Tag Archives: Heat Index

The ideal running temperature vs most people’s ideal temperature

One thing I find annoying is right before a relatively warm race when the obnoxious race emcee says, “It’s a perfect day outside for a race!” You can clearly tell from such a statement that the guy never runs, ever.

Because while 60-70°F (15-20°C) feels amazing if you’re out for an easy walk, or laying out in the sun… that temperature enters the somewhat-warm zone for distance runners in a race, who are moving a lot faster than a walk and producing a lot of body heat throughout their run. Add in substantial humidity, which interferes with the evaporation of sweat, and now it begins to feel really hot.

Jonathan Savage created a ‘perceived heat index for runners’ calculator to accurately show what a runner’s “heat index” is for a given pace at their height and weight, depending on the temperature and humidity. All temperatures are in Fahrenheit (the calculator on the site can be adjusted to Celsius).

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As you can see, 65°F (18°C) at even a mild 40% humidity can feel like 101°F (38°C) for a runner my size (5’10”, 160 lbs) running at a 9:05/mile pace.

To be fair, that’s mild compared to how most of the summer has felt for me, running in 80-95°F (25-35°C) afternoons with 60-75% humidity. Even running at slower paces, my heat indices this summer have been in the 130-145°F (55-60°C) range.

Needless to say, that prepares me fairly well for the worst heat the Chicago Marathon could offer me.

In any case, I’m not big on clapbacks or “educating” people, but the next time someone attempts to point out that 60+°F weather (15+°C) is perfect running weather, you may want to throw some knowledge at them about how running changes everything.

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