How this calculator works
The ACSM walking equation estimates oxygen use from speed and slope. The horizontal term is 0.1 mL/kg/min for each metre per minute of speed, the grade term is 1.8 mL/kg/min per metre per minute for each unit of slope, and resting adds 3.5 mL/kg/min. A 5 percent uphill raises the cost noticeably; a downhill slope reduces the grade term, although steep descents can increase the true cost through eccentric muscle work. The equation assumes walking, not running, and a steady pace. Use the running calculator for speeds above about 8 km/h.
Formula
Speed (m/min) = distance / time in minutes. Slope is entered as a percentage and used as a fraction. VO2 (mL/kg/min) = 0.1 x speed + 1.8 x speed x slope + 3.5. kcal/min = VO2 x body mass (kg) x 5 / 1000. Calories = kcal/min x minutes.
Worked example
A 70 kg person walks 5 km in 60 minutes on the flat: speed is 83.33 m/min, VO2 is 8.33 + 0 + 3.5 = 11.83 mL/kg/min, and energy use is 4.14 kcal/min, or 248.5 kcal. At a 5 percent slope the grade term adds 7.5 mL/kg/min, VO2 becomes 19.33 and the total rises to 406 kcal.
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Frequently asked questions
Does walking downhill burn fewer calories?
The equation gives a lower cost for a negative grade, so the estimate falls. Real downhill walking uses eccentric muscle work that can add some cost, especially on steep descents, so the equation is least accurate there.
Why enter time as well as distance?
Speed is distance divided by time, and both the horizontal and grade terms depend on speed. A slow walk and a fast walk over the same distance use different amounts of energy per minute.
Is walking or running better for burning calories?
Running burns more per minute but usually less per kilometre than walking, because walking takes longer. Per kilometre travelled the difference is modest. Total energy use still depends mainly on distance and body mass.