Bikes are complicated to size perfectly. Many bike manufacturers suggest that you use your inseam measurement as a starting point when determining what size frame you should buy and how you should set up your bike. Your inseam measurement alone won’t get you a perfect bike fit, but it’s a valuable tool that can help start you in the right ballpark.
The inseam height of an average person is calculated by the height of the rider divided by 2.18-2.3. A 5’11” (180 cm) tall person’s inseam height is typically 30.7″ – 32.7″ (78-83 cm). Males and females tend to have similar height/inseam length proportions, but taller people usually have longer legs. Genetics of the individual also plays a part in your bodily proportions.
If you’re wondering what your inseam length is, how you can measure it, or why it’s so important, you’re in the right place. We’ll go over everything you need to know about what this measurement is, why it’s important, and what happens when you choose a frame that’s too big or too small. With all of this knowledge, you’ll be able to look at a bike sizing chart and get a feel for which bikes are just the right size for you and your body.
Before we jump right into it, here’s a quick table that helps you get a general overview.
|Height in ft in||Average min inseam||Average max inseam|
|Height in cm||Average min inseam||Average max inseam|
|150 cm||65 cm||69 cm|
|155 cm||67 cm||71 cm|
|160 cm||70 cm||73 cm|
|165 cm||72 cm||76 cm|
|170 cm||74 cm||78 cm|
|175 cm||76 cm||80 cm|
|180 cm||78 cm||83 cm|
|185 cm||80 cm||85 cm|
|190 cm||83 cm||87 cm|
|195 cm||85 cm||89 cm|
|200 cm||87 cm||92 cm|
What Is Inseam Height?
Your inseam is a measurement of the length of your leg. While you’re standing, your inseam runs from your foot up the inside of your leg to your pubic bone. It’s a common measurement for both clothing and bikes that’s very useful due to the differences in body proportions.
Why We Use Inseam Height
Different people are sized differently. In addition to our varied heights and weights, people have different arm, torso, and leg lengths. These measurements can be fairly disproportionate to your height. It’s not unheard of for people who are 6″ or more apart in height to have similar inseams or arm lengths.
This vast discrepancy means that the best way to make sure a bike is the right size for your leg length is to actually measure your leg length. For casual cyclists, leg length is probably the most important measurement, as it gives you a good idea of how high you’ll want the seat and the top tube on the bike. The longer your legs, the higher you’ll want to bring the seat, and the higher the top tube can be without causing any issues.
If you’re a more serious cyclist, you’ll probably want to consider a few other variables, such as
- The length of your arms,
- the length of your torso, and
- how flexible you are.
These factors will all have some effects on how your frame fits. Depending on the type of bike you have, your individual riding style, and how you set up your bike, you might find that these measurements will shift your ideal frame size a fair bit in either direction.
How Can I Measure My Inseam Height?
To measure your inseam height follow these simple steps:
- Stand straight against a wall not wearing footwear
- Take a book or another stiff rectangular object
- place it vertically between your legs with one side flat against the wall and
- lift it snugly against your pubic bone
- once you’ve got it positioned, keep the book against the wall and measure the distance between the top of the book and the ground.
Your goal here is to pull it against the flesh at the very border of your leg until it’s slightly uncomfortable. This ensures that you’re measuring the actual length of your leg and not anything else.
You can either measure your inseam height yourself by holding the book in place and stepping away to measure or by asking a second person to help.
For the best measurements, try to repeat this whole process two or three times and take the average. In many cases, you’ll wind up with a slightly different measurement with each repetition.
Repeating the measurement helps to remove variables from the equation and gives you the most accurate measurement of your body.
Typical Inseam Heights
Men and women have very similar average ratios of inseam length to height. This ratio varies slightly, but the factor that causes this discrepancy is average height, not gender (reference). Taller people tend to have longer legs and men tend to be taller than women.
The ratio of inseam length to height tends to be between 1:2.2 and 1:2.5. To estimate your inseam, take your height in inches and then divide by these numbers in turn.
If you know you’ve got shorter legs, it’s probably closer to the smaller number, while if you’re tall or you have longer legs, you’ll want to use the larger number as an estimate.
If you can, however, try to actually measure your inseam. All you’ll need is a tape measure and a book.
Bikes With The Wrong Size Frame
Generally speaking, it’s easier to ride a bike with a frame that’s slightly too small than a frame that’s too big.
Bike too small
A frame that’s too small will require that you jack the seat all the way up and have handlebars that are too low to the ground while being fairly close to your body horizontally.
This can cause balance issues and can lead to discomfort or stress injuries if the bike is significantly too small and you ride it a lot.
That said, professional bike fitters generally find that people wind up with bikes that are too big for them when they use size charts and personal experience. If you can, try to err on the side of getting a bike that’s very slightly too small.
Bike too big
When a bike frame is too big, a number of things start happening.
For starters, you’ll have trouble mounting and dismounting on many frames.
Bikes have a measurement called the standover height that describes how tall the top tube is. If the standover height is longer than your inseam, you won’t be able to stand over the top tube with your feet flat on the ground.
Even if the standover height is a few inches above your inseam, you’ll have issues mounting and dismounting on level terrain. Some frames have design features that alleviate this issue somewhat, but it’s definitely a thing you’ll notice on traditional hi-step bikes.
Second, the handlebars will be farther away from the seat. They’ll be higher than they should be on a properly sized bike, lifting your arms up, but you’ll have to stretch more than normal to reach them.
On a bike with low handlebars that are close to your body, this might not cause a huge issue, but on a cruiser that’s supposed to have high, far handlebars, you might have problems controlling the bike.
Finally, you’ll also probably have to ride the bike with the seat all the way down. Even with the seat as low as it will go, you might find that you have to straighten your legs too much to reach the bottom of the pedal stroke.
Just like with a bike that’s too small, these issues are often manageable for casual riding on weekends. The more you ride, however, the more likely you are to experience discomfort related to your bike being the wrong size.
Suggested reading: https://www.wheelies.co.uk/buying-guide/adult-bike-size-guide