Tool
Dew Point Calculator
Enter a temperature and relative humidity to get the dew point — or go the other way and find what humidity a given dew point implies. Both directions use the Magnus-Tetens formula.
Quick answer
Enter a value above — the result appears here with what it feels like.
Uses the Magnus-Tetens formula, the same approximation meteorologists use. The shortcut Td ≈ T − ((100 − RH) / 5) is close above roughly 80% humidity but drifts badly below that.
How to Use the Dew Point Calculator
Pick the direction you want first. Temperature + humidity → dew point is the common case: you have a thermostat or weather app reading and want to know what the moisture actually feels like. Temperature + dew point → humidity is the reverse — useful when a forecast quotes the dew point and you want the percentage.
Units switch between °F and °C and apply to every field at once, including the result. Values are computed on the fly in your browser — nothing is sent anywhere, and there’s no page reload.
The Formula Behind It
The calculator uses the Magnus-Tetens approximation, which is accurate to within a fraction of a degree in normal weather ranges. In Celsius:
α = ln(RH / 100) + (17.27 × T) / (237.7 + T)
Td = (237.7 × α) / (17.27 − α)The much-quoted shortcut Td ≈ T − ((100 − RH) / 5) is fine in very humid conditions and misleading in dry ones. At 85°F and 60% humidity it returns about 77°F — roughly 7°F too high. That gap is why the full equation is worth using.
See the step-by-step worked example →
Want the whole lookup table instead of one calculation? The dew point temperature chart covers every temperature from 60°F to 100°F at 30–90% humidity.
What the Result Means
The calculator labels every result with a comfort band, so you don’t have to translate the number yourself. The bands are the same ones used in the dew point comfort chart: below 10°C (50°F) is dry, 10–16°C (50–60°F) is comfortable, 16–21°C (60–70°F) turns sticky, and above 21°C (70°F) is oppressive.
One caveat the bands can’t capture: dew point sets the floor on how muggy it feels, but the air temperature decides how bad it gets. A 21°C dew point at 24°C air temperature is sticky; the same 21°C dew point at 35°C stacks a brutal heat index on top.
Why Not Just Use Relative Humidity?
Because the same percentage means different things at different temperatures. 50% humidity at 60°F feels dry; 50% at 90°F feels oppressive. Relative humidity is a ratio that moves whenever the temperature moves — even with no moisture added or removed. Dew point is absolute: a 65°F dew point always feels sticky, whether it’s morning or afternoon.
Read the full dew point vs humidity comparison →
Need humidity from a wet bulb reading? Use the Wet Bulb Calculator →
Frequently Asked Questions
What is a good dew point?
Between 50°F and 60°F (10–16°C) for most people. Below 50°F feels dry, above 60°F starts to feel sticky, and above 70°F feels oppressive.
Can dew point be higher than the temperature?
No. Dew point is always at or below the air temperature, because it's the temperature at which the air would become saturated. When the two are equal, relative humidity is 100% and fog or condensation is forming. If a calculator returns a dew point above the temperature, one of your inputs is off.
Is this the same formula weather apps use?
Close enough to match them to the nearest degree in ordinary weather. The Magnus-Tetens approximation is the standard for consumer weather products; research and aviation use more elaborate formulations that differ by a few tenths of a degree.
← Back to the dew point chart · See what each number feels like →