How long will that Zwift climb actually take you?
Put in your weight and the power you can hold, and get a realistic finishing time for Zwift's big climbs - then read why the number comes out where it does. Nothing here is behind a login, nothing is sponsored, and every equation the site uses is written out in the open so you can check it.
Watopia, France, Makuri, London
The same physics applies everywhere. Only the gradient changes.
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Alpe du Zwift, at a glance
Every figure in this table comes straight out of the equation the Alpe du Zwift calculator uses. It is here so you can sanity-check the tool against your own ride without opening it, and so you can see the shape of the curve rather than a single answer.
| W/kg | Estimated time | 70 kg rider | 85 kg rider |
|---|---|---|---|
| 2.0 | 83:36 | 140 W | 170 W |
| 2.5 | 72:53 | 175 W | 213 W |
| 3.0 | 63:25 | 210 W | 255 W |
| 3.2 | 59:58 | 224 W | 272 W |
| 3.5 | 55:11 | 245 W | 298 W |
| 4.0 | 48:11 | 280 W | 340 W |
| 4.5 | 42:26 | 315 W | 383 W |
| 5.0 | 37:54 | 350 W | 425 W |
| 5.5 | 34:38 | 385 W | 468 W |
The highlighted row is the one most people are chasing: roughly 3.2 W/kg is what it takes to get under the hour. Notice how unevenly the time is spread. Going from 2.5 to 3.0 W/kg buys far more than going from 4.5 to 5.0 does, which is exactly why the first year of training feels so much more rewarding than the fifth.
How the estimate is made
There are two honest ways to predict a climb time. You can model the physics from first principles - add up the force of gravity, rolling resistance and air drag, divide the rider's power by the total, and solve for speed. Or you can take a large set of real finishing times, pair each one with the rider's power-to-weight ratio, and fit a curve through them.
The first method is transparent but needs values that Zwift has never published: the exact drag area it assigns your avatar, the rolling resistance of each surface, how it handles rider height. The second method sidesteps all of that, because whatever the game is doing internally is already baked into the times people actually ride. The Alpe du Zwift calculator on this site takes the second route.
The equation, written out
That is the whole model. A 75 kg rider holding 250 W is at 3.33 W/kg. Put that in: 148.60 × 11.09 is about 1,648; 1954.08 × 3.33 is about 6,507; so the estimate is 1,648 − 6,507 + 8,330, which is about 3,471 seconds, or 57:51. You can do that on a phone calculator, which is the point - a model you cannot check is a model you should not trust.
Why the curve bends
On a gradient this steep, almost all of your power is going into lifting your own mass. Air drag barely matters at 10 to 15 km/h. That makes vertical speed close to proportional to power per kilogram, which is why W/kg, and not raw watts, is the number that decides the outcome. A 60 kg rider at 240 W will beat an 85 kg rider at 300 W up the Alpe, despite producing a quarter less power.
The relationship is not a straight line, though, because time is the inverse of speed. Doubling your speed halves your time, so the same absolute gain in W/kg saves progressively less time the faster you already are. The quadratic term is what captures that flattening across the range most riders actually sit in. There is more on the fitting process in the methodology write-up and on the physics in the power-to-weight deep dive.
What it cannot know
The estimate assumes you hold that power steadily for the whole climb. It has no idea whether you went out at 4 W/kg and cracked at hairpin fourteen, whether your trainer is reading 5% high, whether you picked the heaviest bike in your garage, or whether the room is 28 degrees with no fan. Those things are worth more minutes than most riders expect - the article on pacing the Alpe goes through each of them.
One person builds this, and he signs his name to it
Christian Lassen Dam - MSc student in Mechanical Engineering, Aalborg University
I started this site because I wanted to know my own Alpe du Zwift time before I rode it, and the answers I found online were either a shrug or a number with no working shown. So I built the spreadsheet, and then the spreadsheet became a website.
Mechanical engineering is where the physics side comes from - forces, drag and rolling resistance are coursework rather than a hobby. The rest comes from riding: enough hours in Zwift to have earned the Tron bike, and a season of Ironman-distance training that has taught me a lot about what structured work does and does not deliver.
I am not a certified coach and I am not a sports scientist, and I would rather say that plainly than imply otherwise. What I can offer is a clearly explained model, honest limits on it, and a correction the same week if you show me it is wrong.
Latest from the library
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