How this calculator works
The ACSM running equation estimates oxygen use as 0.2 mL/kg/min per metre per minute of speed, plus 0.9 mL/kg/min per metre per minute for each unit of grade, plus 3.5 mL/kg/min for resting. At 200 m/min, or 12 km/h, that is 43.5 mL/kg/min on the flat. Oxygen use is converted to calories by multiplying by body mass and by 5 kcal per litre of oxygen. The equation fits steady running on a treadmill or a measured course. Wind, heat, trail surface, stops at traffic lights and the extra cost of accelerating all raise the true value.
Formula
Speed (m/min) = distance / time in minutes. VO2 (mL/kg/min) = 0.2 x speed + 0.9 x speed x grade + 3.5. kcal/min = VO2 x body mass (kg) x 5 / 1000. Calories = kcal/min x minutes.
Worked example
An 80 kg runner covers 10 km in 50 minutes on the flat. Speed is 200 m/min, VO2 is 40 + 0 + 3.5 = 43.5 mL/kg/min, and energy use is 17.4 kcal/min, or 870 kcal for the run. A 70 kg runner covering 5 km in 25 minutes at a 2 percent grade: VO2 = 40 + 3.6 + 3.5 = 47.1, giving 16.485 kcal/min and 412.1 kcal.
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Frequently asked questions
Why does grade matter so much?
Running uphill lifts your body mass against gravity on every stride. A 1 percent grade adds 0.9 mL/kg/min per metre per minute, so a small incline produces a measurable increase in energy cost.
Does the treadmill incline match outdoor grade?
Roughly. A treadmill percentage grade is rise over run, the same as the outdoor measure. Running outside also involves wind and uneven ground, so indoor and outdoor totals will not match exactly.
Why is this different from the treadmill readout?
The readout often uses a proprietary formula and may not know your body mass. The ACSM equation is a published physiological model, and it can still differ from your actual metabolism by 10 to 15 percent.