How to Measure a Bike – 3 Easy Checks to See if a Bike Fits You

Updated June 27th, 2023

Buying bikes online has become much more common these days.  Many popular e-Bike brands only sell direct to consumer. How do you know which size bike to buy? What if you are looking at a used bike? Will it fit you? Following the bike manufacturer’s size chart is a good place to start. If you are buying used there may be no size chart to go off of. A little understanding of how to measure a bike frame can help you choose the right bike size for you.

Why does bike size matter?

A correctly sized bike will be more enjoyable to ride. It will feel better and be easier to pedal. A lot of e-bike companies sell more or less one size fits all bikes with 1 available frame size. They stretch the numbers a bit to try and say it will fit a wide range of riders. It may not be a great fit for anyone at the large and small end of their recommended size range. It isn’t as bad as a pedal bike since the motor is doing a lot of the work for you. A correctly sized e-bike will go farther since you can pedal more efficiently. It will handle better because you fit the frame better.

What are the consequences of a bike that is too big or too small?

A bike that is too small will feel crouched and uncomfortable to pedal. Your legs will get tired quickly because your legs don’t extend far enough when pedaling. The bike will feel twitchy because the handlebar is too close to you and the wheelbase is too short for your size.

A bike that is too large will make you feel like you’re bending over too far to reach the handlebar. You can have some painful experiences if you dismount too quickly and land your crotch on the top tube. The bike will feel difficult to turn because you are reaching too far for the handlebars. You may not be able to pedal efficiently because your leg needs to extend too much to reach the pedals on the downstroke.

The easiest way to figure out what size bike will fit you is to take a look at the bike manufacturer’s sizing chart. This will tell you the height range that their bike sizes correspond to. Some size charts will give you an inseam length as well. These are only estimates. 2 people of the same height can have shorter or longer legs and shorter or longer arms. It gets you in the ballpark for the correct size.

If you are on the border between sizes, the best thing to do is try riding the bikes and see which size feels better. I am on the border between medium and large. I always fit size large for Specialized brand bikes. I fit size medium for Giant bikes. If you are on the border between sizes there is no hard rule for whether going up or down will be better. If you can’t try out a bike you should contact the bike manufacturer and tell them your height and inseam length and see if they have a recommendation for which way to go.

Bike Manufacturer Sizing

Bike manufacturers specify bike sizes in several different ways. The most common ways are with standard T-Shirt sizing or seat tube length.

T-Shirt Sizing

A lot of bike manufacturers refer to their bike sizes as XS, S, M, L, or XL.  You can find some XXS and XXL frames out there as well. This is easier than trying to give the size as a measurement in inches because there is so much variation in seat tube lengths.

Seat Tube Length Measurement

Bike manufacturers refer to the length of the seat tube as the size of the bike. This is the distance from the bottom bracket (crank pivot point) to the top of the seat tube. 

This dimension gets muddied up because a lot of seat tubes are curved. The seat tube can be shorter or longer depending on how angled the top tube of the frame is. 

The seat tube will give you a rough size measurement for the bike but that is about as far as it gets.

What about women’s bike sizing?

Bikes are measured the same way for both women and men. The old days of a women’s bike always being a step thru-frame are long gone. Most bikes these days are unisex. Step-thru bikes are just referred to as step-thru frame bikes instead of women’s bikes. If you are a woman you measure yourself the same way and use the same size chart.

How to measure yourself

There are 2 important measurements to take before you start looking up bike size charts.  Your height and inseam length

Height

Measure from the ground to the top of your head. 

Inseam

To measure your inseam stand against a wall with your back touching the wall. Hold a book between your legs with the book up against your crotch. Measure from the top of the book to the ground. This will tell you how long your inseam or leg length is. Some bike brands will include inseam measurements in their sizing information. 

Mountain Bike Size Chart

Road Bike Size Chart

What about other bike types?

Hybrid Bike

Hybrid bikes tend to be similar to mountain bikes. They have frames and geometry similar to recreational mountain bikes with slightly thinner, less beefy tires. Most have flat or bent handlebars similar to a mountain bike. They have a more upright riding position.

Gravel Bike

Gravel bikes tend to size similar to road bikes. They are more or less a beefy road bike frame with thicker tires on it. They still have drop bars and a road riding position.

Electric Bike

Electric bikes can be setup like any other type of bike. There can be electric mountain bikes and electric road bikes. Use the sizing guidance for the type of bike the electric bike your looking at is. If it is an electric mountain bike then look at a mountain bike size chart.

How to measure a bike frame

There are a lot of bike frame size measurements such as reach, stack, seat tube length, head tube angle, chain stay length, and so on. The 3 most important measurements for figuring out if a bike will fit you are the seat tube length, stack height, and reach. These will tell you how big a bike is and whether it has a more performance oriented or more upright riding position. 

Seat Tube Length

The seat tube length is the length from the bottom bracket to the top of the seat tube. 

Stack Height

The stack height is the vertical distance from the center of the bottom bracket to the top of the head tube. A bike with a higher stack height will have a more upright riding position. The handlebar will be higher relative to the pedals. A low stack height will give a more performance oriented bent over riding position.

Reach

Reach is the horizontal distance between the bottom bracket and top of the head tube. A larger reach means a bike has a more leaned over riding position. A shorter reach will give a more upright riding position. 

What do these measurements mean? A recreational bike will have a taller stack height and shorter reach for the same seat tube length compared to a racing bike. This will give a more comfortable upright riding position. 

How to tell if a bike fits you.  3 things to check

1 – Swing your leg over the bike and stand over it. There should be 1 to 2 inches of gap between the bike frame top tube and your crotch. If there is less the bike is too big for you. You run the risk of hitting the top tube in a painful way if you get off the bike too quickly. If the gap is larger the frame is probably too small for you and you will have an uncomfortable, too crouched riding position.

2 – Get on the bike seat and check how extended your leg is with the pedal in the down position. When the pedal is at 6 o’clock and your butt is on the seat, your knee should have a slight bend around 10 to 15 degrees. If your knee is bent too much, adjust your seat higher. If your knee is bent too much, pedaling will not feel good. You will need to use more effort because your leg is not extending enough. Your knees will get sore also.

3 – Ride the bike and see how it feels. Do you feel like you are reaching too far forward for the handlebars?  Do they feel too close. You can adjust the fore/aft position of the saddle to give yourself more or less reach. If you feel like you are reaching too far down for the handlebar you can sometimes add more spacers and lift the bar up a little. 

Bike wheel size

Bikes come in a lot of different wheel sizes. Mountain bikes may have 26inch, 27.5, or 29 inch wheels. Road bikes have 700mm or 650mm wheels. Folding bikes and BMX bikes have 20 inch wheels. In general, a larger wheel size will give a smoother and more efficient ride. Smaller wheels will give a rougher ride and not roll as well. Smaller wheels are more nimble and turn quicker. They can make a bike easier to store. 

How does wheel size affect bike sizing?

There isn’t really any connection between wheel size and bike size for adult bikes. There are XXS 29inch wheel mountain bikes out there.  There are XXL size mountain bikes with 26 inch wheels. Bike designers are pretty good at designing frames and suspensions around different wheel sizes. It is more important to choose a wheel size that will give you the ride you are looking for. 

Folding bikes use small wheel size to make the folded bike more compact. There is no other reason for putting smaller 20 inch wheels on them. BMX bikes tend to have 20 inch wheels. They perform best for the type of riding done on a BMX course.

Bike Size FAQ

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