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Running Power Estimate Calculator

Estimate the watts behind your run without a power meter.

How it is calculated

Power is metabolic cost converted to mechanical output plus air drag. Metabolic power is C(i) × weight × v, with v in m/s (km/h ÷ 3.6), weight in kg and C(i) the Minetti energy cost in J/kg/m for gradient i (3.6 on the flat). The tool assumes 25 % mechanical efficiency, so mechanical power is 0.25 times that. Air power is 0.5 × 1.225 × CdA × (v + wind)² × v, with CdA = 0.24 × (weight / 70)^(2/3) m²; wind is in km/h, positive for a headwind and negative for a tailwind. Total is mechanical plus air power, divided by weight for W/kg. The tool also splits out flat power, climbing power (never below zero) and metabolic kcal per hour.

Worked example

70 kg runner at 12 km/h (3.33 m/s) on a 5 % grade into a 10 km/h headwind. Minetti cost at 5 %: 4.69 J/kg/m, so metabolic power is 4.69 × 70 × 3.33 = 1,093 W, and mechanical power is about 273 W. Flat running alone would be 3.6 × 70 × 3.33 × 0.25 = 210 W, so climbing adds about 63 W. Air: relative wind 3.33 + 2.78 = 6.11 m/s, CdA 0.24 m², giving 18.3 W. Total: 292 W, or 4.17 W/kg. Metabolic burn is about 941 kcal per hour.

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Common mistakes

  • Comparing the result with the watts of a wrist or footpod sensor as if they were the same. This is a model estimate from weight, speed and grade, with fixed efficiency and drag assumptions, and sensors use their own algorithms.
  • Entering the headwind as a positive number for a tailwind. A positive value is a headwind and raises power; a tailwind must be negative.
  • Typing the grade as a ratio. A 5 % grade is entered as 5, not 0.05.
  • Using weight with gear or in pounds. The field is body weight in kg, and power scales directly with it.
  • Expecting downhill to show a negative climbing term. The climbing line stops at 0 W, while total power falls because the lower energy cost lowers the mechanical part.

Sources

About this calculator

Running power in watts is modeled as the sum of three physical costs: the power to move your body mass forward on flat ground at your pace, the extra power needed to lift your mass against gravity on any uphill gradient (which is counted as zero on downhills, so the climbing component never goes below 0 W), and the power spent overcoming air resistance, which grows with the cube of your speed relative to the wind and is worsened by a headwind or reduced by a tailwind. Dividing total power by body weight gives watts per kilogram, the metric that lets runners of different sizes compare effort level directly, the same way cyclists do.

Runners who train with power meters — footpods or watch-based sensors — use this kind of breakdown to pace evenly across varying terrain and wind conditions, since power stays a more stable effort signal on hills and in wind than pace or heart rate does. It's also useful without a power meter at all, as a way to sanity-check a sensor's readings or to estimate the power cost of a planned route before running it.

Total power in watts and watts per kilogram, split into the flat, climbing and air-resistance components, is calculated from your weight, running speed, gradient and headwind or tailwind.

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