Running in heat and humidity: pace calculator
The same effort is slower when it’s hot and humid. This shows by about how much.
The rule
Add the temperature and the dew point, both in °F. Coaches have used this rule of thumb for years to set summer paces for continuous running.
| Temperature + dew point (°F) | Pace adjustment |
|---|---|
| 100 or less | No adjustment |
| 101–110 | 0–0.5% |
| 111–120 | 0.5–1% |
| 121–130 | 1–2% |
| 131–140 | 2–3% |
| 141–150 | 3–4.5% |
| 151–160 | 4.5–6% |
| 161–170 | 6–8% |
| 171–180 | 8–10% |
| Above 180 | Hard running not advised |
An estimate for the same effort. It varies with body size, fitness, sun, wind and how used to the heat you are. Long runs and races are affected more than short ones.
Running well in the heat
- Go early. Dawn is usually the coolest air of the day, though it’s also the most humid; evenings are drier but the ground is still radiating heat.
- Shade and a breeze count. Direct sun can add the equivalent of 10–15°F.
- Drink to thirst and carry water on anything over about 45 minutes in the heat.
- Know the warning signs: chills or goosebumps in the heat, dizziness, confusion, or stopping sweating. Stop, get to shade and cool down.
For your route and start time
Route Forecast works this out for the weather along your run at the time you’ll be out, and shows it on the forecast as “+N s/mi from heat”. Open a route and choose Run.
Questions
How much does heat slow down running?
Add the air temperature and the dew point in °F. At 100 or less there’s little effect. Around 120 expect about 1% slower, around 140 about 2–3%, around 150 about 3–4.5%, and around 160 about 4.5–6% at the same effort. Above 180, hard running isn’t advised.
Why dew point instead of humidity?
Sweat cools you only when it evaporates, and the dew point tells you how much moisture is already in the air. 90% humidity at 50°F is comfortable; 60% at 85°F is not. Dew points under 55°F feel dry, 60–65°F sticky, and above 70°F oppressive.
Should I slow down or run by effort?
Run by effort (breathing or heart rate) and let the pace be what it is. The adjusted pace here is a guide to what that effort will look like on the watch, so a slower split doesn’t read as a bad day.
How long does it take to get used to heat?
Most of the adaptation happens in 10–14 days of regular running in the heat. Until then expect a bigger slowdown than the table shows.