What Size Bike Do I Need?: Ultimate Bike Sizing Guide

by Bryan Ray | Last Updated: August 21, 2020

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What Size Bike Do I Need

I recently bought a brand new bike online after months and months of research. The end result was FAR from what I expected. Here’s what happened.

I googled the question ‘What size bike do I need?’ and ‘What’s the best bike for me?’. I took the advice of a few different websites and ordered my bike.

When it finally arrived and I took it for a spin…

IT. WAS. AWFUL. I was crushed. This was the most uncomfortable bike I’d ever ridden. My back ached, my knees burned and I was completely unhappy with the experience.

I purchased the wrong size bike!

The bike didn’t adjustments in different areas to help fit it to my body type. But, the frame was completely the wrong size for me. I learned that there is a huge difference between bike SIZE and bike FIT.

Here is the perfect guide to help you avoid this experience when buying your next bike!

Bike Sizing Chart For Men

Bike sizing chart men

What Size Bike Do I Need?

Like I said before, bike size is very different from bike fit. You want to start by selecting the correct size and then you can drill down into the specific fit.

Different brands will have different sizing specifications.  So be sure to read the fine print on the website, or in store if you’re at a local bike shop.

The first thing you need to focus on is the size of your frame. The finer adjustments of saddle height, handlebars, etc, will come later in the process.

You need to get the frame size correct first, and that takes a little bit of digging.

Some websites offer online calculators and other resources to help you make these decisions.

But, if you want to know the specifics about each measurement and what it means, keep reading. This will help you make a more informed decision.

BIke frame

The Three Elements of Bike Frame Sizing

Many cyclists make the mistake of thinking that the only important measurement in bike sizing is your height.

But, it’s not  that simple…

There are several measurements that go into the sizing of different types of bike frames.

Some manufacturers label their bike frames in small, medium and large. But, others use a specific number, which generally ranges from 48-62.

This number represents the numbers of centimeters from the center of the bracket (where the pedals connect) up to the top of the seat tube where the saddle post is inserted.

Since manufacturers are all different in their sizing method, your best bet is to measure these three elements of the frame:

These measurements are internationally recognized. This makes comparing different frames much easier.

You can see the difference between reach and stack measurements on a variety of brands. The reach and stack in particular will change the way the bike feels when you ride.

How Do I Choose the Correct Reach and Stack?

You will need to choose the reach and stack of your bike based on a lot of different things. Luckily, the bike industry understands these variables and has some basic parameters in place.

First things first, though: what type of riding will you be doing?

Bike frame geometry is not only varied by manufacturer and brand, but also by the intended use of the bike.

For example, racing bikes such as those ridden by the athletes in the Tour de France tend to have a very long reach and a lower stack. This allows the riders to stay low on the bike and be more aerodynamic.

A mountain bike will have a reach that is shorter and a stack that is higher. This lets the rider sit in a more upright position. This is better for comfort if the rider will be on the bike for a long period of time, but not racing for time.

Other than the type of riding you will be doing, another consideration will be your own fitness level. You want to consider the flexibility of your hamstrings, back and glutes.

If you are not very flexible, you will want your reach to be a little bit shorter to avoid strains and injuries. You will also be more comfortable.

Other things to consider for the reach and stack is the length of your arms, legs and torso. If you don’t struggle with flexibility, but your arms are short, you might have to choose a frame with a shorter reach.

Same thing goes with the stack. If you have short legs, you’ll need a shorter stack.

**Pro Tip: Different manufacturers usually have a sport frame and a race frame. If you’re not sure which one to choose, try this simple test. Bend over and try to touch your toes. If you can touch them, you’ll do fine on a race bike. If not, go with the sport frame.

How Do I Choose the Correct Height?

If you’re standing over the bike, you want the top tube to be low enough that it doesn’t touch your body. This is not only a comfort factor, but also a safety issue.

If you’re on the road and need to jump off quickly. A really high top tube will not allow you to do that.

The height is going to be a combination of the seat tube length, the size of the wheels and the saddle height.

Most bike frames come with an adjustable saddle. So that’s not as critical as the seat tube measurement and the size of the wheels.

Before shopping, you can do a simple measurement of your inseam and then go from there. Your inseam is the length from the bottom of your foot to the top of the inside of your thigh (your groin area).

Once you have this measurement, you can look at the specifications for different bikes online. Or in the store to make sure you choose one that will be comfortable for you.

Seat Tube Length

The seat tube length is the distance between the center of the bottom bracket to the top of the seat tube.

The seat tube is where the saddle stem inserts into the frame. This measurement will give you an idea of how tall the bike it.

But, this measurement does NOT take into consideration how tall the tires are. Although the tires are interchangeable to some degree, you still want to take them into the height consideration.

Wheels

Generally, wheels are measured by the diameter, or a straight line across the widest point of the circle. More often than not, they are measured in inches while the frame is measured in centimeters.

You might have to do some simple math and convert one to the other to get the full height of the bike, including wheels.

Different types of bikes have different wheel sizes, so keep that in mind. Mountain bikes generally have smaller wheels because they endure more bumps and impact than road bikes.

Road bikes are larger in diameter, but thinner in width. This allows the bike to glide over the road at a faster pace than the smaller, fatter wheels of a mountain bike.

If you’re shopping online, most bike manufacturers will list the height of the bike with these two measurements (seat tube length and wheel height) already combined.

