Power-to-Weight Ratio: What’s Watts per Kilogram All About?

By Hunter Allen, Coach and Power Training Expert at Peaks Coaching Group

You hear so many cyclists talking about their watts per kilogram ratios: is it really that important? Why is there so much emphasis on the power-to-weight ratio metric in cycling? Will the person with the best watts per kilogram (w/kg) always win in a mountain stage? What about sprinting? Or a mountain bike race? Below I’ll be digging into some of these frequently asked training questions.

Ask any cyclist if a lighter bike is better than a heavier bike and they will respond with an emphatic, “YES!” Why is that? Simply, it takes less energy to pedal a lighter bicycle faster up a hill, into a head wind and I would even argue on a dead flat road in most cases.

After all, cycling is a sport of energy conservation and that’s one of the reasons our races, in most cases, are so darn long. It’s only after a hundred miles or more that the riders become fatigued and then are able to distinguish themselves as the rider that is not only the strongest, but the one that conserved the most energy. Of course, throw in a mountain, 30 rolling hills, a crosswind and some corners and you have even more variables that can make a difference in the outcome of a cycling event.

What is Watts per Kilogram?

Watts per kilogram, or w/kg, is a basic power- to-weight ratio measurement. This data point reflects how many watts can you hold for a certain period of time, divided by your weight in kilograms - and can help you to compare your fitness level with others.

What is your weight in kilograms? If you are used to measuring your weight in pounds (lb.), then take your weight in pounds and divide by 2.2- and that will be your weight in kilograms. Then take your average power for a 60-minute all-out effort and divide that by your weight in kilograms. This result is your watts per kilogram ratio.

Let’s put this math to work in an example. Let’s say Joe Athlete weighs 165 lb and can hold 270 watts for an hour. 165 divided by 2.2 equals 75 kg, and 270 watts divided by 75 kg is 3.6 w/kg.

Maybe you have wondered why your friend who weighs 20 pounds more can put out so many more watts than you, yet you’re always side-by-side on any climb? In general, people that are heavier and fit have bigger muscles, which usually means they can create more force on the pedals, thereby producing more absolute watts when riding. However, because they weigh more, the additional watts that they produce is cancelled out by their additional weight.

In this case, both your and your friend’s power-to-weight ratios are so close to each other, and as long as aerodynamics don’t come into play, you both will be close to each other on a climb.

So, is power-to-weight “the end all, be all” in deciding success in cycling? Definitely not. Cycling has many aspects to it with tactics by individuals and teams, bike handling skills, energy conservation, mental strength and desire, nutritional needs and more that shape every bike race and determine the winner.

If w/kg ratio was the only thing that determined winners, then we could all just show up at a race and show our “certified” test results and the highest one would be declared the winner without actually having to race each other. Thankfully, that’s not the case for those of us that love racing!

There have been many talented racers with sky high w/kg ratios that haven’t ever won a race. And there are many that have relatively low w/kg ratios for their category yet dominate with win after win during the season. For certain your w/kg is important, and when climbing a steady climb over a mile long watts per kilogram does have a lot to do with determining success, as the rider with the highest w/kg ratio will most likely be the first rider to the top.

The Power Profile

It’s been a while now, but back in 2003, Dr. Coggan and I put together a chart that we called the Power Profile (see Figure 1). In the early days of power training, we often wondered how we and other riders stacked up against the world’s best. We set out to capture power files from the world’s best riders when they created a World Championship winning performance and used these numbers to anchor the “tippy top” of the Power Profile.

We then extrapolated down from there to recreational and novice cyclists establishing ranges of w/kg ratios for each racing category. Once that was done, we acquired and analyzed over 300 different riders’ “bests” to see where they would fit into the Power Profile to confirm its accuracy.

For example, a category 3 racer with a “world class” sprint could have an incredibly high 5-second w/kg ratio but be just “good” with their 60-minute or FTP power – which was why they were only a category 3 racer. With further tweaking and the acquisition of more power files, we found that not only was the Power Profile a great way to compare oneself against others, but to learn your strengths and weaknesses.

Figure 1: The Power Profile

One rider might have a great w/kg ratio for their 5-minute power, but couldn’t sustain that power for 60 minutes and therefore needs to improve their FTP in order to stay with the top riders in their category. This is one example of how understanding your strengths and weaknesses by using the Power Profile is really one of the best uses of looking at your w/kg ratios.

To understand this, you will need to do some testing and achieve the best numbers you can possibly achieve during your testing. You will need to test your best 5-seconds , 1- minute, 5-minutes and 60-minutes.

Why do you have to test different durations? Well, each duration represents a different energy system in your body. Neuromuscular power, or the ability to quick contract and relax your muscles, is represented in a 5-second sprint; whereas your ability to produce energy without oxygen, called your Anaerobic Capacity, is represented by your 1-minute power; and Vo2max, or the size of your lungs and ability to process that oxygen, is represented by your 5-minute power.

Your aerobic engine, or ability to sustain a high level of power without fatiguing for roughly an hour, is your 60-minute power or FTP (Functional Threshold Power). Below I lay out how to test for your Power Profile over a 2-day period.

Figure 2: Power Profile Testing Protocols, Day 1

Figure 3: Power Profile Testing Protocol, Day 2

After you have completed the Power Profile testing, then convert your results into w/kg for each of the different durations and plot your Power Profile. This is an easy way to discover and begin to understand your strengths and weaknesses, as well as how it compares to your race or ride demands and goals.

Do you need to improve in one or more of the columns? For a more in-depth discussion of the Power Profile, be sure to pick up a copy of a book by Dr. Coggin and myself, “Training and Racing with a Power Meter”. (Pro Tip: Autographed copies can be purchased right on my website!)

In conclusion, while your power-to-weight ratio is important, and you want to have the highest w/kg ratio possible, it does NOT guarantee success.

There are so many factors involved in cycling success (and we haven’t even discussed aerodynamics!), your w/kg ratio is just one of these. It’s important that you continually improve your handling skills, racing tactics, nutrition protocols and energy conservation in order to increase your chances in achieving your next goal.