Alpe du Zwift Time Calculator
Free forever, no login, no email wall. You give it two numbers — what you weigh and how many watts you reckon you can hold — and it gives you back a time. It will not be kind about it. That is the whole product.
Welcome to the Alpe du Zwift Timing Calculator
This calculator provides you with an estimate of the time it will take for you to complete Alpe du Zwift based upon your weight and intended power target.
Right, so what is w/kg and why does it run the show?
Watts per kilogram. Take the power you're pushing in watts, divide it by what you weigh in kilograms, done. Hold 200 watts at 80 kg and you're at 2.5 w/kg. Hold the exact same 200 watts but you're 70 kg, and suddenly you're at 2.86 w/kg and noticeably faster up the same hill.
That's the whole grubby secret of climbing: gravity does not care how strong you are in absolute terms, it cares how strong you are relative to the weight it has to drag up 1,036 metres. Alpe du Zwift is 12.2 km at an average gradient of 8.5% — peaking around 14% on the nastier of its 21 hairpins — so it's a near-pure test of w/kg. On a pancake-flat route you can bluff with raw watts and a slippery position. Here you cannot. The mountain just weighs you and laughs.
Which is why this calculator asks for weight and power and then quietly ignores both as separate numbers — it only really uses the w/kg that falls out of them. Want a faster time? Two levers: push more watts, or weigh less. (The site is legally obliged to remind you that "weigh less" is doctor-and-dietitian territory, not a watts-saving hack. Don't be daft about it.)
How to actually read the number it spits out
The estimate is a finish time in minutes for the climb at the w/kg you gave it. It is built from the historic times of a whole pile of riders at each power-to-weight, so it's a real-world expectation, not a physics spreadsheet pretending fresh legs and a perfect line. It is the answer to "what do people who ride like me usually clock?" — not "what will you personally do on this exact attempt with that headwind in your sinuses".
It also hands you a second number: the extra watts to lift your odds of actually hitting the estimate up to roughly 90%. Think of the headline time as the coin-flip and that power bump as the insurance premium. Pay it in training and the estimate stops being a hope and starts being a plan.
The median caveat, in plain English (read this bit)
Here's the part everyone skims and then emails me about. The time you get is a median, not a promise. When it tells you 50% of riders at your w/kg went that time or faster, it is also — and people really do struggle with this — telling you that the other 50% were slower. Same number, both halves true. It is the middle of the pack, by definition.
So if you set out chasing that exact figure and miss it by a minute, you haven't failed at maths and the calculator hasn't lied to you — you've just landed in the slower half on the day, which is a coin that lands tails for half of all riders every single time. If you want a time you can bank on rather than gamble on, aim for the w/kg one rung above your target, or take that 90% power bump. That's the difference between an estimate and a guarantee, and gravity charges extra for the guarantee.
The whole range, so you can scout before you suffer
Same maths as the calculator above — same engine, no rounding fudges, no vibes — laid out so you can find your number and see what one more watt per kilo actually buys you.
| Power-to-weight (w/kg) | Estimated time |
|---|---|
| 2.00 w/kg | 90 minutes |
| 2.25 w/kg | 81 minutes |
| 2.50 w/kg | 74 minutes |
| 2.75 w/kg | 68 minutes |
| 3.00 w/kg | 63 minutes |
| 3.25 w/kg | 59 minutes |
| 3.50 w/kg | 55 minutes |
| 3.75 w/kg | 52 minutes |
| 4.00 w/kg | 49 minutes |
| 4.25 w/kg | 46 minutes |
| 4.50 w/kg | 44 minutes |
| 4.75 w/kg | 42 minutes |
| 5.00 w/kg | 40 minutes |
| 5.25 w/kg | 39 minutes |
| 5.50 w/kg | 37 minutes |
| 5.75 w/kg | 36 minutes |
| 6.00 w/kg | 34 minutes |
Yes, the gaps shrink as you go up. The leap from 2.5 to 3.0 w/kg knocks off a proper chunk; the leap from 5.0 to 5.5 barely moves the needle, because by then you're arguing with physics over loose change. That's not a bug, that's the climb being honest with you. Which, around here, is the house style.