# Current W/kg used for race category

in Zwiftpower we can see our curent best powers for the specific time.
if i look to my zFTP, it shows 237W. this would give me a 2,9 W/kg.
in ZP i see my W/kg as 3,04.
which one is being used to calculate my current racing category?
thanks

zFTP isnâ€™t based on your 20min power. They shouldnâ€™t have called it something with FTP in the name because it causes confusion.

zFTP is basically Critical Power (CP) and is based on a power curve built from your PBs at various time intervals in the last 90 days.

If you look at your profile on zwift.com you can see the various power PBs which make up your zFTP.

In addition to what Steve said, your weight used to divide your zFTP and zMAP will be an average of the weights at which you set PRs, not simply your current weight. They donâ€™t show you exactly what that is but you can usually get a reasonable idea by doing the math on your PRs.

1 Like

thanks Steve, i think i got it the zFTP vs real FTP.
im wondering if i could use as a reference point, the 95% (or is this a myth?) of mine 20min max power to estimate my FTP.
based on my current values, this would give me exactly the zFTP showed in Zwift.com
if i understood correctly, Zwift will take the best max efforts on the critical curve you mentioned, in the last 90 days right? i think an average wouldt make sense as the numbers would be much lowerâ€¦
cheers

Yes, it uses your best efforts at certain time intervals to calculate the curve and your zFTP. Zwift deliberately donâ€™t give out the formula to try and stop people â€śgamingâ€ť the system. But I think plenty of people have found out that itâ€™s either very close or identical to a CP calculation.

If 95% of your best 20min power is the same as your zFTP then thatâ€™s fine, but it might not stay that way depending on what rides you do. Maybe the types of rides you do will mean that always stays close or the same, but itâ€™s not calculated purely on that basis.

Youâ€™ll find some people claim that zFTP is just x% of y power, but thatâ€™s just a coincidence based on their type of riding.

Very interesting. thanks a lot