raceIQ

Heat pace calculator

Enter your goal and the race-morning weather to see how much to slow your pace, using the temperature-plus-dew-point rule raceIQ uses to adjust every race's predictions.

Enter the temperature and humidity for the start of your race.

The rule: temperature + dew point
Temperature + dew point (°F)Slower by
100 or lessNo change
101–1100.5%
111–1201%
121–1302%
131–1403%
141–1504.5%
151–1606%
Over 1608% or more; consider not racing for time

A rule of thumb for recreational runners, not a physiological model. People acclimatized to heat slow down less.

Common questions

How much does heat slow down running?

Very little until it's warm and humid. By the common temperature-plus-dew-point rule, nothing changes until the two add up to about 100°F; at 121 to 130 expect about 2% slower, and above 150 about 6% or more. Even 2% is almost 5 minutes on a 4-hour marathon.

Why use dew point instead of humidity?

Dew point measures how much moisture is in the air, which is what limits how well sweat cools you. Relative humidity changes through the day as the air warms even when the moisture doesn't. This calculator works out the dew point from the temperature and humidity you enter.

How should I pace a hot race?

Start at the adjusted pace rather than your goal pace and hold it; the heat costs more the longer you run, so a fast start hurts more than in cool weather. Drink early, and take the first miles easier than feels necessary.

Every race on raceIQ shows its typical race-morning weather. Your predicted placing is already adjusted for it.

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