

In dew-point mode the headline is dew point in your preferred unit; in humidity mode it is relative humidity (%). The comfort-scale badge always uses dew point; technical conversions list °C, °F, and kelvin.

Example: 25 °C, 60% relative humidity

Defaults: Calculate for: Dew point, air 25 °C (77 °F), relative humidity 60%. Dew point ≈ 16.7 °C (62 °F). Comfort scale: Muggy (15–21 °C band). Technical conversions show kelvin ≈ 290 K.

Calculate for and unit preference

Section 01 Calculate for toggles dew-point mode (temperature + RH) vs relative-humidity mode (temperature + dew point). Unit preference highlights °F or °C in the headline; Decimal places rounds the results panel and conversion rows.

Comfort scale and technical conversions

The badge color follows dew point: green (dry), teal (comfortable), yellow (muggy), red (oppressive). The Technical conversions block lists the same dew point in °C, °F, and K whenever a valid dew point exists—including in humidity mode when you entered dew point directly.

Dew point calculator: humidity, comfort scale, and Magnus-Tetens

This page computes dew point from air temperature and relative humidity, or relative humidity from air temperature and dew point, using the Magnus-Tetens approximation. Comfort badge from dry through oppressive; not a substitute for a calibrated weather station.

What this calculator does

Enter air temperature (°F or °C, synced both ways) and either relative humidity (1–100%) or dew point, depending on the Calculate for mode. You get dew point or relative humidity in the results panel, a comfort-scale badge, and technical conversions in °C, °F, and kelvin. Dew point is the temperature at which air saturates and moisture condenses—unlike relative humidity alone, it tracks actual moisture content. This tool uses the Magnus-Tetens water-vapor approximation; it does not compute heat index, wind chill, or pressure-altitude corrections.

How the math works

Magnus-Tetens approximation. First compute

\gamma(T, RH) = \ln(RH/100) + \frac{bT}{c+T}

where T is air temperature (°C) and RH is relative humidity (0–100). Then

T_d = \frac{c\gamma}{b - \gamma}

gives dew point T_d in °C. Constants: b = 17.625, c = 243.04. To find relative humidity from T and dew point, use

\gamma = \frac{bT_d}{c+T_d}

and

RH = 100 \cdot e^{\gamma - \frac{bT}{c+T}}

Valid when dew point does not exceed air temperature.

Limits of the model

Comfort bands on the badge (dry below 10 °C, comfortable 10–15 °C, muggy 15–21 °C, oppressive above 21 °C) are rule-of-thumb outdoor feel—not medical guidance. For hot-day feels-like temperature, see the Heat Index Calculator; for cold wind effects, see the Wind Chill Calculator.

Dew Point Calculator FAQ

How do I get dew point from temperature and humidity on this page?

Leave Calculate for on Dew point, enter air temperature in °C or °F (fields sync), set relative humidity with the slider or number box (1–100%), and read dew point in the results headline plus the comfort-scale badge and technical conversions.

How do I find relative humidity from dew point?

Switch Calculate for to Rel. humidity, enter air temperature and observed dew point in synced °C/°F fields, and read relative humidity (%) in the results panel. The tool inverts the same Magnus-Tetens approximation used in dew-point mode.

What does the comfort scale badge mean?

The badge maps dew point to how humid it feels: Dry below 10 °C (50 °F), Comfortable 10–15 °C (50–60 °F), Muggy 15–21 °C (60–70 °F), and Extremely Humid / Oppressive above 21 °C (70 °F). It updates whenever a valid dew point is available in either mode.

Do °C and °F inputs affect each other?

Yes. Air temperature and dew point each sync both ways using

F = 1.8C + 32

. Type in either field; the paired unit updates. Unit preference only changes which column is highlighted and which unit leads in the results headline.

Why is there no result in humidity mode?

Dew point cannot exceed air temperature. If dew point input is warmer than air temperature, or relative humidity is outside 1–100% in dew-point mode, the results panel stays empty until the values are physically consistent.

What formula and constants does this calculator use?

Magnus-Tetens approximation with b = 17.625 and c = 243.04 (°C). Dew point from temperature and RH; relative humidity from temperature and dew point. Ideal-gas water-vapor model—not a full psychrometric chart or calibrated station reading.

Sources & citations

References used for the calculation method and definitions. Links open in a new tab when available.

[1]

NOAA National Weather Service Glossary — Dew Point (DWPT)

Official glossary entry: dew point is the temperature to which air must be cooled to reach saturation at constant pressure and moisture content; a higher dew point means more moisture in the air.

[2]

Lawrence (2005) — Relative humidity and dew point in moist air (BAMS)

Bulletin of the American Meteorological Society article on converting between relative humidity and dew point; documents the Magnus-form coefficients used in this calculator, including 17.625 for the vapor-pressure fit paired with 243.04 °C.

Mathematical Reference Note

Calculation Logic: This tool uses standard mathematical algorithms. While we strive for accuracy, errors in logic or user input can result in incorrect data.

Verification: Results should be cross-checked if used for important academic, professional, or personal calculations.

Standard Terms: This tool is provided free of charge and as-is. CalcRegistry provides no warranty regarding the accuracy or fitness of these results for your specific needs.

Dew Point Calculator: When Moisture Condenses

Settings

Air temperature

Relative humidity

How to use this calculator