Cycling power zones and FTP explained

What watts, cadence and FTP mean

Watts measure power: how much work you are doing each second. On a bike, power depends on two things: how hard you push on the pedals (torque) and how fast you turn them. Double either one and, roughly speaking, you double the power.

Cadence is how fast you turn the pedals, in revolutions per minute (rpm). A sensor near the crank or flywheel counts each turn. Cadence alone does not tell you power, because 80 rpm against light resistance and 80 rpm against heavy resistance are very different efforts.

FTP, or functional threshold power, is an estimate of the highest average power you can hold for about an hour. Few people ride flat out for an hour to find it. A widely used shortcut is to ride a hard, steady 20 minutes and take 95% of that average power. Many apps run their own FTP tests and give you the number at the end.

The seven Coggan power zones

The most widely used zone system was set out by Dr Andrew Coggan. Each zone is a band of power as a percentage of FTP. Apps and classes may use different names or fewer zones, but most are based on these bands. The zones describe effort levels only: how hard a ride or interval feels and how long it can be held.

For example, with an FTP of 200 W, Zone 2 runs from 112 to 150 W and Zone 4 from 182 to 210 W. Our bike power zones tool does the sums for any FTP and rounds to the nearest watt.

Work out your zones in watts →

How spin bikes estimate watts

Road bikes with power meters measure force directly, using strain gauges in the pedals, cranks or hub. Most home spin bikes do not. Instead they measure cadence or flywheel speed, read the resistance setting, and look up a power figure from a table the maker built for that model. Bikes with motorised magnetic resistance know the exact magnet position, so their estimate is usually more consistent than a bike with a manual friction knob.

This matters in three ways. First, the watts on two different bikes may not match, so an FTP from your gym bike may not suit your home bike. Second, a bike whose resistance drifts as a felt pad wears or as parts warm up will drift in its watts too. Third, a bike with no resistance sensor cannot show watts at all, only cadence and a speed estimate.

If you want consistent numbers, look for a bike that lists power output and Bluetooth FTMS support, such as the smart bikes in our Peloton alternative guide. Then test your FTP on that bike and keep using it.

Using cadence and resistance without a power meter

Plenty of spin bikes show cadence but no watts. You can still ride by effort. Many classes give a cadence range and a resistance cue, such as 80 to 90 rpm at a firm resistance. Keep a note of the knob position and cadence that feels steady, hard and very hard to you, and reuse them.

You can also add a cheap cadence sensor to the crank arm and pair it with an app. That gives you rpm on a phone or tablet but still not watts. Our guide to using Zwift or the Peloton app on any bike explains what each type of sensor can and cannot send.

• Cadence only: rpm, no power
• Cadence plus resistance sensor: estimated watts from the maker's table
• Smart bike with FTMS: watts and cadence sent to apps over Bluetooth
• Power meter pedals or cranks: measured watts, most consistent

Setting and updating your FTP

Start with an app's FTP test or the 20-minute method, on the bike you will use for training. Warm up well first, as most test plans describe. Ride the 20 minutes as evenly as you can, then multiply the average power by 0.95. If you have a medical condition or have not exercised for a while, ask your GP before doing a maximal test.

Re-test now and then on the same bike, at a similar time of day, with the bike set up the same way. Our spin bike set-up guide covers saddle and bar position, which affects how comfortable a long effort feels.

Note:An all-out test is hard. Stop if you feel unwell, dizzy or have chest pain, and seek medical advice.

Frequently asked questions

What are FTP zones? They are bands of power set as a percentage of your functional threshold power. The Coggan model has seven, from Z1 below 55% to Z7 above 150% of FTP. Use our zones tool to see them in watts.

Do I need a spin bike with a power meter? No. You can ride by cadence and feel. A bike that shows watts helps if you want to follow zone-based workouts or apps that set targets in watts. See our best spin bike guide for options.

What spin bike cadence should I aim for? Classes commonly use ranges from about 60 rpm on heavy climbs to 100 rpm or more on light, fast efforts. There is no single right number; follow the cue and keep the movement smooth.

Why is my FTP lower on a different bike? Each bike estimates watts its own way, so numbers vary between models. Set zones from a test on the bike you ride most.