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 UK stolen-bike databases 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.
Six reasons to know yours.
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.
- Proof of ownership. The primary evidence used for insurance claims, police reports and recovery after a theft. Without it, proving a bike is yours is genuinely hard.
- Theft recovery. UK police forces search stolen-bike registers by frame number. It is the key that links a recovered bike back to its owner.
- Registration services. UK stolen-bike databases require frame numbers to register your bike and deter thieves.
- Insurance requirement. Most bike insurers ask for the frame number on policies. A missing number may mean a bike cannot be insured.
- Resale trust. Serious buyers ask for the frame number before they travel. Being able to share it, and knowing yours is clean, shortens the sale.
- History tracking. Manufacturer databases can confirm production date, batch, recalls and warranty status from the frame number alone.
Start under the bottom bracket.
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 |
Road bikes
- Under the bottom bracket. Most common. Turn the bike upside down.
- Seat tube, near the bottom bracket (5–10 cm from the cranks).
- Head tube, near the fork. Check both sides.
- Rear dropout (wheel mount). Often on the right side.
- Inside the rear triangle. May require removing a wheel.
Mountain bikes
- Under the bottom bracket. Usually. Expect mud.
- Seat tube. Check both sides.
- Rear dropout or chainstay. Common on full-suspension frames.
- Head tube. Less common, but worth a look if the other spots come up blank.
Electric bikes
- Under the bottom bracket. Still the first place to look.
- Near the motor housing. Check all sides of the motor.
- Inside the battery compartment. Remove the battery first.
- Down tube. Often near the battery-integration point.
- Rear dropout. Especially on rear-hub-motor bikes.
Five steps. Ten minutes. Done.
By step five you'll have a photo, a verified number and a backup copy stored somewhere safe.
01Prepare your bike
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.
02Check the bottom bracket
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.
03Check alternative locations
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.
04Document it
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.
05Verify and register
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.
Four numbers on your bike. Only one is the frame number.
Here's how to tell the frame number apart from the rest, and why only one of them actually proves the bike is yours.
- Frame number (serial number).(primary ID)
- Location: Stamped into the frame metal
- Format: 7–14 alphanumeric characters
- Purpose: Unique bike identification
- Component serial numbers.
- Location: On individual parts (wheels, groupset)
- Format: Varies by manufacturer
- Purpose: Part identification
- Production / date code.
- Location: Often near the frame number
- Format: Usually 4–6 characters
- Purpose: Manufacturing date / batch
- Stolen-bike registry ID.
- Location: Sticker or etching you add
- Format: Varies by registry
- Purpose: Registration database link
The eight-point protection checklist.
Finding the number is step one. Protecting it, and the bike it belongs to, is the rest of this list.
- Photograph the frame number. Multiple angles. Store in cloud backup.
- Run a free stolen-bike check. Cross-check at Cyclesite's stolen-bike check before you register or insure.
- Register with a UK stolen-bike database. National cycle databases used by UK police. Free registration, searched on recovery.
- Add to your insurance policy. Most insurers need it on file. Update the policy documents.
- Record it on the purchase receipt. Keep the receipt with the frame number as proof of ownership.
- Mark the bike with a UV pen. Postcode in a hidden location gives you a secondary identifier.
- Store the number securely. A copy kept separate from the bike. Not in the shed or garage with it.
- Re-register annually. Revisit your stolen-bike database registration each year to keep details current.
Five common problems, five fixes.
If you can't find the number, if it's worn, or if it looks tampered with, this is where to start.
- The frame number is worn or faded
- Try rubbing the area with a soft pencil. Graphite highlights the engraving. Dusting with flour or talc can also help. Take photos with flash from several angles; a phone camera zoomed in often reads what the eye cannot.
- You can't find the frame number anywhere
- Check the original purchase receipt. It is usually listed there. Contact the retailer or manufacturer. Check any warranty documents or insurance policy. As a last resort, note the component serial numbers as weak secondary evidence.
- The frame number is on a sticker, not stamped
- Verify that it is a legitimate manufacturer sticker and check whether the same number is also stamped elsewhere. Contact the manufacturer to confirm their standard for that model. Photograph it. But be cautious, because stickers can be faked.
- The frame number appears tampered with
- Do not proceed if you're buying. If it's your own bike, contact the police and cross-check the databases immediately. Document with photos. Report to Action Fraud on 0300 123 2040.
- There are multiple numbers and you cannot tell which is which
- The frame number is usually the longest (7–14 characters) and is stamped into the frame itself, not onto components. Production codes are shorter. When in doubt, photograph everything and contact the manufacturer.
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.
Required on every listing. Masked in every display.
Frame numbers are central to how Cyclesite protects buyers and sellers.
- Mandatory. Every bike listed on Cyclesite needs a frame number before the advert goes live.
- Cross-checked. The number is run against UK stolen-bike databases. Flagged bikes are blocked and escalated.
- History record. We create a history record so the same bike can be tracked across listings, service events, and ownership transfers.
- Masked publicly. Full frame numbers aren't shown in public history records. We mask part of the number so owners recognise theirs without enabling cloning.
Frequently asked.
What is a bike frame number?
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 UK stolen-bike databases before a listing goes live.
Where is the frame number on most bikes?
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.
What does a bike frame number look like?
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.
Why can't I find my bike's frame number?
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.
Is the frame number the same as the serial number?
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.
What should I do after finding my frame number?
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.
Can I check if a bike is stolen by frame number?
Yes. Run it through Cyclesite's free stolen-bike check. It cross-checks UK stolen-bike databases 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.
What if the frame-number area looks tampered with?
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.
Do all bikes have frame numbers?
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.
How do I find the frame number on an e-bike?
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.
Can frame numbers be faked or changed?
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.
Didn't find your answer? Visit the help centre or contact support.
Got the number?
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Editorial standards
Last reviewed by the Cyclesite editorial team. Published by Cyclesite, Companies House No. 13238473.