These numbers come from the same formulas as our bike size calculator: the height chart is a rounded consensus of the Giant Talon, Trek Marlin, Specialized Rockhopper and Canyon, checked in October 2026, and the inches by inseam are the classic bike shop math. Canyon labels one letter lower than the rest: its small is everyone else’s medium. Crank and saddle figures come from the crank length calculator and the saddle height calculator. Heights are rounded to the nearest inch, with centimeters alongside. For other types of bike, see the bike size chart by height.
Mountain bike size by height
| Size | Height | Height (cm) | Frame | Typical inseam |
|---|---|---|---|---|
| XS | up to 5 ft 2 in | up to 157 cm | 13-14 in | up to 28 in (72 cm) |
| S | 5 ft 2 in–5 ft 5 in | 157-165 cm | 15 in | 28-30 in (72-76 cm) |
| M | 5 ft 5 in–5 ft 9 in | 165-176 cm | 16-17 in | 30-32 in (76-81 cm) |
| L | 5 ft 9 in–6 ft 1 in | 176-185 cm | 18-19 in | 32-34 in (81-85 cm) |
| XL | 6 ft 1 in–6 ft 4 in | 185-193 cm | 19-20 in | 34-35 in (85-89 cm) |
| XXL | 6 ft 4 in and up | 193 cm and up | 21-22 in | 35 in (89 cm) and up |
The frame inches are the approximate seat tube length, the old way of sizing; today brands sell by letter and some still print the number alongside. The typical inseam is 46% of height.
Frame inches, crank and saddle height by inseam
| Inseam | Classic size (× 0.226) | MTB crank | Saddle height with that crank |
|---|---|---|---|
| 27 in (68.6 cm) | 15.5 in | 157.5 mm | 23.8 in (60.4 cm) |
| 28 in (71.1 cm) | 16.1 in | 157.5 mm | 24.8 in (62.9 cm) |
| 29 in (73.7 cm) | 16.6 in | 157.5 mm | 25.8 in (65.4 cm) |
| 30 in (76.2 cm) | 17.2 in | 162.5 mm | 26.5 in (67.4 cm) |
| 31 in (78.7 cm) | 17.8 in | 162.5 mm | 27.5 in (69.9 cm) |
| 32 in (81.3 cm) | 18.4 in | 165 mm | 28.4 in (72.2 cm) |
| 33 in (83.8 cm) | 18.9 in | 165 mm | 29.4 in (74.7 cm) |
| 34 in (86.4 cm) | 19.5 in | 167.5 mm | 30.3 in (76.9 cm) |
| 35 in (88.9 cm) | 20.1 in | 167.5 mm | 31.3 in (79.4 cm) |
| 36 in (91.4 cm) | 20.7 in | 170 mm | 32.2 in (81.7 cm) |
| 37 in (94.0 cm) | 21.2 in | 170 mm | 33.2 in (84.2 cm) |
Compare the two charts and you’ll see the classic math gives roughly an inch more than the label for your height: a 32 in inseam, normal for someone about 5 ft 9 in, gives 18.4 in, while height puts that rider on a 16-17 in medium. Modern mountain bikes tend to have shorter seat tubes to fit long dropper posts, so if the two don’t match, go by height.
For the crank we take 2.5 mm off the current road trend so the pedals hit fewer rocks and roots. Saddle height is measured from the center of the bottom bracket to the top of the saddle, along the seat tube, with the dropper fully extended.
If you’re between two sizes
If you’re within about half an inch (1.5 cm) of a cutoff, let your inseam decide. With long legs for your height (more than 47.5% of your height), go smaller: the bike is easier to throw around and you run more seatpost. With a long torso (less than 44.5%), go bigger to stretch out the reach.
| Height at the cutoff | Choosing between | Pick the smaller size if your inseam is | Pick the larger size if it’s |
|---|---|---|---|
| 5 ft 2 in (157 cm) | XS or S | over 29.4 in (74.6 cm) | under 27.5 in (69.9 cm) |
| 5 ft 5 in (165 cm) | S or M | over 30.9 in (78.4 cm) | under 28.9 in (73.4 cm) |
| 5 ft 9 in (176 cm) | M or L | over 32.9 in (83.6 cm) | under 30.8 in (78.3 cm) |
| 6 ft 1 in (185 cm) | L or XL | over 34.6 in (87.9 cm) | under 32.4 in (82.3 cm) |
| 6 ft 4 in (193 cm) | XL or XXL | over 36.1 in (91.7 cm) | under 33.8 in (85.9 cm) |
Between those values, both fit. For enduro and downhill, many riders prefer the larger size for stability; for slow, technical trail riding, the smaller one.
Before you buy
Two larges from different brands can have quite different reach (the horizontal distance from the bottom bracket to the head tube), and on a mountain bike you feel it. Compare the model you like with your current bike in the bike geometry comparison, and measure your inseam as explained in the guide to finding your bike size. Kids’ bikes are sized by wheel diameter, not frame: see kids’ bike size by age.
Frequently asked questions
What size mountain bike do I need if I'm 5'7"?
A medium, which works out to a 16-17 in frame. A medium covers 5 ft 5 in to 5 ft 9 in (165-176 cm), so at 5 ft 7 in (170 cm) you're right in the middle of the range.
What size is a 17-inch mountain bike?
A medium, for riders 5 ft 5 in to 5 ft 9 in (165-176 cm). A 15 in frame is a small (5 ft 2 in to 5 ft 5 in) and an 18-19 in frame is a large (5 ft 9 in to 6 ft 1 in).
How do I work out frame inches from my inseam?
Multiply your inseam in centimeters by 0.226, or your inseam in inches by 0.574. A 32 in (81.3 cm) inseam gives 18.4 in. This math usually gives an inch more than the label on your size by height; if they don't match, go by height.