Cycling watts per kg.

How the W/kg and climbing estimate work

Watts per kg = power in watts ÷ rider body mass in kilograms. Bike and kit mass are not part of W/kg; they only matter for the climbing estimate.

Climbing speed is the speed at which your power at the wheel equals the sum of three resistances: gravity (m·g·sin θ·v), rolling resistance (m·g·cos θ·Crr·v) and air drag (½·ρ·CdA·v³), where m is rider plus bike mass and θ = atan(grade ÷ 100). The page finds v by bisection. Wheel power = input power × drivetrain efficiency. This is the standard steady-state power-balance model for road cycling (Martin et al., 1998). Still air, constant grade and constant speed are assumed; wind, drafting, acceleration and changes in grade are not modelled.

Worked example

250 W, 70 kg rider, 8 kg bike and kit, 7% grade, Crr 0.005, CdA 0.35 m², air density 1.225 kg/m³, 98% drivetrain efficiency. W/kg = 250 ÷ 70 = 3.57. Solving the power balance gives about 14.5 km/h: roughly 216 W goes to gravity, 15 W to rolling resistance, 14 W to air drag, and 5 W is lost in the drivetrain. That is a climb rate of about 1,014 m/h and about 4:08 per km.

Constants and sources (as of 30 September 2026)

• g = 9.80665 m/s², the standard acceleration of gravity, exact by definition: NIST CODATA.
• Air density 1.225 kg/m³, sea-level standard atmosphere at about 15 °C: NASA Glenn, Earth Atmosphere Model. Real density is lower at altitude and in heat; edit the field.
• Crr, CdA, bike mass and drivetrain efficiency are editable assumptions, not sourced constants. The defaults (0.005, 0.35 m², 8 kg, 98%) are illustrative round numbers for a road rider; tyres, surface and position change them a lot. Measure or look up your own for a tighter estimate.
• Model reference: Martin JC, Milliken DL, Cobb JE, McFadden KL, Coggan AR. Validation of a mathematical model for road cycling power. Journal of Applied Biomechanics 14(3), 1998, 276-291. Journal page.

Category bands

This page deliberately does not label your W/kg as "Cat 3" or "elite". Power-profile tables by Dr. Andrew Coggan are published as downloadable spreadsheets and in the book Training and Racing with a Power Meter, and we could not verify the figures from a public primary page. See Coggan's power profiling article on TrainingPeaks (published 10 October 2008, last updated 8 April 2026) and compare your own number there.

FAQ

Which power should I use?

Use the average power for the climb or effort you care about. Many riders use their threshold power for sustained climbs, but W/kg changes a lot with duration, so compare like with like.

Does bike weight change W/kg?

No. W/kg uses rider body mass only. Bike and kit mass change climbing speed.

Why does the speed differ from my head unit?

Wind, drafting, surging, gradient changes, power-meter calibration and the assumed Crr and CdA all move the result. Treat it as a planning estimate.

Is this coaching or medical advice?

No. It is an arithmetic estimate for pacing and curiosity.

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