Heat & humidity pace calculator
Slow your goal pace for temperature and humidity using the same coefficients many elite coaches apply: ~0.4% per °F above 60°F (15.6°C) plus 0.2% per % relative humidity above 60%. Includes heat index and a simple risk level. Defaults to min/km and °C.
Your goal
Adjusted for conditions
Run by effort or heart rate in heat; hydrate and fuel more than in cool weather. This is an educational estimate—not medical advice. Pair with our target heart rate calculator and running pace calculator.
Frequently asked
How much does heat slow my pace?
About 0.4% per °F (0.72% per °C) above 15.6°C / 60°F. At 29°C (~85°F) that is roughly 10% slower than ideal conditions for the same effort.
How does humidity affect performance?
Humidity reduces evaporative cooling. Pace slows ~0.2% per % humidity above 60%. Dew point above 18°C (65°F) is where many runners feel a hard hit.
What heat index is dangerous for running?
Above 32°C (90°F) index: caution. Above 39°C (103°F): dangerous. Above 52°C (125°F): extreme—do not run outdoors.
Should I always slow down in heat?
Yes. Holding cool-weather pace in heat raises core temperature and heat-illness risk. Start earlier, shade routes when possible, and adjust expectations.