Bike size guide: frame, wheel size and height
Two different numbers get called "bike size", and mixing them up is the reason a lot of people end up on a bike that does not fit.
Frame size decides whether you can stand over the bike, reach the bars and get a comfortable leg extension. It is about your body.
Wheel size decides how the bike rolls, how it handles and how it fits in a car or a hallway. It is about the bike's job, not your height.
Get the frame right and the wheel choice becomes a preference. Get the frame wrong and no amount of adjustment will fix it.
Frame size from your height
The starting point is your height. This table is the conventional guide for adult bikes and is accurate enough to narrow the choice to one or two sizes.
| Rider height | Frame size (cm) | Frame size (inches) | Letter |
|---|---|---|---|
| 4'11" - 5'2" (150-157 cm) | 47-50 cm | 14-15.5" | XS |
| 5'2" - 5'5" (157-165 cm) | 50-53 cm | 15.5-16.5" | S |
| 5'5" - 5'8" (165-173 cm) | 53-55 cm | 16.5-17.5" | M |
| 5'8" - 5'11" (173-180 cm) | 55-57 cm | 17.5-18.5" | M/L |
| 5'11" - 6'1" (180-185 cm) | 57-59 cm | 18.5-19.5" | L |
| 6'1" - 6'4" (185-193 cm) | 59-62 cm | 19.5-21" | XL |
Why height alone is not enough
Two people of the same height can need different frame sizes, because leg length varies. The measurement that actually matters is your inside leg, taken from the floor to your crotch while standing against a wall with your feet slightly apart, ideally in the shoes you will ride in.
A common formula for road bikes: inside leg in cm × 0.65 = frame size in cm. For a mountain bike, subtract 2-4 cm from that figure, because you want more standover clearance and a shorter reach for technical terrain.
If you are between sizes, the general rule is:
- Road and gravel: go smaller. A slightly smaller frame is easier to make fit with a longer stem and seatpost; a frame that is too big cannot be shrunk.
- Mountain bike: go smaller, for the same reason plus more clearance.
- City and hybrid: go larger. You want a more upright position, and a slightly bigger frame gives it without a tower of spacers.
Frame size from inside leg, by bike type
If you have your inside leg measurement, this is more precise than the height table.
| Inside leg | Road frame | MTB frame | Hybrid / city frame |
|---|---|---|---|
| 70-75 cm | 47-49 cm | 13-14" | 15-16" |
| 75-80 cm | 49-52 cm | 15-16" | 17-18" |
| 80-85 cm | 52-55 cm | 17-18" | 19-20" |
| 85-90 cm | 55-58 cm | 19-20" | 21-22" |
| 90-95 cm | 58-61 cm | 21-22" | 23-24" |
Note that mountain bike frames are quoted in inches while road frames are quoted in centimetres. That is a convention, not a conversion, so do not mix the two columns up.
Wheel size: a separate decision
Wheel size does not need to match your height. It needs to match what you are doing.
| Wheel | Best for | Trade-off |
|---|---|---|
| 12-14 inch | Balance bikes and first pedal bikes, ages 2-5 | Very limited range of use; outgrown quickly |
| 16 inch | Ages 4-6, first proper pedal bike | Fine on smooth ground only |
| 20 inch | Ages 6-9, kids' MTBs and BMX | Good balance of size and capability |
| 24 inch | Ages 8-11, and small adults | Rolls better, still manageable |
| 26 inch | Adults, MTB, e-bikes, fat bikes | The most common adult size; huge choice |
| 27.5 inch | Mountain bikes, some hybrids | Better rollover than 26, still nimble |
| 29 inch | Mountain bikes, tall riders | Rolls over obstacles best, slower to accelerate |
| 700c | Road, gravel, hybrids, city | The standard adult road size (roughly 29 inch) |
Two things trip people up here.
700c and 29 inch are almost the same diameter (622 mm bead seat). A 700c road wheel and a 29-inch MTB wheel take different tyres and are built differently, but the diameter is close. If you are comparing a hybrid with 700c wheels to a mountain bike with 29-inch wheels, you are comparing similar diameters with very different tyres.
Fat bikes use a standard diameter with an enormous tyre. A 26-inch fat bike has 26-inch rims and tyres up to 4 or 5 inches wide, which makes the overall diameter close to a 29er. That is why they roll over things well and why they are heavy.
What actually determines fit on the bike
Frame size gets you in the door. These three adjustments decide whether the bike is comfortable:
Saddle height. With your heel on the pedal at the bottom of the stroke, your leg should be almost straight, with a slight bend. If your hips rock when you pedal, the saddle is too high. If your knee is visibly bent at the bottom, it is too low. This single adjustment affects comfort and efficiency more than anything else on the bike.
Saddle setback and angle. Fore and aft position affects where your knee sits over the pedal. A saddle tilted nose-down to relieve pressure is a sign the fit is wrong somewhere else, not a fix.
Reach. If you are stretched out with locked elbows, the frame is too long, or the stem is. If your knees hit the bars, it is too short. A stem swap is cheap and reversible; a frame swap is not.
A note on e-bikes and folding bikes
E-bikes often come in fewer frame sizes, because the battery and motor integration makes extra tooling expensive. Many are sold as "one size" or "step-through" with an adjustable seatpost range. Check the rider height range in the listing rather than the nominal frame size; that is the number that matters.
Folding bikes are similar: the frame is designed around the fold, so sizing is expressed as a height range. A 20-inch folding bike typically suits riders from about 5'0" to 6'2", but the usable range is narrower than a conventional bike because the handlebar height is less adjustable.
If you are between two sizes
Buy the smaller one and adjust upward. A longer seatpost and stem can add reach and height. You cannot remove material from a frame that is too big, and a bike that is too large is uncomfortable in a way that no adjustment fixes.
The exception is a city bike where you want a very upright position and the smaller frame would need an absurdly long seatpost. In that case, the larger frame is the better starting point.
Measuring yourself properly
You need three numbers, and you can take them at home with a tape measure and a wall.
- Height: against a wall, barefoot, heels together.
- Inside leg: a book held firmly between your legs as if it were a saddle, spine against the wall, measure floor to the top of the book.
- Arm length: shoulder joint to wrist, arm straight.
Write them down before you shop. A seller who asks for them is a seller who knows what they are doing, and you will get a better answer than "what size am I" ever produces.