Power to weight calculator

Watts per kilo decides who gets up the hill first. Here is yours, what band it sits in, and what one kilogram is actually worth on a climb.

## Why the ratio matters more than the watts

On the flat, raw watts win. Air resistance does not care what you weigh, so a big rider making 300 watts goes faster than a small one making 250, and that is the end of it.

On a climb the question changes completely. Lifting mass against gravity takes power in direct proportion to the mass, so what matters is how many watts you have per kilogram you have to carry up. This is why climbers are small and sprinters are not, and why a 60 kg rider with an FTP of 240 will ride away from an 80 kg rider with an FTP of 300 the moment the road tilts.

The crossover is roughly where gravity starts to dominate air, which on a road bike is somewhere around three or four per cent.

## What the bands actually mean

The table is a rough map, not a rulebook. Treat the boundaries as fuzzy by at least a couple of tenths, because:

• FTP tests disagree with each other. A ramp test and a twenty-minute test on the same rider in the same week can differ by five per cent, which moves your W/kg by a fifth of a band.
• Indoor and outdoor figures differ. Most riders test lower indoors. If you are comparing your trainer number with someone's outdoor number you are not comparing like with like.
• Duration is everything. W/kg at threshold is one thing; W/kg for five minutes, or for twenty seconds, is a different and often very different number. A sprinter can look ordinary at threshold and terrifying for thirty seconds.

What the bands are genuinely useful for is tracking yourself over seasons and working out whether a given group ride is going to be enjoyable or humiliating.

## The honest version of "just lose weight"

You will see the advice everywhere, and the arithmetic does work: at a fixed FTP, dropping a kilogram raises your W/kg. The calculator shows what a kilo is worth on your chosen gradient, and on a steep climb it is not nothing.

But two things are usually left out.

Weight and power are not independent. Riding on less fuel than you need reduces the power as well as the mass, often faster than it reduces the mass, and you end up with a worse ratio and a worse winter. The gains on paper assume FTP holds, and it frequently does not.

The bike is part of the system. On an 8 per cent climb your bike and kit are lifted by exactly the same gravity as you are. Nine kilograms of bike is nine kilograms. Swapping wheels or losing the saddlebag is a real, immediate, risk-free improvement, and it is the part most people ignore while agonising over the other number.

If you want to change your body composition, that is a conversation to have with a doctor or a registered dietitian who knows you, not with a calculator. What this page can do honestly is tell you what your current figure is, and what a kilogram is worth on a given hill.

## Where to find the watts instead

For most riders, there is far more available in the numerator than the denominator. A structured winter of threshold and VO2 work moves FTP by a meaningful margin in a way that is entirely within your control, repeatable, and makes you faster on the flat as well as uphill.

Twenty watts on an FTP of 240 is the same ratio gain as losing six kilograms, and one of those is a great deal more fun than the other.