These numbers come from the power model by Martin and colleagues (1998): the power at the pedals is what the air takes, plus what tire rolling resistance takes, plus 2.5% lost in the drivetrain. It’s the same math as our power and speed calculator, where you can change the weight, wind, grade or altitude. We ran it at whole miles per hour; the kilometers per hour are alongside.
Watts needed by speed
On flat ground, no wind, at sea level and 68 °F (20 °C). Average power at the pedals, in watts.
| Speed | Road, hoods | Road, drops | Aero bars | Gravel or MTB on pavement | Gravel or MTB on hardpack | Gravel or MTB on loose dirt |
|---|---|---|---|---|---|---|
| 12 mph (19.3 km/h) | 52 W | 49 W | 44 W | 67 W | 83 W | 102 W |
| 13 mph (20.9 km/h) | 62 W | 58 W | 52 W | 81 W | 99 W | 119 W |
| 14 mph (22.5 km/h) | 73 W | 69 W | 61 W | 97 W | 116 W | 138 W |
| 15 mph (24.1 km/h) | 87 W | 81 W | 72 W | 116 W | 136 W | 160 W |
| 16 mph (25.7 km/h) | 101 W | 95 W | 83 W | 137 W | 159 W | 184 W |
| 17 mph (27.4 km/h) | 118 W | 110 W | 96 W | 160 W | 183 W | 210 W |
| 18 mph (29.0 km/h) | 136 W | 127 W | 111 W | 186 W | 211 W | 239 W |
| 19 mph (30.6 km/h) | 157 W | 145 W | 127 W | 215 W | 241 W | 271 W |
| 20 mph (32.2 km/h) | 179 W | 166 W | 144 W | 247 W | 274 W | 306 W |
| 21 mph (33.8 km/h) | 204 W | 189 W | 163 W | 282 W | 311 W | 344 W |
| 22 mph (35.4 km/h) | 231 W | 213 W | 184 W | 321 W | 351 W | 385 W |
| 23 mph (37.0 km/h) | 260 W | 240 W | 206 W | 363 W | 394 W | 430 W |
| 24 mph (38.6 km/h) | 292 W | 269 W | 231 W | 408 W | 441 W | 479 W |
| 25 mph (40.2 km/h) | 326 W | 301 W | 257 W | 458 W | 492 W | 531 W |
| 26 mph (41.8 km/h) | 364 W | 335 W | 286 W | 511 W | 547 W | 587 W |
| 27 mph (43.5 km/h) | 404 W | 371 W | 317 W | 569 W | 606 W | 648 W |
| 28 mph (45.1 km/h) | 447 W | 410 W | 350 W | 631 W | 669 W | 713 W |
Assumptions behind each column
| Column | Total weight | CdA | Crr | Share taken by the air at 18 mph |
|---|---|---|---|---|
| Road, hoods | 183 lb (83 kg) | 0.33 m² | 0.0045 | 78% |
| Road, drops | 183 lb (83 kg) | 0.30 m² | 0.0045 | 76% |
| Aero bars | 183 lb (83 kg) | 0.25 m² | 0.0045 | 73% |
| Gravel or MTB on pavement | 192 lb (87 kg) | 0.48 m² | 0.0045 | 83% |
| Gravel or MTB on hardpack | 192 lb (87 kg) | 0.48 m² | 0.008 | 73% |
| Gravel or MTB on loose dirt | 192 lb (87 kg) | 0.48 m² | 0.012 | 65% |
Total weight is a 165 lb (75 kg) rider plus 18 lb (8 kg) of bike and gear on the road, and 26 lb (12 kg) on a gravel or mountain bike. CdA is your frontal area times your drag coefficient: how much air you push. Crr is the rolling resistance coefficient: how much the tire drags on the ground. They’re typical values from the research literature and wind tunnel testing; yours can vary by 10-15% with your size, clothing and tires.
Weight barely matters on the flat
Road bike, hands on the hoods, at different total weights (rider, bike and gear).
| Total weight | 15 mph (24 km/h) | 18 mph (29 km/h) | 20 mph (32 km/h) | 22 mph (35 km/h) | 25 mph (40 km/h) |
|---|---|---|---|---|---|
| 140 lb (64 kg) | 81 W | 129 W | 171 W | 222 W | 317 W |
| 160 lb (73 kg) | 83 W | 133 W | 175 W | 226 W | 321 W |
| 180 lb (82 kg) | 86 W | 136 W | 179 W | 230 W | 326 W |
| 200 lb (91 kg) | 89 W | 139 W | 182 W | 234 W | 330 W |
| 220 lb (100 kg) | 92 W | 143 W | 186 W | 238 W | 335 W |
| 240 lb (109 kg) | 94 W | 146 W | 190 W | 242 W | 340 W |
How to read the chart
- The power the air takes grows with the cube of your speed. That’s why going from 18 to 25 mph costs more than twice the watts, and from 25 to 28 mph almost 40% more.
- Wind changes everything. With a 6 mph (10 km/h) headwind, holding 18 mph on the hoods takes 219 W instead of 136 W; with the same wind at your back, 77 W.
- Drafting saves a lot, because the rider in front breaks the wind for you. The chart is for whoever is pulling or riding alone.
- On gravel, tires and pressure rule on dirt. A wide tire at the right pressure rolls faster on dirt than a narrow, hard one; find yours with the tire pressure calculator.
If what you want to know is how long a climb would take you, check the climb times by W/kg chart. If you’re torn between two bikes, the gravel vs. road bike guide compares them. And to plan the pace of a long ride, the guide to your first century ride uses this same model to work out how long you’ll take at your watts.
Frequently asked questions
How many watts does it take to ride 20 mph on flat ground?
About 179 W on a road bike with your hands on the hoods, 166 W in the drops and 144 W on aero bars. On a gravel or mountain bike with your hands up top, it's about 247 W on pavement and 274 W on hardpacked dirt.
How many watts is 25 mph on a bike?
About 326 W on a road bike on the hoods, with no wind and no wheel to follow. In the drops it falls to 301 W and on aero bars to 257 W: position matters more than the bike.
Does weight matter on flat roads?
Not much. Going from 140 to 240 lb (64 to 109 kg) of total weight only raises the power at 18 mph (29 km/h) from 129 to 146 W on a road bike. On the flat the air rules, taking about three quarters of your watts.