Summer Running: Adjusting Pace for Heat & Humidity
“Why was my easy run so hard today?”
It is July. The thermometer reads 85°F. You set out for a 45-minute easy run, but your heart rate spikes, your legs feel like lead, and you finish discouraged because your pace was 30 seconds slower than normal.
You didn’t lose fitness overnight. You are just fighting physics.
When you run in the heat, your body sends blood to your skin to cool you down. That means less oxygen-rich blood is going to your working muscles. If you add high humidity (dew point), your sweat stops evaporating, and your internal temperature skyrockets.
Don’t force the pace. Smart training means keeping the effort constant, not the speed. Use the tool below to find your Temperature Adjusted Pace. If your training plan calls for a 7:30 mile, but the dew point is 70°F, this calculator will tell you exactly how much to slow down to get the same physiological benefit without overtraining.
☀️ Summer Pace Adjuster
Don’t fight the heat. Adjust your pace to maintain the correct effort level.
Switch to Humidity %
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✅ Subscribe for FreeFor runners, Dew Point is the most important metric.
Relative Humidity can be misleading. 90% humidity at 40°F feels fine. 90% humidity at 80°F is unbearable.
Dew Point measures the actual moisture in the air. It tells you how hard it will be for your sweat to evaporate. < 55°F: Great running weather. 60–65°F: You will feel it (“Sticky”). >70°F: Oppressive. Sweat drips but doesn’t cool you.
No. In fact, forcing your normal pace in high heat makes you slower in the long run. If you force a 7:00 pace when the heat index demands an 8:00 pace, you turn an “Aerobic Base” run into a “Threshold” or “Anaerobic” workout. You accumulate too much fatigue, recover poorly, and risk burning out before the fall season even starts.
Never ignore the heat, but you can ignore the specific pace if you are running by Heart Rate. If you use a heart rate monitor, simply stay in your Zone 2 (Easy) range. You will naturally slow down to the exact pace this calculator predicts!
The algorithm in the tool I built for you uses a step-function based on Dew Point, derived from a synthesis of Jack Daniels’ VDOT adjustments and the Runner’s Connect Dew Point research.
Evaporation is King: The only way humans cool down efficiently while running is sweat evaporating off the skin.
Saturation: Dew Point measures how saturated the air is.
At 50°F Dew Point, the air is dry; sweat evaporates instantly, cooling the blood.
At 75°F Dew Point, the air is already full of water. Sweat sits on the skin and drips off. Zero evaporation = Zero cooling.
Cardiac Drift: Because the blood isn’t cooling, the heart has to pump blood to the skin faster to try to dump heat. This means less blood for the legs, raising the heart rate for the same pace.