Free pace calculator
How Much to Slow Down in Heat and Humidity
Enter the temperature, the dew point (or humidity), and the pace you run in cool air. The calculator gives the pace that matches the same effort in these conditions, from the same pace model the RunWeather app uses.
Your run
Aim for
9:43 /mi
+0:43 /mi
The same effort as your cool-air pace, in these conditions. Let the pace fall there and keep the effort where it belongs. Heat strain is real at this level: drink before you go and watch for heart rate drift.
Heat and humidity pace chart
Extra time per mile for a 9:00 per mile (5:36 per km) easy hour in shade or overcast sky, by air temperature and dew point. Full sun and harder efforts slow you more. Use the calculator above for your own pace, effort, and sun.
| Air temp | Dew 45°F7°C | Dew 50°F10°C | Dew 55°F13°C | Dew 60°F16°C | Dew 65°F18°C | Dew 70°F21°C | Dew 75°F24°C |
|---|---|---|---|---|---|---|---|
| 60°F16°C | +0:05 | +0:11 | +0:11 | +0:16 | |||
| 65°F18°C | +0:11 | +0:11 | +0:16 | +0:16 | +0:22 | ||
| 70°F21°C | +0:16 | +0:16 | +0:16 | +0:22 | +0:27 | +0:32 | |
| 75°F24°C | +0:16 | +0:22 | +0:22 | +0:27 | +0:32 | +0:43 | +1:05 (unsafe heat) |
| 80°F27°C | +0:22 | +0:22 | +0:27 | +0:27 | +0:32 | +0:49 | +1:10 (unsafe heat) |
| 85°F29°C | +0:27 | +0:27 | +0:27 | +0:32 | +0:38 | +0:49 | +1:16 (unsafe heat) |
| 90°F32°C | +0:27 | +0:32 | +0:32 | +0:38 | +0:43 | +0:54 | +1:16 (unsafe heat) |
| 95°F35°C | +0:32 | +0:32 | +0:38 | +0:38 | +0:43 | +0:59 (unsafe heat) | +1:21 (unsafe heat) |
Red: unsafe heat stress, move the run. Blank: the dew point cannot be higher than the air temperature. Numbers from RunWeather's pace model at constant effort, not measured race results.
Read the chart by dew point first
Read across any row and the slowdown climbs slowly until the dew point passes about 65°F (18°C), then jumps. That is the point where sweat stops evaporating fast enough to keep you cool, so the same pace takes more and more of your heart rate. Air temperature matters too, but far less per degree than dew point.
For the full picture of how to train through a hot block, including workouts and long runs, read the heat and humidity pace adjustment guide and why dew point matters for running. To check today's conditions where you live, the Run Score calculator scores every hour of the forecast, and Heat Risk Today ranks 57 cities by heat stress right now.
Running in heat and humidity: FAQ
How much should I slow down running in the heat?
For an easy run in shade, expect roughly 10 to 40 seconds per mile once the dew point passes about 55°F (13°C), and more than a minute per mile when the dew point reaches the mid 70s. Full sun adds more on top. The table on this page shows the slowdown for a 9:00 per mile easy run across temperature and dew point.
Why does this calculator ask for dew point instead of temperature alone?
Your body cools by evaporating sweat, and dew point measures how much moisture is already in the air. Above about 60°F (16°C) dew point, sweat evaporates slowly, so heat builds up at the same pace. Two days at 80°F can need very different paces: one with a 50°F dew point barely slows you, one with a 72°F dew point slows you far more.
Can I use relative humidity instead of dew point?
Yes. Switch the moisture field to humidity and the calculator converts it to dew point from the air temperature using the Magnus formula. Dew point is the better number to remember, because relative humidity changes through the day as the air warms even when the moisture in the air stays the same.
Does the slower pace mean I am losing fitness?
No. The pace shown is the same effort as your cool-air pace, in hotter air. Heart rate and breathing tell you the effort; the pace is what the weather lets that effort produce. When the weather cools, the old paces come back at the same effort.
Where do these numbers come from?
It is RunWeather's own pace model, the same one the app uses to put a weather-adjusted pace next to every run. It estimates heat strain from wet-bulb globe temperature (air temperature, dew point, and sun) and scales it by effort and run length. It is a model, not a measurement of you: heat-acclimated runners slow less, and heat-sensitive runners slow more.
When is it too hot to run at all?
When estimated heat stress reaches the unsafe tier, the calculator flags it in red, and so does the chart. The slower pace still describes the same effort, but no pace makes that run safe: move it to a cooler hour or indoors, or keep it short, run by effort, and stop at the first sign of dizziness, chills, or confusion.
Get this on every run, automatically
RunWeather syncs with Strava, plans your week, and learns your heat tolerance, so the right time to run finds you. Free on iPhone and Android.
Running weather guides
How each kind of weather changes your run, and the cities where it matters most.