Normalized Power, IF and VI Calculator

Average power tells you almost nothing about how a ride felt. A flat steady hour and a crit full of accelerations can post the same average and tax your body completely differently. Normalized Power, Intensity Factor and Variability Index pull those rides apart. The calculator above takes the numbers off your head unit and returns the ratios that tell you how hard the effort was and how evenly you spread it.

What the numbers are

Your head unit already computes Normalized Power from the power stream. NP weights the hard surges more than the easy spinning, so it tracks the physiological cost of a ride better than a plain average. This tool takes NP and turns it into two ratios.

• Normalized Power (NP): read it straight off the head unit after the ride.
• Average Power (AP): the plain mean watts for the same ride.
• FTP: your current threshold power, the anchor for everything.
• Ride duration (optional): add it and you also get TSS.

IF is NP divided by FTP. VI is NP divided by AP. Both fall out in a second.

Reading the result

IF tells you how hard the ride was relative to threshold. An IF of 0.70 is an endurance ride. Around 0.85 to 0.95 is threshold and tempo work. Push past 1.0 and you held more than your hour power, which only happens on short hard efforts or a sandbagged FTP.

VI tells you how the watts were distributed. A VI near 1.0 means you held steady power, a time trial or a turbo session. Climb toward 1.1 and the ride was punchy: group surges, repeated climbs, a stochastic crit. High VI at low IF often means a chaotic group ride that cost more than the IF alone suggests.

If you entered duration, TSS scales both intensity and time, so a two-hour endurance ride and a one-hour threshold ride can land at the same training load.

The common mistake

All of this rests on FTP being honest. A number you set three months ago and have outgrown inflates every IF reading, and a sandbagged test does the opposite. Retest before you trust a block of these ratios. And do not read VI on a 20-minute solo effort. It needs terrain and traffic to mean anything.

For how power, NP and intensity tie together across a whole ride, read the full normalized power guide.