Turn any finished climb into a VAM number. All you need is the elevation you gained and the time it took.
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This is measured VAM from a climb you've already ridden. To predict VAM from a power target before you ride, use the Hill Climb Calculator.
VAM stands for velocità ascensionale media, Italian for average ascent speed. It is the number of vertical metres you climb per hour, and because it counts height instead of distance, a short steep climb and a long gentle one can be compared on the same scale. It became popular in professional racing as a way to compare mountain performances when power data was scarce.
A rider who climbs 1,150 m in 62 minutes has a VAM of 1113 m/h. Enter your own elevation gain and time above for any climb you have logged.
On a steep climb almost all your effort is lifting mass, so power follows directly from vertical speed. Gravity-only power is total mass × 9.81 × VAM ÷ 3,600. For a 70 kg rider on an 8 kg bike:
| VAM | Gravity power | W/kg (rider) |
|---|---|---|
| 600 m/h | 127 W | 1.82 |
| 800 m/h | 170 W | 2.43 |
| 1000 m/h | 212 W | 3.04 |
| 1200 m/h | 255 W | 3.64 |
| 1400 m/h | 297 W | 4.25 |
| 1600 m/h | 340 W | 4.86 |
| 1800 m/h | 382 W | 5.46 |
Treat those watts as a floor: they include only the gravity term.
To test it, we ride the same 70 kg rider at exactly 4 W/kg up different gradients with the full physics model, read off the VAM, and ask what the shortcut would infer from that VAM alone:
| Gradient | VAM produced | W/kg inferred (true: 4.00) |
|---|---|---|
| 3% | 797 m/h | 2.42 |
| 5% | 1022 m/h | 3.1 |
| 8% | 1152 m/h | 3.5 |
| 12% | 1206 m/h | 3.66 |
The shortcut always undershoots: least on steep climbs and most on gentle ones, where air and tires take a bigger share. That is why a VAM on a 12% ramp says more about power than the same VAM on a 3% drag.
For a more complete answer than the shortcut, divide the climb's length by your time to get average speed, then enter that speed and the gradient into the watts calculator to convert the climb into watts with air drag and rolling resistance included. If you know your power and want the time and VAM it predicts, the hill climb calculator runs the model forward.
On a sustained climb, VAM and power-to-weight move together: a higher W/kg gives a higher VAM. VAM needs no power meter, while W/kg is the sharper number when you have one. Work yours out with the W/kg calculator and compare it with what your climbs suggest.
VAM is steadiest on efforts longer than about five minutes at roughly 5 to 15 percent. Wind, drafting, altitude, heat, road surface and uneven pacing all feed into it, so it records what happened on a specific day rather than a fixed ceiling on your fitness. Compare like with like: similar length, similar gradient, similar conditions.
