Cycling speed calculator

How the calculator works

Pick what you want to find out. Then type your power or your speed, the slope of the road and your weight. The answer changes as you type. A watt is a measure of how hard you push on the pedals.

The calculator adds the weight of a typical road bike to your own weight. Then it works out the speed where your push on the pedals matches everything pushing back.

What slows a rider down

Three things push back as you ride.

• The slope. On a hill you lift your body and your bike up the road with every turn of the pedals. This is why your weight matters so much on a climb.
• Your tyres. They squash a little as they roll, and that takes a small, steady amount of power.
• The air. You push air out of the way as you go. It hardly matters at walking pace, but it grows fast as you speed up. To go twice as fast you need about eight times the power for the air.

On a flat road, the air takes most of your power. On a steep hill, lifting yourself up takes most of it. The three numbers under the answer show this split.

Where the numbers come from

The calculator uses the standard sum for cycling power. It adds up the power to climb, to roll the tyres and to push the air. Then it allows a little extra for the chain. In 1998, Martin and his team tested this sum against power meters on real roads and found it matched very closely. The Wikipedia page on bicycle performance sets out the same parts.

The sums use a typical road bike riding position, normal road tyres and calm air. They are the same sums the Couch to Climb app uses for its climbs.

Why your real speed will be different

Wind makes the biggest change. A headwind can take a lot off your speed on the flat, and a tailwind adds to it. Your clothes, how you sit on the bike and your tyres all play a part too. Use the answer as a rough guide.