PaceCalc

Cycling Power Calculator

How many watts does that speed cost?

Rider Weight (kg)

Bike Weight (kg)

Speed (km/h)

Gradient (%)

Rolling Resistance (Crr)

0.004 racing, 0.008 touringDrag Area (CdA m²)

0.25 aero tuck, 0.4 upright

Power Required

143 W

Watts per kg: 1.91
Rolling: 34 W
Climbing: 0 W
Aerodynamic: 106 W

What you entered

Total mass: 83 kgSpeed: 30 km/hGradient: 0%

1
Convert speed to m/s
30 / 3.6= 8.3333 m/s
2
Rolling resistance power
0.005 x 83 kg x 9.8067 x cos(slope) x 8.3333= 33.9148 W
3
Climbing power
83 kg x 9.8067 x sin(atan(0/100)) x 8.3333= 0 W
4
Aerodynamic drag power
0.5 x 1.225 x 0.3 x 8.3333^3= 106.3368 W
5
Total at the pedals (after drivetrain loss)
(33.9148 + 0 + 106.3368) / (1 - 2/100)= 143.1139 W

Result

Power Required: 143 W

Holding 30 km/h on a 0% gradient takes about 143 W, or 1.91 W/kg.

Power needed by speed and gradient

Total power splits into rolling resistance, climbing against gravity, and aerodynamic drag. Rows use a 70 kg rider on an 8 kg bike, CdA 0.3, Crr 0.005.

Speed	Gradient	Rolling	Climbing	Aero	Total	W/kg
30 km/h	0%	31.9 W	0.0 W	106.3 W	141.0 W	2.01
40 km/h	0%	42.5 W	0.0 W	252.1 W	300.6 W	4.29
20 km/h	5%	21.2 W	212.2 W	31.5 W	270.3 W	3.86
15 km/h	10%	15.9 W	317.1 W	13.3 W	353.4 W	5.05
35 km/h	2%	37.2 W	148.7 W	168.9 W	362.0 W	5.17

Aerodynamic drag rises with the cube of speed: going from 30 to 40 km/h on the flat more than doubles total power, and almost all of the increase is aero. On a 10% climb the picture inverts and gravity accounts for 90% of the effort, which is why position matters on the flat and weight matters uphill.

Drag grows with the cube of speed

Aerodynamic power scales with velocity cubed, so going from 30 to 40 km/h on the flat does not need 33% more power — it needs well over twice as much. This is why aero position and equipment matter enormously at racing speeds and barely at all when climbing slowly.

Why climbing is about watts per kilogram

On a steep gradient almost all your power goes into lifting mass against gravity, and that term scales directly with total weight. Riders are compared by W/kg rather than raw watts because a 60 kg climber at 300 W out-climbs an 85 kg rider at the same output.

Frequently asked questions

I weigh 75 kg and can sustain 200 watts — how fast will I go on flat road?

On flat terrain with no wind, about 30-31 km/h (19 mph) on a road bike in the drops. Roughly 80% of your power goes to fighting aerodynamic drag at that speed.

How is cycling power different from triathlon time?

The cycling power calculator breaks down watts into aero, rolling, and climbing components for a single cycling scenario. The triathlon calculator combines swim, bike, and run times with transitions to project a total finishing time — it's about pacing a multi-discipline race.

What's a good watts-per-kilogram for an amateur cyclist?

For FTP (one-hour sustained power): 2.0-2.5 W/kg is recreational, 3.0-3.5 W/kg is a strong club rider, 4.0-4.5 W/kg is competitive racing, and 5.5+ W/kg is professional Tour-level. Most amateur riders fall in the 2.5-3.5 range.

Why does going from 30 to 35 km/h feel so much harder?

Aerodynamic drag scales with the cube of speed. Going from 30 to 35 km/h (a 17% speed increase) requires about 60% more power to overcome air resistance. The faster you go, the more disproportionate each additional km/h becomes.