Heat-Adjusted Pace Calculator
Estimate the equivalent effort in ideal weather for a pace you ran in the heat — or see how much you may need to slow down as temperature and humidity rise.
5:00/km at 27°C, 50% humidity
27°C · 50%
Ideal-weather Pace 4:52/km
How to use it
Select Heat pace → Cool to estimate the equivalent effort of a recent pace in the heat, or Cool effort → Heat pace to adjust a target pace to expected weather conditions. Enter temperature and relative humidity, or the Heat Index from your weather app.
What you need to know
The result is an average statistical estimate based mainly on marathon performances and continuous endurance efforts. It does not fully account for individual heat acclimatisation, direct sunlight, shade, wind, clothing or hydration. In extreme heat or humidity, safety takes priority over any target pace.
In the heat, adjust pace while keeping your target intensity.
The effort needed for a given pace changes as temperature and humidity rise. Together, we can adapt your sessions and pacing to actual weather conditions, so you do not have to chase paces that no longer match the session’s target intensity.
Methodology & Sources
This implementation adapts John J. Davis’s statistical model from the Running Writings Heat-Adjusted Pace Calculator. The model uses 3,891 marathon performances from 754 races, selected from the wider dataset in the research by Mantzios et al. Temp + RH mode uses bilinear interpolation of temperature and relative humidity. Heat Index mode is based on the US National Weather Service Heat Index and the Rothfusz equation. Heat Index is a more indirect approach and may be less accurate than entering temperature and relative humidity directly. The result estimates an average effect, not an individual prediction.
Last updated: 30 August 2026