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Bike Sizing Guide

Bike Sizing Guide

Getting the right fit makes all the difference. This sizing page contains all the information you need (and a handy sizing calculator) to make sure you get the right size.

Bike size calculator

Your mountain bike size is:

Frame (inches): 16/17
Frame (size): Small / Medium

Your road bike size is:

Frame (cm)
Frame (size)

How do I measure myself? 

1. Measuring your height

Simply stand on a flat surface, upright against a wall with your legs together and shoulders back. Make sure you take your shoes off.

Place a pencil on top of your head and holding it parallel to the floor make a little mark on the wall.

2. Measure your inseam

Stand with your back against a wall (no shoes). Place a book or ruler between your legs at your crotch. 

Get a friend to measure from the floor to the top of the book/ruler, making sure it is level.

Bike sizing help & advice

How are bikes sized?

It is the different frame sizes that determines the size of adult bikes. The frame size measurements are typically based on the length of the seat tube; the near vertical tube that the seat post slides into. 

This measurement is taken from the centre of the front chain ring to the top of the seat tube. Manufacturers use slightly different methods for measuring their frames and there are also differences between types of bike.

Do sizes vary for different types of bikes? 

Road bikes and mountain bikes are sized slightly differently and the units used varies depending on use and brand. Road bike sizing is usually given in centimetres, while mountain bike sizes are quoted in inches. 

Many manufacturers will quote sizes as small, medium or large etc. on some or all of their models. 

Fortunately our size calculator takes away the guesswork as it suggests sizes in either inches or centimetres alongside manufacturers’ recommendations.

Can I use the size calculator for women's specific bikes? 

Yes, typically women’s specific bikes have different frames to unisex bikes but they are sized in the same way. Women tend to have shorter upper bodies than men so the frames are shaped differently. 

They tend to have shorter top tubes compared to a similarly sized unisex bike which means that female cyclist will feel less stretched out on women’s bike. 

As this doesn’t affect the seat tube length our size calculator is suitable for both unisex and women’s specific bikes.

What if I am between sizes? 

Sometimes our bike sizing calculator will recommend two different sizing options. This means that both the larger and smaller sizes recommended will be suitable. It is a personal choice but, if you are unsure, the rule of thumb is to go for the smaller size option. 

This is because it is easier to make a small bike bigger (by raising the saddle or fitting a longer stem) than it is to make a big bike smaller. 

How are kids bikes measured? 

Kids can start riding bikes as young as 2 years old. Kids bikes are measured by their wheel diameter and not their frame size. Sizes range from 12” balance bikes to 24” mini road bikes and mountain bikes.  

Getting the wrong sized bike can be frustrating and make cycling less enjoyable. The key thing is not to buy a bike they can ‘grow into’. Riding a bike that’s too big will be heavy, hard to manoeuvre and frustrating. This is not the way to start a love of cycling.  

Give them the best start by using our Kids Bike Size chart below

Kids Bike Sizing Chart


Wheel Size

Height (cm)

10” – 12” (balance bike) 

81 – 93  


89 – 102 


96 – 110 


102 - 117 


107 – 124 


113 – 131 


119 – 138 


124 – 144 



128 – 150 



132 – 156 



137 - 162 

** Please note all sizing information is to be used as a guide only and can vary for different models/type of product. For the most accurate sizing information, please call us on 01792 799508, email us at info@tredz.co.uk or chat with us on Live Help and we'll be happy to help.