Bike Size Chart: What Size Bike Do I Need?

Before researching which bike to buy, you need to know what’s the right size bike for you. A properly sized bike will perform as you want it and be easier and more comfortable to handle. It’s always better to try out a bike in person at a bike shop, where you can also have it fit precisely to your body type and how you like to ride.

If you don’t have access to a bike shop, though, you’ll need take a couple of measurements — height and inseam — to get a general idea of the right size bike for you. Road bikes and mountain bikes have slightly different frames so calculating the measurements is a little different. But overall it’s a very easy process.

Once you get the bike, however, you’ll probably need to make adjustments to accommodate your torso length, arm length, and lower-leg length. Unfortunately, there is no industry standard for bike sizing, and sizing often varies from one manufacturer to another.

Choosing the style of bike — mountain, road, hybrid — is your first step before measuring since their frames are somewhat different in design. How and where you want to ride your bike is a crucial factor in determining the right size for you.

Bike frame terminology

When researching the type of bike you want to buy, you’ll see several terms of which you need to be aware to ensure that you purchase a properly sized bike.

Top tube

This is the horizontal tube that runs from the seat post to the handlebars. The length of the top tube will determine your reach to the handlebars and your posture while you’re riding. When you see a bike frame measurement for a road bike, it is referring to the length of the top tube and not the actually frame itself. The industry standard for road bikes is to measure the top tube in centimeters.

Bike frame size

Mountain-bike frames are measured in inches, using a vertical measurement from the middle of the pedal crank to the top of the seat tube. Some manufacturers also provide sizing charts that are based on a person’s height, such as x-small, small, medium, large, etc.

Standover height

An important measurement is standover height, which, for road bikes is 2″ higher than your inseam and for mountain or commuter bikes is 3″-4″ higher than your inseam. This additional height allows for safe and comfortable standing over your bike when you’ve dismounted. 

However, these sizes are different for different styles of bikes, so it’s not a one-size-fits-all scenario. For example, a road-bike’s top tube that measures 54 centimeters is usually considered to be a medium, but in some cases, it may be labeled as a small, depending on the bike’s model and manufacturer.

So although it may seem easiest to choose a bike size like you would choose clothing size, it won’t necessarily be accurate, which is why you should take certain measurements to ensure a preliminary good fit.

But figuring out the right size bike for you isn’t difficult and quite a lot easier than properly fitting a bike helmet.

Fitting example for road bikes

Road bike frames are based on the length of the top tube. It’s quite simple to calculate the size that is recommended for people of different heights. But because road bike frames are listed in centimeters, you’ll need to convert your measurement from inches to centimeters.

1. First, measure your inseam with a measuring tape from floor to your crotch. In this example, a 6’1″ man has a 34″ inseam.
2. Convert the inseam measurement to centimeters. You can use an online calculator or multiple the inches by 2.54. Our example’s inseam converted from inches to centimeters is 86.86 centimeters.
3. Next, multiply the converted inseam by 0.67 to calculate the top tube length. (This decimal fraction is an industry standard for road bikes.) For our 6’1″ man, it equals 57.86 centimeters. So based on our chart below, he would purchase a road bike between 58-60 centimeters.

Bear in mind that this is a general guideline and other factors can be involved, such as arm length, torso length, and lower leg length, which come into play when you are actually sitting on the bike you’ve bought.

Whatever size bike you decide to buy, one of our top picks for the best bike rack will support it securely in your garage or home.

Road bike sizing chart

A road bike is designed for smooth and fast riding on paved areas. It has a lower-placed handlebar to encourage a forward-leaning position. A road bike’s frame is rigid, which transfers the power of your pedaling directly to the wheels. Road bikes are always measured in centimeters because it allows for a more precise fitting to your body.

Fitting example for mountain bikes

1. First, measure your inseam with a measuring tape from floor to your crotch. Again, for this example, our 6’1″ man has a 34″ inseam.
2. Since mountain bike frames are always measured in inches, simply multiply your inseam measurement by .65 (an industry standard for mountain bikes), which in our example for a 34″ inseam equals 22.1″, which is the bike frame height figure.
3. According to our chart below, a mountain bike with a 22″ frame height (or extra large) is a good choice for our 6’1″ man to consider purchasing.

Mountain bike sizing chart

A mountain bike is designed for control and stability over rugged terrain. Its frame is more upright than a road bike and allows for better visibility for the rider. A mountain bike’s frame often has forward or full suspension to absorb bumps. The industry standard is to measure a mountain bike in inches.

Kids bike sizing chart

When buying a kids bike, it’s important to remember that a child will soon outgrow it. Experts recommend buying a bike that’s slightly larger, which will allow for the child’s growth. The child’s height and inseam measurements (in inches) are necessary for ensuring the bike is a good fit. Sizes for kids bikes are grouped together by wheel size; for example, 12″, 14″, 16″, etc.

Final thoughts

Every bicycle expert strongly recommends sizing a bike to fit your body on the actual bike you want to purchase. Even if you use our sizing charts to buy a bike online, it’s worth your while to find a bike shop to make adjustments because all bikes will need to be adjusted to ensure that you have an enjoyable and comfortable ride.

Our guides, however, are a good starting point, and if you’ve measured yourself correctly, it’s likely that you’ll be able to make the adjustments to your new bike yourself.

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Gene Gerrard, Writer

Gene has written about a wide variety of topics for too many years to count. He's been a professional chef, cooking-appliance demonstrator, playwright, director, editor of accountancy and bank-rating books, Houdini expert and dog lover (still is). When he's not writing for Your Best Digs, he's performing as a magician at the Magic Castle in Hollywood.