The inseam is the length from your crotch to the bottom of your leg. It’s expressed in either inch (North America) or centimeters (Europe) depending on where you’re located.
Sometimes, it’s also referred to as the inside leg measurement.
Why is inseam measurement important for bike sizing?
Inseam is a good starting point to help you determine the correct bike size.
There are also other measurements to consider such as stack and reach. Bikes come in many sizes and riding the correct size is important for your comfort, enjoyment, injury prevention, and safety on the road.
The inseam measurement is used together with the standover height (S.O. height). The standover height is the distance from the mid-point of the top tube to the ground. It’s usually expressed in millimeters.
Each bike model has its own size chart (also known as a geometry chart) and you can find the standover height from there.
The ideal bike size is where the standover height is around 1.5” to 2” (38.1 to 50.1mm) lesser than your inseam. This provides a clearance for you to quickly hop on and off the bike when needed without the top tube getting in your way.
How to measure your inseam at home
What you need
- A large book, preferably around A4 size and 1” thick
- Measuring tape
Step by step instructions
- Put on your usual cycling bibs.
- Remove your shoes and socks.
- Find a flat and hard surface at home.
- Stand flat-footed with your back against a wall, and your feet around 6” apart. Make sure your heel touches the wall.
- Place the book in between your thighs. Raise it up until it’s snug against your crotch.
- Make sure the book is parallel to the ground. You can ask someone to help you with this.
- Hold the book in place and slowly move forward and away from the book.
- Use the pen and make a mark where the book meets the wall.
- Measure the distance from the ground to the mark you’ve just made. This is your inseam measurement.