How many watts does it take to ride 30 km/h?

On the flat with CdA 0.5 and a rolling coefficient of 0.005, about 208 W for 75 kg of rider and bike; 40 km/h needs about 461 W, because air drag rises with the cube of speed. Enter your own weight and speed and set the grade to 0.

How much does weight matter on a climb?

On a steep climb, almost everything: at 8% and 15 km/h, gravity is about 87% of the power, and every extra kilogram of rider or bike costs about 3.3 W at that speed. On the flat weight barely matters — the aero term dominates.

What is a good watts per kilogram?

It depends on duration. Sustained (about an hour) figures of 2 W/kg are typical for new riders, 3 W/kg for fit club riders, 4+ for strong amateurs and 6+ for professionals. This page gives the W/kg for one speed on one grade, so compare like with like.

How do watts convert to calories?

Watts × seconds ÷ 1,000 is kilojoules at the pedals; because muscles are only about 24% efficient at turning food into pedalling, the kilojoules of work come out nearly equal to the kilocalories burned. 200 W for an hour is 720 kJ of work and roughly 720 kcal.

Cycling Power Calculator (Watts from Speed, Grade and Weight)

Estimated power at the pedals from speed, gradient, rider and bike weight, split into climbing, rolling and aerodynamic drag.

Inputs

Rider + bike mass(kg)

30 kg200 kg

Speed(km/h)

1 km/h80 km/h

Grade(%)

-20 %30 %

Rolling coeff.

0.0020.02

Units

Include CalculateEveryday mark

Estimated power

281 W

Total power

Gravity153.16(54%)
Rolling resistance25.527(9%)
Aero drag102.563(36%)

Working: at 6.94 m/s: gravity 75 × 9.807 × sin(3%) = 22.1 N, rolling 75 × 9.807 × 0.005 = 3.7 N, aero ½ × 1.225 × 0.5 × 6.94² = 14.8 N; power = speed × total force = 281 W
Gravity (climbing): 153 W
Rolling resistance: 26 W
Aero drag (CdA 0.5 m², still air): 103 W
Watts per kg: 3.75 W/kg of rider + bike
Energy per hour: 1012 kJ at the pedals — roughly the same number of kcal burned, at ~24% efficiency

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What each Cycling Power input means

Rider + bike mass: Rider plus bike plus kit, in kg or lb. A 70 kg rider on a 9 kg bike with bottles is about 80 kg.
Speed: Your average road speed, in km/h or mph.
Grade: The road's slope in percent: 0 for flat, 6 for a steady climb, negative for a descent.
Rolling coeff.: The rolling-resistance coefficient. 0.004–0.005 suits good road tyres on smooth tarmac; rough roads and gravel are higher.
Units: Metric (km, kg) or US units (miles, pounds). Mass and speed are converted when you switch, so either set of numbers can be entered.

Cycling Power formula

P = v × (m g sinθ + Cᵣᵣ m g cosθ + ½ ρ CdA v²) · v in m/s, m = rider + bike, θ = atan(grade%), Cᵣᵣ rolling coefficient, CdA = 0.5 m², ρ = 1.225 kg/m³

P = v\left(m g \sin\theta + C_{rr}\, m g \cos\theta + \tfrac{1}{2}\rho\, C_dA\, v^{2}\right)

Riding at a steady speed, the power at the pedals equals speed times the forces holding you back. Three of them matter: gravity on a slope (weight × sin of the angle — every kilogram of rider or bike counts equally), rolling resistance (a small fraction of the weight, set by tyres and road, typically 0.004 to 0.008), and air drag, which grows with the square of the speed and so with the cube of speed in power terms. On a 3% climb at 25 km/h the climb is most of the work; on the flat at 40 km/h the air is. The page splits the watts three ways, gives watts per kilogram — the number climbers compare — and converts to energy per hour. It assumes still air and a typical road-bike CdA of 0.5 m²; a headwind, an upright position or a tailwind moves the aero term a long way.

Cycling Power worked example

75 kg of rider and bike at 25 km/h (6.94 m/s) up a 3% grade with a rolling coefficient of 0.005. Gravity: 75 × 9.807 × sin(1.72°) = 22.1 N; rolling: 75 × 9.807 × 0.005 × cos(1.72°) = 3.7 N; aero: ½ × 1.225 × 0.5 × 6.94² = 14.8 N. Total 40.5 N × 6.94 m/s = 281 W, or 3.75 W/kg — 153 W of it climbing, 102 W pushing air, 26 W on the tyres. On the flat the same speed needs about 128 W.

More Cycling Power examples

80 kg riding at 30 km/h on the flat: rolling takes 33 W and the air 177 W, so about 210 W — five-sixths of it spent pushing air.

85 kg climbing a 6% hill at 15 km/h: gravity alone takes 208 W, and the total is 248 W — slower, yet harder than the flat ride, because now the weight is the cost.

Where the Cycling Power calculator can give the wrong answer

CdA is fixed at 0.5 m², a rider on the hoods. On the drops it is nearer 0.4, in a time-trial tuck 0.25, sitting up on a hybrid 0.6 or more — at 35 km/h that is a difference of 100 W. The aero line is the one to doubt.
Still air is assumed. A 15 km/h headwind at 25 km/h roughly doubles the aero term; a tailwind can make it negative. Real rides average out somewhat but never to zero.
Downhill the gravity term goes negative and can exceed the other two, meaning you would need to brake; the page reports the (negative) total rather than a donut.
Drivetrain loss (2–5%) and the difference between power at the pedals and at the wheel are ignored; a power meter reads a little higher than this for the same speed.
Rolling coefficient: 0.004 for good road tyres on smooth tarmac, 0.006–0.008 for rough roads or touring tyres, 0.01+ for gravel. Doubling it at low speed matters more than it looks.

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Cycling Power reference table

Power on the flat for 80 kg, CdA 0.5 m², still air
Speed	Rolling	Air	Total
20 km/h	22 W	53 W	74 W
25 km/h	27 W	103 W	130 W
30 km/h	33 W	177 W	210 W
35 km/h	38 W	281 W	320 W
40 km/h	44 W	420 W	464 W

Source: Worked out with this page's model (Martin et al. 1998): rolling = m g Crr v with Crr 0.005; air = ½ ρ CdA v³ with ρ 1.225 kg/m³

Cycling Power FAQ

: On the flat with CdA 0.5 and a rolling coefficient of 0.005, about 208 W for 75 kg of rider and bike; 40 km/h needs about 461 W, because air drag rises with the cube of speed. Enter your own weight and speed and set the grade to 0.
: On a steep climb, almost everything: at 8% and 15 km/h, gravity is about 87% of the power, and every extra kilogram of rider or bike costs about 3.3 W at that speed. On the flat weight barely matters — the aero term dominates.
: It depends on duration. Sustained (about an hour) figures of 2 W/kg are typical for new riders, 3 W/kg for fit club riders, 4+ for strong amateurs and 6+ for professionals. This page gives the W/kg for one speed on one grade, so compare like with like.
: Watts × seconds ÷ 1,000 is kilojoules at the pedals; because muscles are only about 24% efficient at turning food into pedalling, the kilojoules of work come out nearly equal to the kilocalories burned. 200 W for an hour is 720 kJ of work and roughly 720 kcal.