How to use the calculator
- Pick a climb or enter its numbers. If the climb is in our climbs database, pick it and we’ll load its distance, elevation gain, altitude and profile. If not, enter the distance and elevation gain, or the average grade if that’s what you know.
- Enter your weight, the bike’s weight and your gear’s (bottles, clothing, shoes). On a climb, every pound counts.
- Choose how to calculate:
- From my watts: the average power you think you can hold for the whole climb.
- From my W/kg: if you think in watts per kilogram, like the leaderboards do.
- For a target time: enter the time you want to hit and we’ll tell you the power you need.
- Adjust position and average altitude if you want. On a climb, position matters little; altitude matters a bit more on climbs topping out above 6,562 ft (2,000 m).
Below the result there’s a table with the times for 2, 2.5, 3, 3.5, 4 and 5 W/kg, at your weight, on the same climb. The highlighted row is the one closest to your level.
How we calculate it
We use the same physics model as the power to speed calculator, the one by Martin and colleagues (1998):
P = [ ½ · ρ · CdA · v³ + Crr · m · g · cos θ · v + m · g · sin θ · v ] ÷ (1 − losses)
For each section we find the speed v at which your power P equals the sum of the resistances: air (with the density ρ at the average altitude), rolling resistance on average pavement (Crr = 0.0045) and, above all, gravity (m · g · sin θ · v), which on a climb takes 85-90% of your watts. We assume 59 °F (15 °C), no wind and 2.5% drivetrain losses.
We add up the time for each section. If the climb has a section-by-section profile, we calculate it that way; if not, we use the average grade. Then we get:
- Average speed = distance ÷ time.
- VAM = elevation gain ÷ time, in meters per hour (the unit cyclists use worldwide, even in the US).
- W/kg = watts ÷ your body weight (without the bike).
For the reverse mode we try different power levels until we find the one that gets you up the climb right on your target time.
Climb times by W/kg
A 165 lb (75 kg) rider on an 18 lb (8 kg) bike with 3.3 lb (1.5 kg) of gear, hands on the hoods, average altitude of 3,281 ft (1,000 m). VAM in m/h in parentheses.
| W/kg | 3.1 mi (5 km) at 6%, 984 ft | 6.2 mi (10 km) at 7%, 2,297 ft | 9.3 mi (15 km) at 8%, 3,937 ft | 12.4 mi (20 km) at 6%, 3,937 ft |
|---|---|---|---|---|
| 2.0 | 31 min (578) | 1 h 11 min (589) | 2 h 01 min (597) | 2 h 05 min (578) |
| 2.5 | 25 min (714) | 58 min (730) | 1 h 37 min (742) | 1 h 41 min (714) |
| 3.0 | 21 min (845) | 48 min (868) | 1 h 21 min (884) | 1 h 25 min (845) |
| 3.5 | 19 min (970) | 42 min (1,001) | 1 h 10 min (1,023) | 1 h 14 min (970) |
| 4.0 | 17 min (1,091) | 37 min (1,131) | 1 h 02 min (1,159) | 1 h 06 min (1,091) |
| 5.0 | 14 min (1,316) | 31 min (1,377) | 51 min (1,420) | 55 min (1,316) |
The elevation gains are 300, 700, 1,200 and 1,200 m. Two useful takeaways:
- VAM depends on the grade. At the same W/kg, VAM goes up the steeper the climb, because less energy is lost to the air. That’s why you shouldn’t compare VAM across very different climbs.
- W/kg rules, but not completely. At the same 3 W/kg, a 132 lb (60 kg) rider takes about 50 minutes on the 6.2-mile climb at 7% and a 209 lb (95 kg) rider about 47, because the bike weighs proportionally more for the lighter rider.
To see what level your W/kg puts you at, use the watts per kg calculator. Times already worked out for Alpe d’Huez, the Angliru, the Tourmalet and other famous European climbs are in the climb times by W/kg chart.
Weight or watts: what pays off more
On the 6.2-mile (10 km) climb at 7% at 225 W (about 48 minutes):
| Change | Time saved |
|---|---|
| 2.2 lb (1 kg) lighter bike | 31 s |
| 4.4 lb (2 kg) less body weight | 1 min 02 s |
| 10 W more | 1 min 56 s |
| Hands in the drops instead of on the tops | 27 s |
The rule of thumb: on a climb, losing 1% of total mass is worth almost the same as gaining 1% of power. But there’s a healthy limit to how much weight you can lose, and no such limit on gaining watts through training.
Common mistakes
- Using the power from a short test. If your best 5-minute power is 300 W, you won’t hold it for 50 minutes. For a climb longer than 20 minutes, start from your FTP. If you don’t know it, work it out with the FTP calculator.
- Forgetting you’ll start the climb tired. If you hit it with 62 miles (100 km) in your legs, you’ll produce 5-10% less than in a test.
- Trusting the average grade on an irregular climb. A climb with 12% ramps and 3% recovery sections is a bit slower than a steady one with the same average, and it calls for lower gears. Check yours with the gear ratio calculator.
- Comparing with a Strava time set in a group or with a tailwind. The model assumes you climb alone with no wind. A good tailwind on a gentle climb can hand you several minutes.
How accurate it is
With real power data, the model is typically within ±3-5% on steady climbs. The biggest sources of error are wind, road surface, switchbacks (where the inside line is much steeper) and, above all, how hard it is to hold perfectly steady power.
Frequently asked questions
How long does it take to ride up a 6-mile climb at 7%?
For a 165 lb (75 kg) rider on an 18 lb (8 kg) bike, a 6.2-mile (10 km) climb at 7% takes about 57 minutes at 2.5 W/kg, 48 minutes at 3 W/kg and 37 minutes at 4 W/kg. A lightly trained rider at 2 W/kg will need about an hour and ten minutes.
What is VAM in cycling?
It's vertical ascent speed (from the Italian velocità ascensionale media): the meters of elevation you gain in an hour. A fit amateur climbs at 800-1,000 m/h (2,625-3,281 ft/h); the best pros top 1,700 m/h (5,577 ft/h) on long climbs.
Which saves more time on a climb, losing weight or gaining watts?
On a 6.2-mile (10 km) climb at 7%, 4.4 lb (2 kg) less saves just over 1 minute and 10 W more saves almost 2 minutes. Gaining 4% more power is worth the same as losing 4% of total weight (rider plus bike).
What power should I use to estimate a long climb?
For climbs of 20 to 60 minutes, a power close to your FTP (what you can hold for an hour), between 95 and 105%. For climbs over an hour, 85 to 95% of FTP if you want to reach the top in one piece.
Why does an irregular climb take longer than a steady one with the same average grade?
Because you go slower on the steep sections and spend more time on them. At 225 W, 3.1 miles (5 km) at 4% followed by 3.1 miles at 10% takes about 49 minutes, versus 48 for a steady 7% climb.