Key Takeaways
- Enter a distance and a time and you get the steady pedalling power the ride needed. Or enter your power and you get the speed it holds and, with a distance, the time. Both use the Martin power model[1].
- Your CdA and Crr are inputs, not facts the page can know. The tables show what a different CdA or a lighter load would change, so you can see which input matters most.
- For a ride you rode flat out, the page turns a 20-minute or 60-minute average into FTP, and a 5-minute one into a rough VO2max estimate. It gives no FTP for other lengths because I found no sourced factor.
- There is no age-based rating here. Coggan's scale has no age adjustment[5], and the FTP calculator covers what I could verify by age and sex.
How the Calculator Works
One equation, solved in whichever direction you need.
| Result | How it is worked out | Basis |
|---|---|---|
| Power from a ride | Speed is distance over time. Power at the cranks is the sum of air drag, rolling resistance, gravity and bearing friction at that speed, divided by a drivetrain efficiency of 0.97698 | Martin et al. 1998[1] |
| Speed from power | The speed at which that power exactly pays for the same four resistances | Same model, solved the other way[1] |
| Air density | Standard-atmosphere pressure at your elevation and the temperature you enter, treating the air as dry | Standard formulas |
| FTP from an all-out ride | 20-minute power × 0.95, or 60-minute power with no factor | Allen and Coggan[2] |
| Coggan level | FTP in W/kg placed on the functional threshold column of the chart | Coggan power profile[5] |
| VO2max estimate | 10.8 × W/kg + 7, for a maximal ride of about 5 minutes | ACSM leg-cycling equation[7] |
What each result is and where it comes from. Source numbers match the sources list.
Worked example: 40 km in 1:15, 75 kg rider, 8 kg bike
The average speed is 32.0 km/h. With a CdA of 0.30 m², a Crr of 0.0042, flat road and no wind, the ride needed about 165 W at the cranks, or 2.20 W/kg.
Air drag took 129 W of that (78%), rolling resistance 30 W, bearings 1 W and the drivetrain 4 W. Gravity took none because the road is flat.
How Many Watts Does a Speed Cost?
Faster costs more than you would guess, because the power air drag takes grows with the cube of speed.
The table uses the example rider above on flat road in calm air. Change any input in the calculator and the table on the results panel redraws for you.
| Speed | Watts | W/kg | Air drag share |
|---|---|---|---|
| 20 km/h | 52 | 0.70 | 60% |
| 25 km/h | 88 | 1.18 | 70% |
| 30 km/h | 139 | 1.86 | 76% |
| 35 km/h | 209 | 2.78 | 81% |
| 40 km/h | 299 | 3.99 | 84% |
| 45 km/h | 414 | 5.52 | 87% |
Power needed at steady speeds: 75 kg rider, 8 kg bike, CdA 0.30, Crr 0.0042, flat, no wind, 15 °C, sea level. Calculated, not measured.
Going from 30 to 40 km/h is a third more speed and costs 160 W more, which is 114% more power. At 20 km/h air drag is 60% of the total, and at 40 km/h it is 84%.
For a finish time over a whole course with climbs, use the Cycling Race Predictor.
Grade, Wind and Air
The same power gives very different speeds depending on the road.
Take 250 W for the same rider. On flat road in calm air it holds 37.4 km/h. A 10 km/h headwind drops that to 31.5 km/h, and a 10 km/h tailwind lifts it to 44.0 km/h.
Wind does not cancel out over a loop. Martin and colleagues worked through a 40 km out-and-back with their model at 255 W: 60:36 in calm air, against 63:01 with a 4 m/s wind blowing along the course[1]. That is a modelled example, not a measured race.
A 3% grade holds 24.2 km/h at 250 W and a 6% grade holds 15.8 km/h. On the 6% grade the rider climbs about 943 m per hour.
