Dew point calculator with heat index and wind chill

One calculator for dew point, humidity and feels-like temperature

This dew point calculator also works the other way round as a relative humidity calculator, gives the feels like temperature (heat index in summer, wind chill in winter) and checks whether a wall or window will collect condensation. It starts in °F and mph; °C, km/h, m/s and knots are one click away.

How to use it

1. Pick “Dew point”, “Relative humidity”, “Feels like” or “Condensation”, and a unit under “Temperatures in”.
2. Fill in “Air temperature” and “Relative humidity (%)” to see the result and its details.
3. “Copy link” reopens the same calculation.

Dew point and relative humidity in plain words

Warm air can hold more water vapor than cold air. Relative humidity says how much of that maximum is there. Cool the air and the humidity climbs to 100%: that temperature is the dew point. Any colder and the vapor turns into droplets: that is why a cold can “sweats” in summer.

Example: at 68 °F and 50% humidity, the dew point is 48.7 °F (9.3 °C), and each cubic meter of air holds 8.6 g of water. Going the other way, 77 °F with a dew point of 59 °F means 53.8% relative humidity. Magnus formula, coefficients 17.625 and 243.04 °C, valid from −40 to 122 °F.

Why humid air feels hotter

Sweat cools you as it evaporates. In moist air it evaporates slowly, so you feel hotter than the thermometer reads. As a guide: below 55 °F the air feels dry, from 55 to 65 °F it gets sticky, and above 65 °F it feels muggy.

Heat index calculator and wind chill calculator

The heat index combines temperature and humidity using the National Weather Service regression (Rothfusz), its adjustments for very dry and very humid air, and its simple formula for low values. It only applies from 80 °F (26.7 °C); below that, the tool shows no value. At 90 °F and 70% humidity it gives 105.9 °F, which the official chart rounds to 106 °F.

Wind chill describes how fast wind draws heat from bare skin. The 2001 formula shared by the United States and Canada applies at 50 °F or colder with wind of at least 3 mph, measured 33 feet above ground. At 0 °F with a 15 mph wind, it feels like −19.5 °F.

The optional Canadian humidex reads 41.2 at 86 °F and 70%. These categories are a general guide, not medical advice. In a heat wave or cold snap, follow local authorities' advice.

Condensation at home

A wall, window or ceiling colder than the room's dew point gets wet. In a room at 68 °F and 60%, the dew point is 53.6 °F: a wall at 54 °F is right on the edge, and the tool flags the risk. Above 80% humidity at the wall surface, mold can grow even without droplets.

With “estimate it from insulation”, the tool uses a general, cautious formula, Ts = Ti − U × 0.25 × (Ti − To): an uninsulated wall (U = 1.5) between a 68 °F room and 32 °F outside drops to about 54.5 °F.

In a basement, humid summer air at 82 °F and 60% has a dew point of 66.7 °F and condenses on 57 °F walls, so air it out early in the morning. To keep humidity down: ventilate daily, run the bathroom fan after showers, heat evenly and insulate cold walls.

Limits

These formulas are empirical and assume air in the shade; direct sun feels much hotter.

Frequently asked questions

What is the difference between relative and absolute humidity?

The first is a percentage of the maximum; the second is grams of water per cubic meter.

Why is there no heat index at 60 °F?

Below 80 °F the formula does not apply, so the tool shows no misleading value.

Can the dew point be higher than the temperature?

No. It equals the temperature when the air is saturated, at 100%.

What indoor humidity should I aim for?

Usually 40 to 60% in living spaces.