Wondering whether you need a separate cadence sensor? If your power meter sits in the crank, it already counts pedal strokes. Hub-based meters and plain bikes are where a cheap add-on still earns its place.
This page is part of our wider guide to cycling gear.
| Item | Value |
|---|---|
| How a crank or spider power meter calculates power | Strain gauge deflection plus pedaling cadence |
| Where strain-gauge power meters are mounted | Bottom bracket, rear freehub or crankset |
| Garmin Cadence Sensor 2 mounting | Crank arm, with rubber bands |
| Garmin Cadence Sensor 2 battery | User-replaceable CR2032, about 12 months at one hour of daily use |
| Garmin Cadence Sensor 2 Bluetooth connections | Up to two devices at once |
Figures come from Wikipedia’s cycling power meter entry and a retailer’s product page. Specifications and battery claims can change, so check the source before you rely on them.
What a cadence sensor actually does
A cadence sensor counts how fast your cranks turn, in revolutions per minute. It does nothing else: it cannot measure force, so it cannot tell you watts.
That makes it a small, cheap accessory. It tells you whether you are spinning light and fast or grinding a heavy gear, which is useful for pacing and for working on your pedaling technique.
Cadence also feeds into other data. Riders can use power meters to experiment with cadence and see how it affects speed and heart rate, as the Wikipedia entry on power meters points out.
Does your power meter already measure cadence?
Often, yes. Crank and spider power meters work out power from strain gauge deflection and pedaling cadence, so the meter has to know your cadence to produce a watts figure.
Many units then pass that cadence on to your head unit alongside power. If you have one of these, a separate sensor is usually redundant. Check your head unit’s sensor screen: if cadence appears once you pair the power meter, you are done.
The picture is less clear for other mounting points. Strain-gauge meters are mounted in the bottom bracket, rear freehub or crankset, and not every design reports cadence in the same way, so read the specification of your exact model.
Hub-based meters are the usual exception
A freehub power meter uses the same strain gauges as a crank meter, but it sits in the rear wheel hub and measures power at the rear wheel. Because the wheel turns on its own when you coast, a hub does not directly sense your pedaling rate in the same way a crank does.
If you ride a hub meter and want cadence on screen, plan on adding a dedicated sensor. Check your meter’s manual first, since some models handle this differently.
When a separate cadence sensor still makes sense
There are a few situations where buying one is the sensible choice:
- You have no power meter and want cadence data for training or technique work.
- You use a hub-based power meter that does not give you cadence.
- You ride a trainer with a basic setup and your app wants a cadence signal.
- Your current meter’s cadence is missing or unreliable and you want a second reading.
If none of those fit, keep your money. Spend it on something that changes your training, such as a heart rate monitor for cycling, which adds a different kind of information next to power.
What to look for in a cadence sensor
Most buyers only need to check three things: how it mounts, how it connects, and how long the battery lasts.
Mounting
Older designs used a magnet on the crank and a sensor on the frame, which meant aligning parts. Newer magnetless models are simpler. The Garmin Cadence Sensor 2, for example, mounts directly to your crank arm with rubber bands, with no fiddly spoke magnets to install, according to the retailer page.
Connectivity
Look for a sensor that speaks the same language as your gear. On that retailer page, ANT+ pairs with Edge computers and most cycling head units, while Bluetooth Low Energy connects to smartphones running training apps. If you are unsure which you need, our comparison of ANT+ vs Bluetooth cycling sensors explains the trade-offs.
The same page says the sensor broadcasts to unlimited ANT+ devices at once and pairs with up to two Bluetooth devices. That covers an indoor session where you run both a head unit and a phone app.
Battery
Coin cells keep these sensors small. The user-replaceable CR2032 battery in this example runs approximately 12 months at one hour of daily use, per the retailer. A red LED flash after two crank revolutions signals a dropping battery, so you get a warning before it stops transmitting.
Those are one retailer’s claims for one product, as of the page we checked. Confirm them with the manufacturer before buying.
A simple decision guide
- Check whether your power meter is crank, spider or pedal based. If so, test whether cadence shows on your head unit after pairing.
- If cadence appears, you do not need a separate sensor.
- If you have no power meter, or your hub meter does not provide usable cadence, pick a magnetless sensor that matches your head unit’s ANT+ or Bluetooth support.
- Pair it, spin the cranks, and confirm the number moves on your screen.
Whichever route you take, remember that cadence is context, not a goal. There is no single ideal rate for everyone, so use the number to learn how you ride rather than to chase a target.
Frequently asked questions
Can a cadence sensor measure power?
Show answer
No. It counts crank rotation only. Cadence alone cannot determine power; most cycling power meters also use strain gauges to measure torque.
Do I need a cadence sensor with a crank-based power meter?
Show answer
Usually not. Crank power meters calculate power from strain gauge deflection and pedaling cadence, and many report that cadence to your head unit.
Do hub power meters give cadence?
Show answer
Not reliably in the same way. A freehub meter measures power at the rear wheel, so a dedicated cadence sensor is the safer option if you want that number.
Should I choose ANT+ or Bluetooth?
Show answer
Match your head unit or app. Many sensors, such as the Garmin Cadence Sensor 2 described by one retailer, support both.
How often does the battery need replacing?
Show answer
One retailer rates the Garmin Cadence Sensor 2’s CR2032 at approximately 12 months at one hour of daily use. Your mileage will vary with riding time.