Thinner air at height lowers drag. The 40 km ride in the worked example would need 136 W at 2,000 m instead of 165 W at sea level, which is 28 W less. The tool takes air density from your temperature and elevation, and real pressure and humidity shift it a little.
Choosing CdA and Crr
These two inputs move the answer more than anything else you type.
CdA. It is your drag area, the drag coefficient times your frontal area. A review of wind tunnel work found values for the same time trial position can differ by as much as 40% between studies[11].
So the page offers no position presets. The default of 0.30 m² is a round placeholder, not a typical value.
In the worked example, a CdA 0.05 m² lower would save 22.0 W at the same speed, and 0.05 m² higher would cost 22.0 W. If you can, measure your own with the Cycling CdA Calculator.
Crr. The default of 0.0042 is the middle road tire in Bicycle Rolling Resistance's drum tests, with the fastest tenth near 0.0029 and the slowest tenth near 0.0057[10].
That drum is covered in diamond plate to mimic an average road, and it tests one tire at 28.8 km/h under a 42.5 kg load. A drum misses the vibration losses on rougher surfaces[12], so rough roads usually cost more. The Cycling Rolling Resistance Calculator shows how to read that table.
Weight. One kilogram less, on the rider or the bike, saves 0.4 W at the same speed on the flat. On a climb the saving is bigger, because gravity depends on mass.
Using an All-Out Effort: FTP, Level and VO2max
These lines appear only when you mark the ride as all-out, and only for lengths I could source.
FTP. Allen and Coggan take FTP as 95% of the average power from a 20-minute test[2]. In one study, 17 of 19 highly trained athletes finished 60 minutes at 95% of their 20-minute power[3].
A study of 120 cyclists, grouped by their VO2max, fitted a factor from 20-minute to 60-minute power: 0.88 for recreationally trained riders, 0.92 for trained, 0.95 for well trained and 0.96 for professionals[4]. So 0.95 fits well-trained riders best, and your real FTP may be lower.
A true 60-minute effort needs no factor, because FTP is defined as the power you can hold for about an hour[2]. For any other length I found no sourced factor, so the page shows your W/kg and no FTP.
Worked example: 11.5 km in 20 minutes, same rider
That is 34.5 km/h and about 201 W, so the FTP estimate is 191 W, or 2.55 W/kg. On the men's column of Coggan's chart that is "Fair".
A 60-minute ride of 33 km needs 179 W and gives an FTP of 179 W with no factor.
The windows. The page treats a ride within 2 minutes of 20 minutes, within 5 minutes of 60 minutes, and within 1 minute of 5 minutes as that length. Those limits are my own choice, not published rules.
Coggan level. Coggan built the chart by anchoring world champions at the top and untrained people at the bottom, from young adults[5]. For functional threshold that is 6.60 and 2.22 W/kg for men, and 5.69 and 1.83 W/kg for women.
It has no age adjustment and is not a survey of riders. For what I could verify by age and sex, see the FTP by age and gender section of the FTP calculator.
VO2max. ACSM's leg-cycling equation is VO2 = 1.8 × work rate in kgm/min ÷ body mass + 7, which is 10.8 × W/kg + 7[7]. The sources I read convert 1 W to 6 kgm/min[8]. The exact figure is 6.118, which would lift the W/kg part of the result by about 2%.
A coach's worked example on the Hunter Allen Power Blog, 300 W at 75.9 kg, gives 49.7 mL/kg/min. It applies the equation to 20-minute power[9].
I use it only for a maximal ride of about 5 minutes, since Coggan describes VO2max intervals as 3 to 8 minutes[6]. He also notes that most athletes can hold, for 5 minutes, a power that would elicit 105 to 110% of their VO2max[5], so the estimate may read high.
The equation was written for 50 to 200 W[8], so a strong rider's 5-minute power is an extrapolation and the page says so. I found no error figure I could trace to a study, so it shows none.
How Accurate Is It?
Good physics, uncertain inputs.
