Heat adjustment calculator

Heat and humidity slow everyone down. Enter the forecast and your planned pace to see a realistic adjusted target.

Planned pace per km
Temperature
Race distance
Show pace per
Adjusted pace
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Dew point
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Temp + dew point (°F)
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Expected slowdown

Free Race Pace Plan

Turn this result into a full Race Pace Plan. Tell us your race and goal time. You get one PDF with:

  • Goal pace and splits for your race
  • Training paces for all five zones
  • A printable pace band

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How the adjustment works

Dew point measures how much moisture is in the air, and it decides how well sweat can cool you. The calculator adds the temperature and the dew point in Fahrenheit and looks up the slowdown on a widely used runner's rule of thumb: no change up to 100, about 1 % at 120, 3 % at 140, 6 % at 160 and 10 % at 180.

Above 180, hard running is not recommended. There is no official formula, so treat the result as a starting point and adjust by feel.

Common questions

Why dew point instead of humidity?

Relative humidity changes through the day as temperature changes. Dew point stays steadier and better reflects how hard it is to cool down.

Does acclimatization help?

Yes. Ten to fourteen days of training in the heat improves sweating and plasma volume, and reduces the slowdown.