Buying Guides

What Size Bike Frame Do I Need? UK Height Chart (16, 17, 18, 19 Inch)

DDuncan McGregor ·17 August 2026 ·3 min read

Frame size is the one thing people get wrong when they buy a bike online — and the one thing that can't be fixed afterwards. Wrong saddle? Swap it. Wrong tyres? Swap them. Wrong frame, and you're sending the bike back.

Here's the short version: frame size is measured in inches, from the centre of the bottom bracket to the top of the seat tube. It's not the wheel size, and it's not quite the same as Small/Medium/Large — though most brands print both. This guide gets you to the right number in about two minutes.

The quick answer — adult frame size by height

Your height	Frame size	Typical label
4’11" – 5’3" (150–160cm)	14–15 inch	X-Small
5’3" – 5’6" (160–168cm)	15–16 inch	Small
5’6" – 5’9" (168–175cm)	16–17 inch	Small / Medium
5’9" – 6’0" (175–183cm)	17–18 inch	Medium
6’0" – 6’3" (183–190cm)	19–20 inch	Large
6’3" – 6’6" (190–198cm)	21–22 inch	X-Large

If you fall between two sizes: size down for mountain biking, size up for road and long-distance riding. A smaller frame is easier to throw around off-road; a larger one gives a longer, more comfortable reach for hours in the saddle.

16 inch frame bikes 17 inch frame bikes 18 inch frame bikes 19 inch frame bikes 20 inch frame bikes 22 inch frame bikes Small frame Medium frame Large frame XL frame

Why the same height gives different sizes on different bikes

Mountain bikes are measured on the seat tube and typically run 14–22 inch. Modern MTBs build in lots of standover clearance, so a 17" mountain bike fits a shorter rider than a 17" hybrid would. Riding technical terrain? Sizing down gives you room to move over the bike.

Hybrid bikes use similar numbers with a more upright position — a hybrid at your size will feel roomier than the equivalent mountain bike.

Road bikes are usually sized in centimetres — 48, 52, 56cm. Rough conversion: divide by 2.54. But road geometry is long and low, so don't cross-shop the numbers directly.

Electric bikes often come in just two frames — like Crossbar and Low Step — because the motor and battery constrain the design. Go by the stated rider-height range instead (we print it on every e-bike listing).

The measurement that actually matters: inside leg

Two people the same height can have very different leg lengths, so inside leg beats a height chart:

1. Stand against a wall in your riding shoes, feet about 15cm apart.

2. Put a book between your legs, spine up, snug — the same pressure as a saddle.

3. Mark the top of the book on the wall and measure down to the floor.

Bike type	Formula	Example: 32" inside leg
Mountain bike	inside leg (in) × 0.66	≈ 21 inch frame
Hybrid	inside leg (in) × 0.685	≈ 22 inch frame
Road	inside leg (cm) × 0.665	≈ 54cm frame

Standover height — the safety check

Whatever the chart says, you must be able to stand flat-footed over the top tube with clearance: 2–4 inches on a mountain bike, 1–2 on a hybrid, 1 inch on a road bike. No clearance means an emergency stop ends with you landing on the frame — the most common cause of a bad first ride on a new bike.

Kids' bikes are sized by wheel, not frame

Age	Child height	Wheel size
2–4	85–100cm	12 inch
3–5	95–110cm	14 inch
4–6	105–120cm	16 inch
5–8	115–135cm	20 inch
7–11	130–150cm	24 inch
10+	145cm+	26 inch / small adult

Resist buying big "to grow into". A child on an oversized bike can't reach the brakes or put a foot down confidently — they learn slower and give up sooner. Full details in our kids' bike sizing guide.

Common sizing mistakes

❌ Buying by wheel size on an adult bike. A 29er and a 27.5 can both come in a 17" frame — the wheel affects how it rolls, not whether it fits.

❌ Assuming Medium is Medium. One brand’s Medium is 17", another’s is 18". Check the inch figure on the spec sheet.

❌ Ignoring reach. Right height but stretched or cramped over the bars? That’s reach — often fixable with a different stem, but worth knowing first.

❌ Sizing up "for value". You get less bike, not more.

Still not sure?

Tell us your height and inside leg and we'll tell you which frame to order — and if it's wrong when it arrives, our 90-day no-quibble returns cover you. Or answer four quick questions in the Bike Finder.