There are three crucial things to get right when you buy a bike. One of these is your bike frame size. If you get this wrong, the bike will NEVER be right for you. This bike frame size guide will show you how to determine your correct bike frame size. This guide also includes information on choosing the right kid’s bike frame size, and advice on whether to choose a women specific bike.
These are the three crucial things to get right when you buy a bike:
- Buy the right kind of bike for the type of cycling you plan to do – here’s a guide to the different kinds of bikes.
- Buy your bike from a bike shop, or buy a good bike used (get advice on buying used bikes here) – but don’t buy a bike from a department store. These bikes have poor components and are often assembled by people with no bike knowledge.
- Buy the right size bike frame – read this post!
Related: 7 Great Bikes You Can Buy from Amazon
You can change all the other components, but you are stuck with the kind of bike and the bike frame size. If you make the wrong choices with these, you will end up having to sell the bike and start again. Or you will just find cycling unsafe and uncomfortable. You may develop cycling knee pain – and most likely you will quit cycling and never get to experience the amazing health benefits of cycling.
Bike frame sizes are based on the height of the bike, measuring the length of the seat post tube – the part of the bike that the seat post (and saddle) slide into. This measurement is given in metric (cm) for road bikes, and imperial (inches) for mountain bikes.
Here’s a short video showing how to measure bike frame size.
I have made the mistake of buying a bike that was too big, just because I loved the look of the bike. Big mistake! I could never get completely comfortable on the bike, and eventually I had no choice but to sell it. I am embarrassed to admit that I actually made this mistake twice! (I’m just a sucker for a pretty bike.) Buying the wrong size bike is an expensive, time-wasting mistake – and it can even be dangerous.
If your bike has the right frame size, you will be able to comfortably stand over the cross bar. You will be able to stop safely, rather than having to fall helplessly sideways until your foot hits the ground!
If your bike is too small, your knees and back may start to hurt, and you won’t be able to use your leg power efficiently (plus you may look funny – a bit like a penguin!).
Height, Inseam Length and Reach – the Three Vital Measurements to determine the bike frame size
Height and Inseam Length
The two most important measurements to know are your height, and your inseam length (the distance from your crotch to the end of your pant leg). Of these two lengths (height and inseam), inseam is the most important.
The reason the inseam length is the most important is because it determines your stand-over height. For example, if a bike has a stand-over height of 27 inches, and you have an inseam length of 29 inches, you will be able to stand over the bike, and the cross bar will not hurt you if you have to stop suddenly. (Obviously this is less important with step-through style bikes that do not have a cross bar.) Also, this bit of clearance will enable you to safely and easily hop off the bike when you need to.
For road bikes you need to have about 1 to 3 inches of distance between the bar and your crotch; for mountain bikes it is safer to have an inch or two more.
Your Reach – Do you Have a Good Ape Index?
Your reach measurement becomes important if your height and inseam measurements put you in between sizes. In that case, use your reach measurement to decide.
You need to know if you have a long or short reach, which means you need to find out your “ape index” (which is your arm span compared to your height).
- If you have a positive ape index (your arm span is greater than your height) then you have a long reach and you should probably go for the larger of the sizes.
- If you have a negative ape index (your height is greater than your arm span) then you have a short reach and you should probably go for the smaller of the sizes.
For example, say you have an arm span of 160 cm and a height of 160 cm. This would mean your arm span is exactly the same as your height. So you have an ape index of 1, and therefore an average reach. However, if your arms are shorter, you have a short reach, so if you are between frame sizes, go for the smaller frame size.
Two Different Bike Frame Size Systems
Just to make it a little more challenging, there are two different bike-sizing systems. There’s one system for road bikes, and then a different one for mountain bikes and hybrid bikes. Sizes are given in metric (cm) for road bikes, and imperial (inches) for mountain bikes.
You can figure out your bike frame size with the Bike Frame Size Guides below
Even with the right frame size, if you are planning to do a lot of cycling, you should still get your bike fine-tuned with a professional bike fitting, if you can afford it. If you are buying a new bike, try to find a bike shop that offers some help with bike fitting. Some of them are especially good with this, and will give you a professional level of help. (Many of the smaller bike shops cannot afford this, however.) Getting a well fitting bike will protect you against back pain or cycling knee pain.
Do You Need a Women’s Specific Bike?
On average, women tend to have longer legs and shorter torsos than men of equivalent height. Women specific bikes offer smaller frame sizes, shorter top tubes, narrower handlebars, female specific saddles and smaller brake handles.
However, you are unique, and a women specific bike may not be right for you, even if you are a woman. The bike you choose should be the perfect fit for you individually, regardless of gender.
If you are shorter than about 5 ft 5 in (165 cm) or have felt too stretched out on unisex bikes before, you may be more suited to a women specific bike. Try them out and see what works for you. I have known women who have been absolutely ecstatic on riding their first women specific bike, because for the first time they felt like the bike really fitted them. On the other hand, other women find no benefit in them.
Also, bear in mind that if you are a short man, a woman specific bike may be right for you. No one needs to know! The reality is that the average male height in some countries is shorter than the average female height in others. For example, average male height in Indonesia is 5 ft 2 in, while average female height in The Netherlands is 5 ft 7 in (must be all that cycling that makes them grow so tall and strong)! So obviously, we cannot really generalize too much about this matter. Everyone is unique.
How to Choose the Correct Size Kid’s Bike
Kid’s bikes are measured and sized differently. Often they are categorized in age ranges and wheel sizes, as you can see from the table. But keep these points in mind:
- Don’t rely on an age range to pick a bike size for your child. There are tremendous variations based on individual differences. Just as with gender, age does not necessarily predict height.
- Height and inside leg measurement remain the key factors. Keep this in mind and make sure your child can comfortably stand over his or her bike. This is especially important for safety for kid’s bikes – they need to be able to stop safely, and get off safely. Don’t put them off bikes for life by making their early experiences scary. Which brings us to the next point:
- Do not buy a bike that is a bit bigger, thinking your child can grow into it! The bike needs to fit from the get-go, so that your child does not get hurt or frightened. Unlike a jacket, a child can actually fall off a bike, so buying big is not a good idea. You may be able to extend the useful life of your child’s bike by raising the saddle when he or she grows. But you must have the right frame size to begin with.
Note: The tables showing how to pick the right frame size are extracted from my Bike Buyer’s Guide (aka How to Buy Used Bikes Online). Subscribe to this blog to get a free download of the entire book!
All of the above should be used as a guide. There is no substitute for trying out the bike and taking it for a good test run. Good luck with finding your perfect bike!
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