# Calculate W/kg on a strava selection made easy

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Calculate VAM (Vetical ascent in meters per hour) and relative power output (W/kg) according to dr Ferrari’s method using a bookmarklet. The relative power output number can be used to compare climbing performance over different sections with different gradients. Do remember that external factors like wind and drag can affect the numbers.

`javascript:var effort=jQuery("#effort-detail").html().split("&nbsp;"),elevation=parseFloat(effort[4].split(" ")[0].replace(",","")),distance=parseFloat(effort[2].split(" ")[0]),duration=effort[8].split(" ")[0].split(":"),hours=duration.length>2?duration[0]:0,minutes=duration.length>2?duration[1]:duration[0],seconds=duration.length>2?duration[2]:duration[1],vam_hours=parseFloat(hours)+parseFloat(minutes)/60+parseFloat(seconds)/3600,drF_climbing_factor=200+elevation/distance,vam=elevation/vam_hours,wkg=vam/drF_climbing_factor;jQuery("#effort-detail").append(" "+vam.toFixed(0)+" m/h "+wkg.toFixed(2)+" W/kg");void 0;`

Give it a name like “dr Ferrari Formula”

Go to a strava activity and select “Analysis”. Select a climbing segment or make your own selection by dragging your mouse over the profile or over the graphs

For example this is a selection based on high power output:

http://www.strava.com/activities/597112546/analysis/4400/5617

Use the bookmark. It should add VAM and W/kg to the selection (right below the altitud graph)

### Now let’s try it out

Kruijswijk preparation for Giro 2016 on Teide. 6.05 W/kg

https://www.strava.com/activities/597112546/analysis/4415/5613

Gesink preparation for Tour de France 2016 on Teide. 6.00 W/kg

https://www.strava.com/activities/597085072/analysis/4117/5318

Kelderman preparation for Tour de France 2016. 6.05 W/kg

https://www.strava.com/activities/597112546/analysis/4413/5616

Warren Barguil preparation for Tour de France 2016 on Sierra Nevada. 5.89 W/kg

https://www.strava.com/activities/599335328/analysis/6482/7329

Kruijswijck 2nd place at Giro 2016 time trial. 6.15 W/kg

https://www.strava.com/activities/584698268/analysis/161/1717

Romain Bardet 6th place at Dauphiné climbing prologue.  6.34 W/kg

https://www.strava.com/activities/599557279/analysis/29/720

Kelderman at tour de Suisse stage 5. 5.74 W/kg

https://www.strava.com/activities/610237398/analysis/11223/13240

When you use your own selection, the device altitude is used. That is less accurate than when you select a segment. With rain the device altitude precision is useless. For example compare this selection:

https://www.strava.com/activities/649954030/analysis/13596/15250

And then compare to the segment by clicking on the corresponding segment.