But, I recommend that you read the fine print. Be sure to review the specifications to make sure that you’re getting an accurate account of how the bike will fit you.

bike sizing chart women

How Do I Choose the Correct Size for A Women’s Bike?

Just like men’s bikes, it’s important for women to choose the right size frame. Different types of bikes will have different frame sizes and measurements.

The first thing you need to do is figure out what type of bike you want. Do you want a racing bike, a mountain bike, or something in between like a hybrid?

You also need to choose whether you want a women’s bike or a unisex bike. This is a matter of personal preference and there is no right or wrong answer.

Just know that the bike geometry of a unisex bike will be different than that of a women’s bike.

Once you pick your style, choosing the correct size will be important to make sure you can adjust it to fit properly.

Keep in mind that if you buy the wrong size frame, it will be impossible to get a good fit. Even if you adjust the bike completely.

Most bike frames will be congruent with the height of the rider, but those sizes are different from style to style.

Racing bikes will be very different from mountain bikes. That’s why it’s so important to know what type of riding you’ll be doing before choosing a size and a frame.

All the measurements we discussed in this article apply to women’s bikes, as they do to men’s bikes. You need to figure out your inseam  to choose the right bike height. You also need to check your flexibility to determine how long or short your reach should be.

Since each style of bike is so different from a sizing perspective. I would look at some sizing charts for different bikes.

When in doubt, go to your local bike shop and get on a few different bikes until you find the size that you’re comfortable with. Even if you’re going to buy online, this will still help you narrow down your options.

How Do I Choose the Correct Size for a Children’s Bike?

Children’s bikes are much different than men’s or women’s bikes and for good reason. Your child is likely still growing, so it’s possible that you will be upgrading or changing them way more. Second, safety is extremely important for a child’s bike, for obvious reasons!

Most kid’s bike sizes are determined by the wheel size. Unlike adult bikes that have tons of adjustments and ways to fine-tune them, kid’s bikes are pretty simple. You base the bike size on your child’s height and that’s it.

Some manufacturers offer more advanced sizing options for kid’s bikes. So you don’t have to buy a new one every time your child grows a few inches.

I  recommend looking into these options if you want your child to keep riding. It might more expensive on the front end, but the bike will last a lot longer because your child won’t outgrow it quickly.

Elements of Bike Fit

After you’ve gone through the steps of figuring out your specific bike frame size, it’s time to take the fit into consideration.

The fit of the bike is comprised of all the small fine-tuning that you can do to various elements of the bike.

Saddle Height

Let’s start with saddle height because it is one of the most important elements of bike fit. Once you’ve chosen the correct size frame, you want to consider the height of the saddle. Here is a simple, step-by-step process to help you figure out your saddle setting.

This simple exercise will help you to setup your bike for the most comfortable ride. You can’t do this before purchasing the bike if you’re shopping online.

But if you buy a bike with an adjustable saddle height and you choose the right frame, you should be fine. Keep doing this and adjusting the saddle height until you find what works.

Reach Adjustments

Reach adjustments can be a little trickier, but are definitely possible. If you purchased a bike with an adjustable stem, you’re in luck!

You will need an Allen wrench to make these adjustments, so be sure to have one in the right size before you begin.

Adjusting Your Reach with the Stem

Just like in the adjustment of the saddle, you will want to be next to a wall or banister to help you balance while you decide your reach adjustment.

Unless you have an upright bike stand that allows you to sit on it while it’s standing up straight. There are a few ways to adjust your reach, so let’s start with the handlebars.

Here’s how to adjust your reach by changing the height of the stem, which is where your handlebars move up and down.

When you’re in riding position, the angle between your torso and your hips should be about 40-45 degrees.

The angle between your arms and torso should be about 80-90 degrees. If this is all way too much math, just go with what feels comfortable.

It may take you a couple of rides around the block to  figure out what’s going to work for you. But, these basic principles will help you get close to the perfect setup before your first ride.

Then you can adjust from there. If you take a few longer test rides, you will start to notice if your positioning is going to cause any aches or pains in your back, shoulders, hips or elsewhere.

Adjusting Your Reach with the Saddle

The other way to slightly adjust your reach is by moving the saddle forward or back. We already talked how to adjust the height of the saddle. Which is more about fitting the bike to your height than to your reach.

When adjusting the saddle for reach purposes, you will be moving either forward toward the handlebars or backward away from the handlebars.

You will need an Allen wrench or other tool for this adjusment, as well. Some bikes come with specialized tools just for this purpose.

Not all bikes have this option, and it is a less desirable way to adjust your reach. If you have to adjust the seat forward or back more than a few centimeters, you probably have the wrong size frame.

But try the adjustments first before you give up on the bike.

Saddle Tilt

Another fine-tuning change you can make is the tilt of your saddle. Different riders have different preferences for how they sit on the seat. So many bikes will come with an adjustment for this.

You want to be able to comfortably sit on the bike without feeling like you’re sliding off the seat.

Depending on the bike you purchased and the tools that came with it, you may need a special key for this.

Before I adjust my bike I ride the bike around the block a couple times. This gives me enough time to figure out exactly how much I want to tilt the saddle forward or back.

Summary

Choosing the right size bike is will help you avoid injury. Also, you can ride for long periods of time without discomfort.

Remember that the most important factor in your bike fit is the size of the frame. If you get the right size frame, all the other factors will be simple to adjust.

Remember my horror story from the beginning? If you get the wrong size frame, you’re in for some serious heartache.

It pays to do the research and spend the time finding exactly the right frame size for you.

Happy riding!

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