When it comes to buying a second-hand bicycle, one of the first questions that arises is how to choose the right size. Is an M or L size better for you? Or maybe a size 53 or 55? Don't worry, you're not the only one wondering! In 2025, with brand innovations and their different ways of indicating sizes, it can seem more complicated than ever. But here we help you understand it in a simple way.
Mountain bike or road bike? Understand the difference in sizes
First, it's important to know that the way a bicycle is measured varies depending on the type. For mountain bikes, sizes are usually indicated in inches. For example, an MTB with a 17.5-inch size means that the seat tube, which connects the bottom bracket to the saddle, measures exactly that: 17.5 inches. Now, some manufacturers are also starting to use centimeters, which adds some confusion.
On the other hand, road bikes are traditionally measured in centimeters. So, when we talk about a size 54 in a road bike, we are referring to the seat tube measuring 54 centimeters.
The change in frame geometries
Things haven't always been this complicated. Until the 1990s, bicycle sizes were quite universal. A size 54 from a brand like Orbea
was practically the same as a size 54 from Colnago. But this changed when Giant introduced frames with sloping. This term refers to the downward angle of the top tube, which altered the dimensions of the bicycle and how they were measured. Now, the fact that two bikes have the same seat tube does not mean they are the same size.
Nowadays, each manufacturer uses their own angles and frame geometries, which means that a person who is 1.70 m tall may need a size 17 in one brand and a size 19 in another.
Letter or number sizing system?
To add more complexity, some manufacturers prefer to use a sizing system based on letters: XS, S, M, L, XL... while others stick to the numeric system: 50, 52, 54, etc. A real mess, we know! But at Tuvalum
we have compiled information from more than 30 manufacturers to help you better understand how each system works.
Here is a conversion table that can guide you:
| Generic size | Size in centimeters | Size in inches |
|---|---|---|
| XS | 46, 47, 48, 49 | 14" |
| S | 50, 51, 52, 53 | 15", 16" |
| M | 54, 55, 56 | 17", 18" |
| L | 57, 58, 59 | 19", 20" |
| XL | 60, 61 | 21", 22" |
| XXL | +62 | +23" |
How to calculate your size according to your height
Okay, you already know that sizes can vary between brands and types of bicycles. But, how can you know which is your size? Most manufacturers offer guides based on height, although you should keep in mind that height is not everything. Two people who are the same height can have different leg lengths, which will affect the size they need.
For this reason, we have prepared a reference table that will help you find the right size according to your height:
|
You measure |
Road Size (CM) |
MTB Size (Inches) |
Generic Size |
|---|---|---|---|
| From 1.55 to 1.60 | 47 - 48 - 49 | 14 - 15 | XS |
| From 1.61 to 1.65 | 49 - 50 -51 | 15 - 16 | S |
| From 1.66 to 1.70 | 51 - 52 - 53 | 16 - 17 | S |
| From 1.71 to 1.75 | 53 - 54 - 55 | 17 - 18 | M |
| From 1.76 to 1.80 | 55 - 56 - 57 | 18 - 19 | M |
| From 1.81 to 1.85 | 57 - 58 - 59 | 19 - 20 | L |
| From 1.86 to 1.90 | 59 - 60 - 61 | 20 - 21 | L |
| +1.90 | +61 | +22 | XL |
The trick of measuring the length of your legs
To get an even more precise size, the key is to measure the internal length of your legs. Take off your shoes, stand with your legs straight, and measure the distance from the floor to your Inseam. You can use a book to mark the height. Once you have this measurement, you can calculate your ideal size.
- If it is a mountain bike, multiply your leg measurement by 0.21. For example, if your length is 90 cm, the size would be approximately 19 inches.
- For a road bike, multiply the length by 0.65. So, with 90 cm, you get a size of 58 cm.
This method is much more reliable than just relying on height, although it is not infallible. The geometry of frames is constantly changing, so factors such as arm length or your flexibility also come into play.
What happens if your size is between two measurements?
If, after calculating your size, you find yourself between two measurements, here are a couple of criteria to guide you:
- Biomechanical criterion: Measure your wingspan (the length of your arms from fingertip to fingertip). If it is greater than your height, choose the larger size. If it is smaller, go for the smaller size.
- Usage criterion: If you want a bike for racing or demanding routes, choose the smaller size. For more recreational or comfortable use, it is better to go for the larger size.
Get your bike size right
Choosing the correct bike size may seem complicated at first, but with the right information and a few simple measurements, you can make it much easier. At Tuvalum, we have worked to gather all the necessary data and offer you a complete guide so you can find your ideal second-hand bike without worrying about the size.
And if you still have doubts, you can always get a fitting or biomechanical study to make sure you choose the perfect bike for you.
Tuvalum Team
