How to measure your inseam

Your inseam, or inside leg, is the distance from the floor to your crotch. It’s the measurement that settles a bike size. You need a hardback book, a wall, a pencil and a tape measure.

  1. Back to the wall, shoes off. Pull a hardback book up between your legs, spine up, as firmly as a saddle.

  2. Keep the book level and mark the wall at its top edge.

  3. Step away and measure from the floor to the mark. That’s your inseam.

A man in a red cycling jersey and black cycling shorts stands barefoot with his back to a wall, holding a blue hardback book level and pressed up at his crotch, marking its top edge with a pencil
Measure from the book’s top edge to the floor.
  1. Take your shoes off and stand with your back flat to a wall, feet about 15–20 cm (6–8 in) apart.
  2. Pull a hardback book up between your legs, spine up, as firmly as a bike saddle would sit.
  3. Keep the book level and mark the wall at its top edge.
  4. Step away and measure from the mark to the floor, in cm or inches.
  5. Do it twice. Most people are 1–2 cm out the first time.

How do I measure a child’s inseam?

A girl of about seven in socks stands with her back to a wall while her mother, kneeling beside her, holds a red hardback book level between her legs and marks the book’s top edge with a pencil
Measure from the book’s top edge to the floor.

Use the same book method with the child in socks, and ask them to stand tall. If they won’t stand still, Cycling UK suggests a second way:

  • Standing heightMeasure them standing against a wall.
  • Sitting heightSit them on the floor against the wall and measure to the top of the head.
  • Inside legStanding height minus sitting height.

Source: Cycling UK.

Common mistakes

  • Measuring in shoesShoes add height and push you towards a bigger size.
  • Book too lowPull it up as firmly as a saddle.
  • Trouser inseamThe inseam on your jeans label is not your inside leg.

What is my inseam used for?

Bike size calculator

Inseam × 0.665 checks your road frame size.

Kids’ bike size chart

The inseam picks the wheel size.

Road bike size chart

Standover: your inseam minus the frame’s standover height.

Inseam questions

Is my inseam the same as my trouser inseam?

No. A trouser inseam is where the hem falls, which depends on the cut and how you like to wear it. For a bike, measure your body with the book method.

How exact does it need to be?

To about a centimetre. For a road frame, 1 cm of inseam moves the frame estimate by about 0.7 cm (inseam × 0.665), so measuring twice and taking the average is plenty.

Can I work out my inseam from my height?

Not reliably: two people of the same height can have legs several centimetres apart. That’s why the bike size calculator asks for it, and uses height alone only when you leave it blank.

Do I measure the same way for a mountain bike?

Yes. The inseam is your body, not the bike. Each chart then uses it its own way: × 0.665 for a road frame in cm, × 0.226 for a mountain bike seat tube in inches.