Heat Pace Adjustment Calculator
Enter the air temperature, the dew point or relative humidity, and the pace you would run in cool weather. You get the pace range that matches the same effort in the heat.
Temperature unit
Humidity as
Heat-adjusted pace
Temperature plus dew point: 141 (°F). Suggested slowdown: 3% to 4.5%.
This estimate uses a generic formula. Connect your Strava/Whoop/Garmin data for a version personalised to your actual training.
Get early accessWhy heat slows you down
In warm weather your body sends more blood to the skin to shed heat, so less is available for your working muscles, and your heart rate drifts upward at the same pace. Humidity makes it worse: sweat only cools you when it evaporates, and it evaporates poorly in moist air. That is why dew point, the absolute measure of how much moisture is in the air, matters as much as the temperature itself.
How it is calculated
This calculator uses coach Mark Hadley's temperature plus dew point guideline. Add the air temperature (°F) to the dew point (°F), then look the sum up in a band table: 100 or below needs no adjustment, and each band above that slows your pace by a bigger percentage, up to 8 to 10% for a sum of 171 to 180. Above 180, hard running is not recommended at all. Enter Celsius or relative humidity and the calculator converts for you (dew point from humidity via the Magnus formula). The result is a range, not one number, because how much heat slows you depends on your body size, fitness, and how acclimatised you are. Your target pace is multiplied by 1 plus each end of the band.
How to use the result
Use the slower end of the range for long efforts, for your first hot runs of the season, and if you are a bigger runner. Use the faster end once you are heat acclimatised (roughly 10 to 14 days of training in the heat). For short repeats with recovery in between, the effect is smaller. In every case, effort and heart rate are better guides than the clock on a hot day.
Sources and limitations: see our methodology.
Worked example
Take a runner with a goal pace of 5:00 /km on a summer morning at 30 °C (86 °F) with a dew point of 22 °C (72 °F).
Temperature plus dew point is 86 + 72 = 158, which falls in the 151 to 160 band: slow down by 4.5 to 6%. The heat-adjusted pace is 5:14-5:18 /km. Over a 10K that is roughly 2:15 to 3:00 slower than the same effort in cool weather, which is the difference between a smart race and a blow-up in the last 3 km.
FAQ
How much should I slow down when running in the heat?
Add the temperature in °F to the dew point in °F. At 100 or below, no adjustment is needed. From 101 to 120 slow down by up to 1%, from 121 to 140 by 1 to 3%, from 141 to 160 by 3 to 6%, and from 161 to 180 by 6 to 10%. Above 180, skip hard running altogether. This calculator does the conversion and lookup for you.
Why use dew point instead of humidity?
Relative humidity depends on temperature: 60% humidity at 15 °C is comfortable, at 30 °C it is oppressive. Dew point measures the actual amount of moisture in the air, so it maps much more directly onto how well your sweat can evaporate. If your weather app only shows relative humidity, switch the calculator to humidity and it will work out the dew point.
What dew point is too high for running?
Most runners start to feel it once the dew point passes about 16 °C (60 °F), and above about 21 °C (70 °F) almost everyone slows noticeably. Combined with a warm temperature, a high dew point quickly pushes the temperature plus dew point sum above 160, where the guideline already suggests slowing by 6% or more.
Does heat acclimatisation reduce the slowdown?
Yes. After roughly 10 to 14 days of training in the heat your plasma volume rises, you start sweating earlier, and your heart rate at a given pace drops. That is part of why the guideline gives a range: an acclimatised runner can use the faster end, someone on their first hot run should use the slower end.
Should I adjust interval paces for heat too?
Less than continuous runs. Short repeats with recovery give your body time to shed heat, so the adjustment is smaller, often around half. Long tempo runs, long runs, and races should get the full adjustment.