The right frame size is a prerequisite for a long and healthy enjoyment of a bike. It is the basis of a suitable seating position that protects your back and leg muscles. Only with the correct seating position are you able to get the most from your bike and benefit from optimal riding performance.
The seating position also depends on the type and purpose of your bike. For instance, the right position on a road bike is different from that on a mountain bike. Anatomic factors and the preferences of the rider also affect the seating position. The position can be precisely configured by adjusting the handlebars, stem, seat, and seat post. Moreover, the bike’s geometry is highly complex: The frame size has an effect on many other aspects and dimensions that are important for optimal riding performance and fatigue-free tours.
As a consequence, it is key to calculate the best frame size for your bike. The frame size should correspond to the distance between the middle of the crank axle and the upper end of the seat tube. The distance is indicated in either centimetres or inches; one inch is equal to 2.54 centimetres. At BIKE24, you’ll find the frame size for each bike model in a table that belongs to the respective article figures – under the item “Seat tube length”.
There is no general answer for which frame size is suitable for what body size. Looking up the bike size from a table based on body size only gives an approximation. Apart from that, adults and children need different information in order to find out which bike size may best suit them.
Adults can determine the bike size by measuring their inseam length and then multiplying it by a certain factor – depending on the type of the bike. The right bike size for children depends on their body size.
The calculation is based on the inseam length (or step length), from the ground up to the crotch. The measurement is taken without shoes and in tight-fitting pants (such as cycling shorts) or underwear. To measure your inseam length, you need to slide a book or water level between your legs up to the crotch. A second person now measures the distance between the ground to the upper edge of the book or water level. This is the inseam length, which you’ll need for the next part of the calculation.
To figure out the right frame size, the inseam length is now calculated by a certain factor. This factor depends on the type of the bike:
Now you know the right frame size (seat tube length) for your new bike. However, some manufacturers also use different dimensions for specifying the frame size of their bikes. The right frame size for your bike is also affected by other factors:
As you can see, it’s not that easy for a layperson to calculate the correct frame size for a bike. Our bike experts are therefore happy to help you find out which frame size is best for your new bike – naturally considering your body size, preferred seating position, intended use, and other aspects.
Just like the frame size, the seat height is also dependent on various factors. However, you can calculate an approximate seat height by multiplying the inseam length in centimetres by a factor of 0.885. Example: 84cm (inseam length) x 0.885 = 74cm (seat height).
In the case of kids’ bikes, the size is not determined by the frame but by the wheels. Unlike for adults, no exact calculation is performed here. Instead, the size of the wheels is determined by the body height of the child. Over time, approximate reference values have emerged that can help in this respect.
If you really liked your old bike and would like to use the same frame size for your new bike, it’s a good idea to measure your bike’s frame size.
How do you measure the frame size of a bike? Place the measuring tape exactly in the middle of the crank axle and measure the distance to the upper end of the seat tube. This dimension – in centimetres or inches (divided by 2.54) – corresponds to the frame size. However, some manufacturers have other specifications they use to classify frame sizes. So, make sure to check the measurements against our seat tube tables in the article figures. If in doubt, please feel free to contact our customer service team.