Watts per kilo: power to weight ratio explained

4 min read

The cycling world is full of technical terms, but if you’re new to the sport there’s a few you should know. As part of your training, you’ll probably have heard the phrase ‘watts per kilo’ thrown around. But what does it actually mean, and how do you calculate yours?


Simply put, your watts per kilo (w/kg) is your power to weight ratio. Watts per Kilo is your max power output, in watts, divided by your weight in kilos. For example, someone with a weight or mass of 80kg with a sustainable power output of 280 watts will have a power to weight ratio of 3.5 watts per kilo (3.5W/kg).

It’s important because how much you weigh relative to how much power you can generate will determine how well you perform. For everyone who doesn't ride on smooth and flat roads, it’s also important to know the amount of power that can be made in relation to your body weight. Generally the lighter you are, and the greater power generated, the more likely you are to perform better over hills, or wherever gravity may be an issue.


To calculate your power to weight ratio you’ll just need two measurements: your weight in kilograms and your max power output - easily measurable with some scales and a Wattbike!

Make sure you’re correctly warmed up, and then take a 20-minute test, found on the free Wattbike Hub app, and pedal as hard and consistently as you can for the 20 minutes, recording your average power output. Your hour max sustainable output will likely be five to ten per cent lower than this, and your five-minute max sustainable output likely five percent higher. 

Alternatively, you could measure your max amount of power over an FTP test, and then run a seperate five-minute, one-minute and five-second test. Doing it this way will help you to identify your strengths and weakness areas. For example, a high power output over five seconds or a minute indicates sprinting is your strong point, whereas a higher output over five or twenty minutes suggests you may be a stronger climber or time trialist. 


Unless you’re working on a completely flat surface (where success will most likely be dependent on your absolute power), you’ll want to be paying attention to your power to weight ratio. If you’re planning on getting the miles in over a particularly hilly route, or they require explosive sprints, a high power to weight ratio will likely determine your success. 

When you’re riding uphill, you’ll also have to work harder to overcome any aerodynamic resistance. Because of this, your absolute power output will also have some impact, as aerodynamic resistance will rise alongside the rider speed, so don’t overlook its importance. 


In order to improve your watts per kilogram efficiency as a cyclist, you’ll be looking to get the highest max power output for your weight. There are three main ways to do this, these being:

  • Increasing your power output whilst keeping a constant weight
  • Keeping your power output constant whilst losing weight
  • Increasing your power whilst also decreasing weight

It’s worth keeping in mind that if your weight also increases with your max power output, your power to weight ratio may not actually change. This is where factors such as your training routine, strength training and nutrition come into play. Therefore, when you’re training to improve your power to weight ratio, shedding body weight but keeping the same power output is generally more beneficial than staying at the same weight and simply working on your aerobic fitness.
What to do to improve your power to weight ratio

If you’re a beginner, your best bet is to simply get more miles in, indoors on the Wattbike as well as outside. This will improve your aerobic fitness and you’ll lose body fat as you go. If you’re a more experienced cyclist or your fat levels are already quite low, adding more miles may just lead to burnout and subsequent muscle loss. Therefore, targeting max power bursts in your training (through intervals or hill training) can help work on those short power improvements. Remember to work in enough recovery time in between sessions, as this will help the muscles repair and strengthen. Regular weight or strength training can also help prevent loss of power during periods of weight loss, and focusing on your pedalling technique can also help improve your overall cycling efficiency can also help you find those extra watts. 

When you increase your power to weight ratio, your body composition changes. Fat is replaced with lean muscle, which has a number of benefits to your overall health and performance. Added muscle mass helps to improve water retention, meaning you’re less likely to get dehydrated as quickly. Interval, hill and strength training will also help you to improve your VO2 max, which in turn allows you to perform outside of your lactic threshold for longer durations, as increased oxygen efficiency helps the body to buffer lactic acid so you’ll spend less time in an anaerobic state before your next sprint or big push. So, by concentrating on your power to weight ratio, not only will you be building a more efficient body for cycling, but you’ll be building a much healthier and more efficient body overall.


Ready to get started? Why not start your FTP test, or check out these five indoor sessions to improve your cycling performance. 

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