A Brompton has two important numbers: a frame number and a serial number. The frame number is stamped into the frame, usually near the crank area, close to the rear triangle hinge and bottom bracket. The serial number is different: on newer Brompton bikes it is usually on the identification plate on the seat tube, and on older bikes it may be on a sticker below the seat post clamp. You may need both numbers when registering the bike, checking ownership, buying used, reporting theft or proving the bike is yours.
That number matters. It helps you register the bike, check if it has been reported stolen, prove ownership, value it and sell it with more buyer confidence. Here is where to find it, how to read it, and how to check it before you buy.
Check a Brompton frame number
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On a Brompton the frame number is usually stamped into the frame near the crank and rear triangle hinge area. The serial number is usually on the seat tube identification plate on post-2016 bikes, or on a sticker below the seat post clamp on pre-2016 bikes.
Start near the crank and rear triangle hinge.
On a Brompton the frame number is usually stamped into the frame near the crank area, close to the rear triangle hinge and bottom bracket. It can be smaller and harder to spot than the large stickers on some other bikes, so take your time.
- Fold or position the bike so you can see the crank area clearly.
- Look around the rear triangle hinge and bottom bracket area.
- Clean away dirt, oil or road grime.
- Use a phone torch and check from different angles.
- Look for a stamped number in the frame.
- Take a clear photo once you find it.
Make sure you copy the full number. A single missing or misread character can give the wrong result.
What does a Brompton frame number look like?
A Brompton frame number should be on the frame, not on a wheel, tyre, hub gear or component. It is the unique identifier stamped into the bike, not the model line or configuration code.
Do not use the model name, tyre size, barcode on a shop label, or any number printed on a component. The frame number belongs to the bike frame itself. For example, these are not usually the frame number:
- Brompton C Line
- Brompton P Line
- Brompton T Line
- Brompton A Line
- M6L
- H6L
- S Type
- M Type
- 16 inch
- Tyre markings
- Hub gear codes
- Brake or component codes
The number you want is the unique frame code that belongs to the frame itself.
Frame number or serial number: what is the difference?
Brompton uses both terms, and they are not always the same number. The frame number is stamped into the frame, the physical identifier on the bike itself. The serial number is the 10-digit number used for Brompton registration and model identification. Brompton says the first four digits show the production year and month, so a serial number starting with 1903 means the bike was made in March 2019. If you are buying a used Brompton, ask for both numbers if possible.
Where to find the Brompton serial number
The serial number is usually easier to find than the frame number.
- On post-2016 Brompton bikes, check the identification plate on the seat tube, the upright tube the seat post slides into.
- On pre-2016 Brompton bikes, check for a sticker below the seat post clamp.
- The serial number should be 10 digits.
What does a Brompton serial number look like?
A Brompton serial number is 10 digits long. The first four digits show the year and month of manufacture. Use the full 10-digit number when registering the bike or checking details, not only the first four digits.
- 1903 means March 2019
- 2206 means June 2022
- 2401 means January 2024
The detail that protects you.
A frame number is one of the most useful details on a used bike. It connects a Brompton to its owner, its registration record and any stolen-bike reports.
You may need it to:
- Check if a Brompton bike has been reported stolen.
- Register your bike.
- Sell your bike with confidence.
- Get an accurate bike valuation.
- Make an insurance claim.
- Report a stolen bike to the police.
- Prove the bike is yours.
If you own a Brompton, take a photo of the frame number and keep it with your receipt. If the bike is ever stolen, that detail can make a real difference.
Buying a used Brompton? Check the frame number first.
Used Brompton bikes are in strong demand because they hold value well and are easy to store, commute with and carry on public transport. That also means you should check the details before paying. Before buying, ask the seller for:
- A clear photo of the frame number.
- A clear photo of the serial number.
- The original receipt or proof of purchase.
- The model line, handlebar type and gearing.
- Photos of both sides of the bike.
- Details of any upgrades or replacement parts.
- A clear reason for sale.
Red flag. Be careful if the seller refuses to show the frame number, says they cannot find it, gives only a partial code, or pressures you to pay quickly. A genuine seller should understand why you are checking.
Check a Brompton frame number on Cyclesite
Found the number? Run a free stolen-bike check before you buy. Enter the Brompton frame number into the checker and look for any matching reports. It only takes a moment, and it can help you avoid buying a bike with a bad history. If the bike looks clear, you can also value it and compare similar Brompton bikes for sale.
What if the Brompton serial plate or sticker is missing?
A missing serial plate or sticker does not always prove there is a problem. Older stickers can come away and used bikes can lose labels over time. But you should be careful. If the serial number is missing:
- Check for the stamped frame number.
- Ask for the original receipt.
- Ask for Brompton registration details.
- Ask the seller where and when the bike was bought.
- Check the bike carefully against the advert.
- Walk away if the story does not add up.
If the frame number itself has been scratched off, filed down or deliberately damaged, do not buy the bike.
What to do if your Brompton has been stolen.
Report it as soon as possible. You will usually need the frame number, photos, make, model, colour, size, location and any unique marks or upgrades.
- Report the theft to the police.
- Get a crime reference number.
- Add the bike to stolen-bike databases.
- Update any existing bike registration record.
- Contact your insurer if you have cover.
- Watch used bike listings for matching bikes.
- Keep photos, receipts and messages in one place.
Include anything distinctive, such as upgraded wheels, unusual tyres, scratches, stickers, lights, mudguards, racks or replacement parts. The more detail you provide, the easier it is to identify the bike if it appears for sale.
Brompton frame number FAQs
Is the Brompton frame number the same as the serial number?
No, not always. Brompton uses a frame number stamped into the frame and a 10-digit serial number used for registration and dating the bike.
Where is the serial number on a post-2016 Brompton?
On post-2016 Brompton bikes, the serial number is usually on the identification plate on the seat tube.
Where is the serial number on a pre-2016 Brompton?
On pre-2016 Brompton bikes, the serial number is usually on a sticker below the seat post clamp.
How many digits is a Brompton serial number?
A Brompton serial number is 10 digits long. The first four digits show the production year and month.
Can I tell the age of a Brompton from the serial number?
Yes. Brompton says the first four digits of the serial number show the year and month of manufacture. For example, 1903 means March 2019.
Where is the frame number on a Brompton C Line?
Check near the crank area, close to the rear triangle hinge and bottom bracket area. Also check the seat tube identification plate for the serial number.
Where is the frame number on a Brompton Electric?
Check near the crank area for the frame number and the seat tube plate for the serial number. Brompton Electric bikes may also have electrical system details, but those are separate from the frame number.
What if the Brompton frame number has been removed?
Do not buy the bike. A removed or damaged frame number is a major warning sign and can make the bike hard to register, insure, resell or prove as yours.
Can I check if a Brompton is stolen by frame number?
Yes. Use the frame number or serial number to run a stolen-bike check before buying. You should also ask for proof of ownership and check that the bike details match the seller’s paperwork.
Looking for another brand? See the full bike frame number guide.
Bottom line
A Brompton has a frame number and a serial number, and both are worth checking. The frame number is usually stamped near the crank and rear triangle hinge area. The serial number is usually on the seat tube plate on newer bikes, or on a sticker below the seat post clamp on older bikes. If you are buying used, ask for both numbers, check them before paying and keep a record once the bike is yours.
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Last reviewed by the Cyclesite editorial team. Published by Cyclesite, Companies House No. 13238473.