Running Calculator

Running Calculator › Heat Pace Calculator

Heat Pace Calculator

Enter your planned pace plus temperature and humidity – the calculator shows how much slower you should run.

Planned pace (in cool weather)
Temperature
HumidityIn humid air your sweat evaporates poorly and barely cools you – the same temperature becomes much harder. Any weather app shows the value.
Adjusted pace
8:43/mi
8:40–8:45Range
+2–3 %Adjustment
62 °F
Dew pointThe temperature at which the air would be saturated with water vapor. The higher the dew point, the muggier it feels: from about 60 °F it gets noticeably sticky.

Temperature + dew point = 139 °F. Heat-acclimatized runners can use the lower end of the range, everyone who struggles in the heat the upper end.

Why you should run slower in the heat

Running produces a lot of heat. To keep from overheating, your body sends more blood to the skin and you sweat. That blood is missing in your muscles, and sweat only cools you if it can evaporate – which works poorly in humid air. Your heart rate climbs and the same pace feels much harder. Stubbornly sticking to race pace usually ends in a fade over the second half.

An analysis of seven major US marathons (Ely et al., 2007) shows that finish times get slower as heat stress rises – by several percent even for the fastest runners, and slower runners tend to lose even more.

How the calculator works

We use the rule of thumb by US running coach Mark Hadley that's popular with runners: add the temperature and the dew point, both in °F. The dew point describes how much moisture is in the air – the calculator derives it from temperature and humidity. The higher the sum, the bigger the adjustment to your pace:

Temperature + dew point (°F)Pace adjustment
up to 100no adjustment
101–1100–0.5 %
111–1200.5–1 %
121–1301–2 %
131–1402–3 %
141–1503–4.5 %
151–1604.5–6 %
161–1706–8 %
171–1808–10 %
over 180hard running not advised

Adjustment by temperature and humidity

The same chart converted to temperature and relative humidity:

Temperature30% humidity50% humidity70% humidity90% humidity
15 °C––+0–0.5 %+0.5–1 %
20 °C+0–0.5 %+0.5–1 %+1–2 %+2–3 %
25 °C+0.5–1 %+2–3 %+3–4.5 %+4.5–6 %
30 °C+2–3 %+4.5–6 %+6–8 %+6–8 %
35 °C+4.5–6 %+6–8 %+8–10 %not advised
Temperature30% humidity50% humidity70% humidity90% humidity
60 °F–+0–0.5 %+0–0.5 %+0.5–1 %
65 °F–+0.5–1 %+0.5–1 %+1–2 %
70 °F+0–0.5 %+0.5–1 %+1–2 %+2–3 %
75 °F+0.5–1 %+1–2 %+2–3 %+3–4.5 %
80 °F+1–2 %+2–3 %+3–4.5 %+4.5–6 %
85 °F+2–3 %+3–4.5 %+4.5–6 %+6–8 %
90 °F+3–4.5 %+4.5–6 %+6–8 %+8–10 %
95 °F+4.5–6 %+6–8 %+8–10 %not advised

Tips for running in the heat

For a race, plan the heat right in the split calculator – it then gives you heat-adjusted splits.

More calculators

SplitsPlan your splits & print a pace bandMarathonPace and splits for the marathonTraining PacesEasy, threshold & interval pacesPace ConverterConvert speed to pace and back

FAQ

How much slower should I run in the heat?

It depends on temperature and humidity. At 77 °F and 60% humidity, the Hadley chart suggests about 2–3% – an 8:30 per mile pace becomes roughly 8:43 per mile.

What is the dew point?

The dew point is the temperature at which the air would be saturated with moisture. The higher it is, the muggier it feels and the less your sweat cools you. Many weather apps show it directly.

At what temperature should I adjust my pace?

Once temperature plus dew point adds up to more than 100 °F, an adjustment is worth it – for example at 65 °F and 60% humidity.

Does the adjustment apply to intervals?

For short repeats up to about half a mile, half the adjustment is usually enough because you cool down during the recoveries.