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Frame numbers
Where to find a frame number and why it matters.
Where to find a frame number and why it matters.
A bike frame number (also called the serial number) is a unique alphanumeric identifier. Typically seven to fourteen characters. Stamped into the frame during manufacture. On most bikes you'll find it under the bottom bracket, where the pedal cranks meet the frame. It's the identifier UK police use to return stolen bikes, the identifier insurers require on policies, and the identifier Cyclesite cross-checks against international stolen-bike registries before a listing goes live.
Your bike's fingerprint. Without it you can't insure it, register it, recover it after a theft, or sell it to a confident buyer. Here's where it is, how to read it, and what to do with it.
Check a bike frame number
Free, instant, no signup. Enter a frame or serial number to check it against a stolen-bike registry and rider-filed theft reports.
From the insurance policy on your bike today to the stolen-bike database that recovers it tomorrow, the frame number is the thread that holds everything together.
That's where the overwhelming majority of frame numbers live. The table below lists alternatives by bike type.
| Bike type | Primary | Secondary | Tertiary |
|---|---|---|---|
| Road bike | Bottom bracket | Head tube | Seat tube |
| Mountain bike | Bottom bracket | Seat tube | Rear dropout |
| Hybrid / commuter | Bottom bracket | Seat tube | Head tube |
| Electric bike | Bottom bracket | Motor housing | Battery compartment |
| BMX | Bottom bracket | Head tube | Rear dropout |
| Folding bike | Main frame tube | Hinge area | Bottom bracket |
| Kids' bike | Bottom bracket | Seat tube | Under down tube |
By step five you'll have a photo, a verified number and a backup copy stored somewhere safe.
Move the bike to a well-lit area. Turn it upside down onto handlebars and saddle (cardboard under them protects your kit). Clean the bottom-bracket area with a cloth. Grab a torch, a camera and a notepad.
Look at the underside where the cranks meet the frame. The number is stamped into metal, not plastic. Wipe away grease and dirt. Use your torch from different angles. You are looking for 7-14 characters.
If the bottom bracket is blank: seat tube (both sides), head tube near the fork, rear dropout (right side is most common), inside the rear triangle. For e-bikes, check the motor housing and battery area.
Take a clear photo of the number, then a second wider photo showing where it sits on the bike. Write the number down carefully. Double-check it by reading forwards then backwards. Store the record somewhere that is not on the bike.
Run a free stolen check at Cyclesite's stolen-bike check. Register the bike on a UK stolen-bike database. It's free, takes five minutes, and UK police search them. Add the number to your insurance policy.
Here's how to tell the frame number apart from the rest, and why only one of them actually proves the bike is yours.
Finding the number is step one. Protecting it, and the bike it belongs to, is the rest of this list.
If you can't find the number, if it's worn, or if it looks tampered with, this is where to start.
Red flag: tampered frame numbers. If the frame-number area looks filed down, painted over, re-stamped or otherwise tampered with, that is a major warning sign of a stolen bike. Do not buy. Report the listing to Cyclesite and to the police immediately.
Frame numbers are central to how Cyclesite protects buyers and sellers.
A bike frame number (also called the serial number) is a unique alphanumeric identifier. Typically seven to fourteen characters. Stamped into the frame during manufacture. On most bikes you'll find it under the bottom bracket, where the pedal cranks meet the frame. It's the identifier UK police use to return stolen bikes, the identifier insurers require on policies, and the identifier Cyclesite cross-checks against international stolen-bike registries before a listing goes live.
Under the bottom bracket on most bikes. Flip the bike upside down, look where the pedal cranks meet the frame, and you will see characters stamped or engraved into the metal shell. If it is not there, check the seat tube, head tube or rear dropout. Some brands put it in unusual places.
Seven to fourteen characters, usually a mix of letters and numbers, stamped directly into the metal frame. Trek uses formats like "WTU" followed by numbers. Specialized starts with "WSBC". Each brand has its own system. If it looks hand-scratched or irregular, that is a warning sign.
Usually one of four reasons: worn or faded with age, covered in dirt and grease, located somewhere unusual for that brand, or the bike type puts it elsewhere (e-bikes often have it near the motor). Check your purchase receipt. The number is usually listed there. Clean the bottom-bracket area thoroughly. Contact the manufacturer if you are stuck.
Yes. Same thing, different name. The unique identifier stamped into your frame during manufacture. Not to be confused with component serial numbers on wheels, groupsets or forks. The frame number is what police use, what insurers want, and what registration databases store.
Photograph it clearly. Run it through a stolen-bike check to confirm nothing is flagged. Register it on a UK stolen-bike database. Free, five minutes. Add it to your insurance policy. Store a copy separate from the bike.
Yes. Run it through Cyclesite's free stolen-bike check. It cross-checks a stolen-bike registry and rider-filed theft reports in one go. Takes thirty seconds. If you're buying a used bike, do this before you travel. If the seller will not provide the frame number in advance, that tells you something.
Do not buy the bike. Tampered frame numbers almost always mean theft. Grinding marks, fresh paint over the area, stickers placed conveniently. All red flags. Walk away calmly, report the listing to us and to the police. Do not confront the seller.
Almost all modern bikes. Anything from a major brand has one. Very old bikes, cheap department-store bikes, and custom frames sometimes do not. If you are buying a used bike without a frame number, you have no way to verify it is not stolen. Factor that into your decision.
E-bikes complicate things because motors and batteries sit where frame numbers traditionally go. Check under the bottom bracket first anyway. Then look near the motor housing, inside the battery compartment with the battery removed, and along the down tube near where the battery integrates. Some brands stamp the number on a documentation plaque instead.
They can be ground off, filed down, or covered over. Professional thieves do this. That is exactly why tampered frame numbers are such a serious warning sign. Look for irregular surfaces, fresh paint in that specific area, or numbers that look re-stamped rather than factory-original. When in doubt, walk away.
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Register on a UK stolen-bike database for police-searchable protection.
Last reviewed by the Cyclesite editorial team. Published by Cyclesite, Companies House No. 13238473.
Brand-specific guides to where the frame number is stamped on your bike and how to read it, for the most common UK bike brands.