Heat-Adjusted Pace Calculator
Heat and humidity make every pace slower at the same effort, and the culprit is dew point, not just the thermometer. Add air temperature to dew point: a higher sum means a bigger pace penalty. An 8:00 per mile goal in hot, humid conditions can realistically become 8:30 or more for the exact same effort.
Enter your goal pace and the conditions to get a realistic adjusted pace, the seconds per mile you should expect to lose, and a heat-stress zone. We call the output your Heat-Adjusted Pace Plan.
Enter your goal pace, temperature, and humidity and hit calculate. Your heat-adjusted pace, per-mile slowdown, and heat-stress zone appear here.
Gear up
Heat-running gear athletes actually buy
In the heat you run by effort, drink early, and cool aggressively. Test any new hydration strategy in training first.
- Heart rate chest strap monitorIn heat you must run by effort, not pace. A chest strap gives the accurate heart rate to cap easy days.View on Amazon →
- Insulated handheld running bottleCarry cold fluid on hot runs so you can drink early and often instead of waiting for fountains.View on Amazon →
- Cooling towel / ice bandanaPre-cool the neck and wrists before and during the run to blunt the heart-rate drift heat causes.View on Amazon →
- High-sodium electrolyte drink mixHot, humid runs raise sweat rate and sodium loss. Replace it to hold pace and avoid cramps.View on Amazon →
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Run by effort?
Heart Rate Zone Calculator
Get the heart-rate ceilings to cap your easy and long runs when heat pushes pace off target.
Sweating more?
Sodium Calculator
Hot, humid runs raise sweat and sodium loss. Get your per-hour replacement target so you can hold pace.
Heat-adjusted pace FAQ
Why is my pace slower in summer?
In the heat your body sends more blood to the skin to shed heat, which leaves less for your working muscles. To hold the same internal effort your heart rate climbs and your pace falls. The hotter and more humid it is, the bigger the penalty. This is normal physiology, not lost fitness. Running by effort and accepting a slower pace is the correct response, and this calculator estimates exactly how much slower your goal pace should be today.
What is dew point and why does it matter for running?
Dew point is the temperature at which the air becomes fully saturated with moisture. It is a far better gauge of how oppressive conditions feel than humidity alone, because humidity changes through the day while dew point stays fairly stable. A high dew point means your sweat cannot evaporate efficiently, so you lose your main cooling system. That is why a 75F morning at a 70F dew point can feel harder than a dry 90F afternoon, and why this tool adds temperature and dew point together.
How much should I slow down in the heat?
A practical rule is to add the air temperature (F) and the dew point (F), then apply a pace penalty that rises with that sum. Below 100 there is no penalty; around 120 to 129 expect about 2 percent slower; from 150 to 159 about 6 percent; and at 180 and above roughly 12 percent or more, where running outdoors becomes risky. For an 8:00 per mile goal pace, a 6 percent penalty is nearly 30 seconds per mile. The calculator does this math for your exact conditions.
Should I use pace or heart rate to run in the heat?
Use effort, measured by heart rate or perceived exertion, not pace. Heat makes your heart rate drift up at any given speed, so chasing a fixed pace forces you into a harder effort than planned. Cap your easy and long runs by heart rate or RPE and let pace land where it lands. Save hard pace-based work for cooler hours or move it indoors. The slower adjusted pace this tool shows is what the same effort should produce today.
Does humidity or temperature matter more?
Both matter, and the dew point captures the humidity side. On a hot, humid day your sweat does not evaporate, so you keep sweating without cooling and your core temperature climbs. That is why two days at the same air temperature can feel completely different. By combining temperature with dew point, this calculator weighs both at once instead of relying on the thermometer alone.
See also: why your easy runs should be easier.
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