Martin and colleagues' equation matched a power meter to a standard error of 2.7 W over their road trials, with drag area, air density and wind measured[1]. Yours will not be that clean. I have not tested this tool against a power meter or against wind tunnel results.
Those trials were 38 rides at 7 to 12 m/s (25 to 43 km/h) over a 472 m section with a 0.3% grade[1]. Slower speeds, steep climbs and long descents go beyond what they tested.
In the worked example, a CdA error of 0.05 m² moves the answer by about 22 W. Read the result as a range around your CdA, not a single point.
The ride direction assumes one steady speed. Ride 20 km at 20 km/h and then 20 km at 40 km/h and you finish 40 km in 1:30:00, the same as riding steady at 26.7 km/h.
The steady ride needs 104 W. The two-speed ride averages 135 W over the same 1:30:00, because the fast half costs more than the slow half saves.
In real rides, stops, surges, braking and wind changes push the true power up for the same average speed. Use moving time on a steady stretch for the best match.
What It Cannot Tell You
Worth knowing before you plan around the numbers.
- It is not a power meter. The power from a ride is a model result, and it is only as good as your CdA, Crr, weight and wind.
- No drafting. It assumes you ride alone. A review reports 15 to 50% less drag directly behind another rider and 10 to 30% about a bike length back[11], so a group ride needs less power than the tool says.
- No age or percentile ratings. I left out performance levels by age, percentiles, time standards and training speeds because I could not trace them to a source.
- No race prediction from one ride. Scaling one result to other distances needs a fatigue model I could not source. For a modelled finish time on a course, use the Cycling Race Predictor.
- No normalized power, IF or TSS. Those need second-by-second power from a ride file. The Cycling NP, IF and TSS Calculator works from that.
Frequently Asked Questions
Sources & References
- Validation of a Mathematical Model for Road Cycling Power. Martin JC, Milliken DL, Cobb JE, McFadden KL, Coggan AR. Journal of Applied Biomechanics 14(3):276-291 (1998)
- Training and Racing with a Power Meter, 2nd ed.. Allen H, Coggan AR. VeloPress (book) (2010)
- Is the FTP test a reliable, reproducible and functional assessment tool in highly-trained athletes?. McGrath E, Mahony N, Fleming N, Donne B. International Journal of Exercise Science 12(4):1334-1345 (2019)
- An update of the Allen & Coggan equation to predict 60-min power output in cyclists of different performance levels. Sitko S, Cirer-Sastre R, López-Laval I. International Journal of Sports Medicine 44(13):983-987 (2023)
- Creating your power profile. Coggan A (TrainingPeaks). trainingpeaks.com, published 10 October 2008, updated 8 April 2026
- Cycling power zones explained: Coggan's 7-level system. Coggan A (TrainingPeaks). trainingpeaks.com
- Metabolic calculations cases (ACSM Guidelines, 11th ed., Table D.1, written out as equations). Bushman BA. ACSM's Health & Fitness Journal 27(2):6-10 (2023)
- How to calculate calories expended (quoted for the 300 to 1,200 kgm/min range; secondary source). IDEA Health & Fitness Association. ideafit.com
- How to calculate your own VO2max (ACSM equation applied to 20-minute power). Myers C (Peaks Coaching Group). Hunter Allen Power Blog, 24 June 2013 (2013)
- Road Bike Tires Test Results (table read 3 November 2026). Bicycle Rolling Resistance. bicyclerollingresistance.com
- Riding against the wind: a review of competition cycling aerodynamics. Crouch TN, Burton D, LaBry ZA, Blair KB. Sports Engineering 20:81-110 (2017)
- Are bicycle tyre tests lying to you? Rethinking rolling resistance and drum testing (secondary source, quotes Josh Poertner of Silca). Cycling Weekly. cyclingweekly.com
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Disclaimer: This calculator is for informational and personal journaling purposes only. It logs measurements and compares them to published reference values. It is not health, medical, or nutrition advice.