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Bike size calculator: frame size and saddle height from your inseam

Find the frame size that fits you for a road, gravel, mountain or hybrid bike from your inseam, with a starting saddle height.

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Frame size (cm)

54 cm

Usually size M

Frame size (inches)

21.3 in

Saddle height (center of crank to top of saddle)
28.3
Usual crank length
170.0 mm

Frame size for other inseams

Frame size (cm)Saddle height (center of crank to top of saddle)
28 in current4724.7
30 in current5126.5
31 in current5227.4
32 in current5428.3
33 in current5629.1
34 in current5730.0
36 in current6131.8

Why frame size matters

A bike that fits lets you pedal efficiently, handle well and ride for hours without knee, back or neck pain. Frame size is the first decision. The most reliable starting point is your inseam, the length of your legs, rather than your overall height, because people of the same height can have very different leg lengths.

The rules of thumb

  • Road and gravel bikes: frame size (cm) ≈ inseam in cm × 0.665
  • Mountain bikes: frame size (in) ≈ inseam in cm × 0.226
  • Hybrid and city bikes: frame size (cm) ≈ inseam in cm × 0.68
  • Saddle height ≈ inseam × 0.883, from the center of the crank axle to the top of the saddle

Road frames are usually sold in centimeters (52, 54, 56), mountain bikes in inches or letters (S, M, L).

How to measure your inseam

  1. Stand barefoot against a wall, feet about 6 inches apart.
  2. Pull a hardcover book up firmly between your legs, spine up, as a saddle would sit.
  3. Measure from the floor to the top of the spine, and repeat twice to be sure.

Worked example

A rider with a 32-inch (81.3 cm) inseam is shopping for a road bike.

  1. Frame size: 81.3 × 0.665 = 54 cm, usually a medium.
  2. For a mountain bike: 81.3 × 0.226 = about 18.4 in, also often a medium.
  3. Saddle height: 32 × 0.883 = 28.3 in (71.8 cm).

Typical road bike sizes

Inseam Frame size Usual size
28 in (71 cm) 47 cm XS
30 in (76 cm) 51 cm S
32 in (81 cm) 54 cm M
34 in (86 cm) 57 cm L
36 in (91 cm) 61 cm XL

Beyond the formula

  • Check the brand’s chart. Frame geometry varies, and one maker’s 54 can fit like another’s 56. Many brands list sizes by height and inseam.
  • Reach matters too. If you have a long torso and arms, you may prefer the larger of two sizes; a short torso, the smaller.
  • Standover clearance: you should be able to straddle the top tube with 1 to 2 inches of clearance on a road bike, more on a mountain bike.
  • Between sizes? The smaller frame is easier to adjust with a longer stem and seatpost; a frame that is too big cannot be made smaller.
  • Test ride when you can, and consider a professional bike fit if you ride long distances.

Frequently asked questions

What size road bike do I need?

Multiply your inseam in centimeters by 0.665 to estimate the frame size. A 32-inch (81 cm) inseam suggests a frame of about 54 cm, usually a medium.

How do I measure my inseam for a bike?

Stand barefoot against a wall with your feet 6 inches apart, pull a hardcover book up firmly between your legs like a saddle, and measure from the floor to the top of the book.

What size mountain bike do I need?

Mountain bikes are smaller for the same rider: multiply your inseam in centimeters by 0.226 to get a frame size in inches. A 32-inch inseam gives about an 18-inch frame, often a medium.

How high should my saddle be?

A common starting point is inseam × 0.883, measured from the center of the crank to the top of the saddle. Fine-tune so your knee keeps a slight bend at the bottom of the stroke.

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Results are estimates provided for information purposes. They do not replace professional advice.

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