Selecting a new bike is thrilling but can be quite daunting when you’re presented with the vital question: “What size bike do I need?” The most important factor when considering a new bike is to find the right frame size for you. A bike that is too big or too small can make for an uncomfortable ride and even cause long-term pain in your back, neck, and knees.
This ultimate guide is aimed at untangling the mystery of bicycle sizing. We will guide you toward methods that give the most accurate measure of your ideal bike frame size, plus options and factors to consider when purchasing a bike and charts that help you take the guesswork out of finding the right fit. Whether you are a new or an experienced cyclist, this data will help you feel comfortable and sure on the road.
The 2 Primary Aspects of Bicycle Sizing: Leg and Height
Although the overall height of your body is a good place to start, the single most important factor that puts the bike in an optimal riding position is your inside leg length, aka your inseam. This is because people have different leg-to-torso ratios. An accurate inseam measure helps to get you the right standover height — the gap between you and the bike’s top tube when you are standing with feet flat on the ground. This is crucial for safety as well as for comfort.
This is why we use your inseam in our Bike Frame Size Calculator — it gives better personalization than height by itself.
How to measure your inside leg (inseam)?
For the most accurate reading, you will want to take this measurement with care. You’ll want a friend to help you, but you can do it yourself.
You will need:
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A tape measure
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A big, heavy book or a spirit level
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A wall to stand against
Follow these simple steps:
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Prepare: Slip off your shoes and any thick pants you may be wearing. You’re probably best off wearing form-fitting cycling shorts or athletic gear. Stand with your feet shoulder-width apart, barefoot, with your back straight against the wall.
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1: Position the Book: Place the hardcover book between your legs, spine up.
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Exert Pressure: Then smoothly and somewhat forcefully slide the book upward until it's wedged against your crotch. It should approximate the pressure of sitting on a bike saddle. Be certain the spine of the book is horizontal and the book is parallel to the floor. For the most accurate result, a spirit level is best used here.
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Measure: Stand upright with the book against the wall between your legs. Have your friend measure the length from the top of the book’s spine straight down to the floor. If you’re by yourself, hold the spine of the book against the wall, then use the tape measure to measure the distance.
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Record the Measurement: Record the measurement in centimeters for the most precise calculations by bike manufacturers. This measurement is your inside leg length.
Understanding How Frames are Measured
Frame size may come in centimeters (54cm) or inches (18″), or even vague sizes such as Small (S), Medium (M), and Large (L). In general, the number indicates the length of the bike’s seat tube. But there are two standards by which to measure it:
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Center to Center (C-C): Measured from the center of the bottom bracket to the center of the top tube where it meets the seat tube.
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Center-to-Top (C-T): This is taken from the center of the bottom bracket to the top of the seat tube.
As you can see from the above, different countries use different standards, so it is important to know which standard a manufacturer uses as this can affect the size listed. But for this guide, and our calculator, we have you covered—the suggested dimensions are calculated to be generous with those space allowances in mind.
Bike Size Charts by Type of Bicycle
There is no one size that fits all, and the frame size will vary wildly depending on the style of bike you have. Every type of bike has a specific frame geometry developed for its purpose, and this directly affects how it fits the rider. Here, we walk you through what to think about when sizing four specific types of bikes.
Mountain Bike (MTB) Sizing Guide
Mountain biking calls for speed, control, and maneuverability over rough terrain. Their geometry is more stable, with a longer wheelbase and sometimes a dropped top tube. This slope results in more standover clearance to safely dismount or just for heading out to explore the trail.
And that's why mountain bike frames are measured differently, and a mountain bike feels smaller than a road bike for the same person. The size of the frame is usually measured in inches, although centimeters are also used. Although frame size is the first thing you’ll spend time determining, you should also think about adding a design aesthetic to the mix.
Here’s a helpful chart to get you in the right ballpark based on your total body height.
Road Bike Sizing Guide
Road bikes and their overgrown cousins, cyclocross bikes, are quick, efficient, and designed to ride on pavement or mixed surfaces. They are a bit more aggressive, and the rider is positioned a bit more "forward" versus "upright". This is accomplished through shorter chainstays, steeper tube angles, and a longer (relative) seat post than a mountain bike.
Therefore, for the same rider, the frame sizes are numerically bigger on road bikes. So someone who rides an 18-inch mountain bike would probably need around a 54 or 56 cm road bike. Sizing is almost always done in cm. Fit is key for road cycling because spending long hours on poorly-fitted bikes will take its toll on your backside if you’re not careful.
Use this chart merely as a picture of what you might look for in your new road bike frame size.
Trekking & Touring Bike Frame Sizing Chart
You could say the same for trekking or touring bikes, which are the marathon runners of the cycling world. They are designed for comfort, stability, and reliability (most commonly with panniers) over long distances. Their geometry is a mix between a road bike and a mountain bike, with a more relaxed, upright position to put less stress on the rider’s back and shoulders over daylong rides.
Even though they may have the same seat tube lengths as road bikes, they usually have a lower bottom bracket for stability and a longer wheelbase to provide a smooth ride and to prevent the heels from striking the rear panniers. Comfort is the top priority, so the fit should be less aggressive than a road bike but more efficient than a city bike.
Use this chart to determine what size you need for your next adventure.
City / Everyday Bike Frame Size Guide
City and everyday bikes (which are sometimes referred to as hybrid or commuter bikes) are built for comfort, utility, and visibility. The geometry is set up to make you sit fully upright. It offers an unobstructed view of traffic and doesn't stress the rider's back and neck. The fit is the loosest of all bike types; however, finding the right size is crucial for your stability and control as you’re commuting and tooling around.
Discover the best city bike size for you with the table.
FREQUENTLY ASKED QUESTIONS
Q) Will you fit on a MOTAN 750 when you are 5' 1"? A) Yes, the MOTAN 750 has been designed to fit riders who are from 5'4" to 6'6", but it really depends on your preference. If you want to be able to put your tippy-toes to the ground, you might want to test ride it to see if it's a good fit.
What About If You’re In Between Sizes?
The location of your measurements is often right between two frame sizes. If you end up choosing one or the other to be yours, let your riding style and the size of your body parts (your “ape index,” the proportion of your arm span to your height) guide you.
Here are the general rules of thumb:
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Select the smaller size for a more athletic ride. A smaller frame will also be a little lighter and stiffer. It's going to provide a more aggressive and nimble riding position; you're going to have a lower handlebar relative to the saddle. Racers and those who take their riding very seriously tend to like this option.
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If you prefer a more comfortable ride, pick the largest one. A bigger size will have a taller head tube so that your handlebars are also higher, making for a more leisurely, upright riding position. It's perfect for long days in the saddle and confident enough when it comes to easy cruising or for those whose perfect bike is the one that makes them feel comfortable in longer-distance cruising.
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If you have a long torso and long arms in proportion to your height, you might find yourself more comfy on the larger size. If your arms or torso are shorter, you will probably need one size smaller.
Final Thoughts: A Rule, But Not a Foolproof One
Bear in mind that the information and charts you see here, in addition to the results given by our calculator, are the special recommendation and very accurate advice we can offer. In most cases, they will get you to the perfect frame size or something very close to it.
But the right bike fit is also a subjective feel. Of course, the ultimate test is a test ride. If you can, sit on and pedal a bike before buying it to make sure it feels good. The right bike feels great to ride, and we want to help you get there with a bike that fits your preferences and body.