This article was first posted on April 30, 2024

Notice the two areas in yellow. One is titled “Weighted Avg Power” and the other is “Power.”

What’s the difference?

Here is a screenshot from Strava of a club rider’s results.

The three most popular bike computers (Garmin, Wahoo and Bryton) use the same methods of determining the power you put into each ride, and they offer the same options. If you have a power sensor on your bike,

Your computer records your power once each second, measured in watts. Weighted Avg Power and Power are both based upon a 30-second period derived from these one-second recordings. So twice a minute, records are made of your power output, each record having 30 items in it. If you don’t have a power meter connected to your computer, Strava estimates it.

*NOTE: If math is not your thing, just go to the last two paragraphs of this article.

Here’s how the Power metric works:

Let’s say you just rode a 1.5 hour route.
1.5 hours = 90 minutes
90 minutes = 180 unique 30-second recordings
Let’s say the average of those 180 unique 30-second recordings was 90 watts
90 watts is your Power number, meaning your average power output during the entire ride was 90 watts. That includes coasting/stopping/pedaling.

At first glance, this seems to be the best way to determine the average power you put out on this ride, but you’d be right and wrong. It is the mathematical average of your coasting/stopping/pedaling power. Your computer adds up all the 30-second segments and then divides that by 180. It is the true average power.

However, for training purposes, it’s more important to know ***how much power*** you were putting out ***only while pedaling*** instead of adding in the coasting/stopping metrics, over which you may have no control (stop lights, traffic, your position in the group, etc.).

To provide a more meaningful number for the power you output on your ride, the cycling industry has agreed upon a method of emphasizing when you’re pedaling, and at how many watts, as opposed to giving equal importance to when you’re coasting/stopping and putting out zero watts. This is the Weighted Avg Power, sometimes called “Normalized Power.” It was originally developed by [Andrew Coggan Ph.D.](https://shhs.iupui.edu/connect/directory/coggan-andrew.html) , an associate professor in the Department of Kinesiology at the Indiana University School of Health & Human Sciences.

Here’s how the Weighted Avg Power works:

Let’s say you just rode a 1.5 hour route.
Your computer takes each 1-second segment and raises it to the 4th power (multiplies it by itself 3 times). This means when you’re coasting (0 watts), 0 x 0 x 0 x 0 = 0 watts. If when you’re pedaling you’re putting out 130 watts, that becomes 130 x 130 x 130 x 130 = 285,610,000 watts, computed to the 4th power. It then adds up each second’s computed number for 30 seconds and determines the mathematical average.
Let’s say you coasted for 15 seconds and pedaled at 130 watts for 15 seconds. That would compute to (15 x 0) + (15 x 285,610,000) = 0 + 4,284,150,000 = 4,284,150,000 watts, computed to the 4th power. Divide that by 30 seconds and you have an average of 142,805,000 watts, computed to the 4th power.
Your computer then takes that average and computes the 4th root of 142,805,000 watts, which equals 109.32 watts, becoming that 30-second segment’s Weighted Avg Power.
The mathematical average of those 180 unique 30-second recordings then becomes the Weighted Avg Power for your entire ride.

Notice that the Weighted Avg Power is greater than the Power number. This is because the formula emphasizes the watts you’re outputting while pedaling and minimizes the 0 watts while coasting/stopping.

In the screenshot above, you can see that the Weighted Avg Power was 118 watts, whereas when coasting/stopping info was combined into the true mathematical average, the average was only 98 watts. For training purposes, the 118-watt number is more meaningful because it indicates the average power while pedaling. Comparing the Power and Weighted Avg Power metrics is useful, but cycling trainers consider Weighted Avg Power as crucial for training because it better reflects the exertion and impact of the more intense portions of a ride that typically influence fitness gains and performance adaptations more significantly than steady or low power outputs.

Now you know the difference between, and the purposes of, Weighted Avg Power and Power on your Strava page.

Questions? Just ask!
Dick Brock, stats@bikeirvine.org