New app for calculating heat-adjusted paces

screenshot of heat adjusted pace calculator app

I just finished up a new app for calculating the effects of heat and humidity on workout and race paces—a “heat-adjusted pace.” 

☀️ Check out my new heat-adjusted pace calculator here! 🌡️

This app builds on the work I wrote about in a post earlier this year on heat and humidity’s effects on marathon performance.

This web app uses a statistical model fit to nearly 4,000 marathon performances to estimate the effects of both heat and humidity on race and workout times. You can enter weather conditions as a heat index, temperature and relative humidity, or temperature and dew point.

Although the app is built on data from marathon races, it’s also useful for long tempo runs, easy runs, and other long sessions in the heat. 

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Calculating the effects of heat and humidity on marathon performance

How much does heat and humidity affect performance in the marathon? And how do we know how much those conditions affect marathon performance? These questions matter both for planning what marathon race you want to sign up for as well as for adjusting your pacing plan the week of the race once the weather forecast finalizes.

Below, I’ll make the case that the optimal temperature for marathoning is 35–55 degrees F, or 2–13 degrees C. Additionally, I’ll show that humidity is not a concern until the air temperature is above 65° F (18° C). These numbers come from an analysis of 3,891 marathon performances across 754 different races.

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Check out my new book on marathon training!