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downhill road biking

How to size your next Bike 

You’re buying a bike?! Let us be the first to wish you congratulations. Bike purchasing is one of the fastest tickets to happiness, in our opinion.

Of course, especially if you’re buying the bike online, you’ll want to choose the size carefully. This is no small matter: the wrong size of bike frame can lead to all sorts of riding discomfort, no matter how much you adjust the bike’s components. You’ve got to start with the right frame size for your body—no “ifs”, “ands,” or “buts” about it. Frames are typically sized in Small, Medium, and Large, with some XS and XL outliers available too.

It’s a bit of an art to select the right frame size, and unfortunately, most brands are a little different from one another. So do all the online research you can about your intended brand or bike: what are people saying about the fit? What do people with similar body sizes and types to you say about the frame that worked for them?

bike graphic

There are a few really strong pointers you can start with. Here they are: 

  • Measure your inseam.
    Your inseam length is the main starting point bike frame sizing charts use. Don’t just depend upon your typical pant-leg length—you’ve gotta be more accurate than that. The simplest way to do it is to grab a tape measure, take off your shoes, nestle a hardcover book as high as you can between your thighs, and then measure the distance from the top of the book to the floor.

  • Find the bike sizing chart for the brand you’re interested in online.
    Not only is every brand different, but there are differences between what you’ll want for a mountain bike versus a road bike. So don’t just search “Specialized bike size chart”—hone in on their road bike chart or mountain bike chart, respectively.

We do have some good brand-agnostic charts here that you can look at below—which could be handy if you can’t easily find a size chart for your intended brand.

road bike frame chart
bike frame size chart

There are a few additional details to watch for: You’ll want to find out the bike’s “frame standover height,” which can vary depending whether the frame’ top tube is parallel to the ground or if it slants downward from the handlebars to the seat post. If you measure your inseam with bike shoes on, you’ll want to make sure the top tube would be an inch below your crotch (for a road bike) or two-plus inches below your crotch (for a mountain bike).

For road bikes in particular, it’s also helpful to know the “effective top tube length” (ETT). A bike tech can help you run the numbers, but basically, you want a top tube that puts the right distance between you and your handlebars. If your torso can stretch forward at a 45-degree angle and your arms can extend downward at a 90-degree angle from your torso, you’re in great shape to cover serious mileage comfortably.

Keep in mind that women and men often have different body proportions, so there could be a big difference in comfort if you get a gender-specific frame.

Once you have your bike, you can tweak all the components for final fine-tuning—adjusting the seat height, seat fore/aft position, saddle tilt, and other details for a comfortable feel.

Have a ball on your bike-shopping journey. The only thing more fun than choosing a bike is riding it. That, we guarantee, will be awesome.

Beth LopezBeth Lopez is a seasoned writer and creative director who loves to tell tales of adventure and discovery—and finds writing a powerful way to give a voice to people, causes, and places. Beth runs amok in the Wasatch mountains when untethered from her computer. She believes there’s no such thing as a bad ski day and considers animals her favorite people. Don’t tell her mother about her Instagram mountaineering photos.