With just a few quick taps on your smartphone, you can begin shopping for a new bike or electric bike in seconds. But wait, bikes are often sold in different sizes. So, what bike frame size is the right one for you?

Knowing which frame size is right for you can quickly help narrow your choices. This is why we include a 'bike frame size' filter in our bike categories to guide you to what bikes are available in your size.

After plenty of customer queries, however, we felt bike frame sizes warranted further explanation. In this guide, we detail how bikes are sized, why there are three different units to describe bike size and finally some general pointers that could help you find the right size bike.

Explaining bike frame sizes

Almost all bikes use one measurement to determine their frame size. It's the distance between the bottom bracket and the top of the seat tube.

The pink line shows the distance between the bottom bracket and the top of the seat tube. Image: Velorution

Usually, manufacturers will publish a table showing each frame size with an accompanying range of rider heights and sometimes an inseam measurement. The theory here is that the seat tube measurement has a direct correlation to the leg length of the rider.

Want to find out the recommended height for each bike size on our website? Click the 'Size Guide' button or find the accompanying information in the product description.

The three different units manufacturers use to describe bike size

Ready to be confused further? Yes? Good! Not every bike brand expresses the size of their bike's in the same manner, even if it still refers to the standard seat tube measurement. Some brands, including the likes of Gazelle and Schindelhauer, use CM (56cm) to explain their frame sizes.

Riding the correct size bike is key. Image: Velorution

Orbea and Kalkhoff opt for standard sizing units, like small (S), medium (M) and large (L). Whilst British brand Pashley still uses the traditional format of inches (20") to size their frames.

Frame Size DescriptorExplanation
Standard Sizing e.g. Small or SThe simplest method. It will still be related to the seat tube measurement.
CM e.g. 56cmThe most common method. Many bike brands use it to explain size.
Inches e.g. 20"An older method. Inches are still commonplace for sizing mountain bikes.
A table explaining the different bike frame measurement units.

When selecting your chosen bike size on the Velorution website, you'll always see the unit which the manufacturer uses.

Explaining our bike frame size filter

Seems simple enough, right? But sometimes even the same manufacturer will use slightly different CM sizes for different models: 46cm or 47cm for example.

Because of this disparity between model sizes and the different units used, we've grouped the different measurements into one 'Bike Frame Size' - a filter you can find on our bikes and electric bikes pages. Once you know your rough frame size, this should help narrow down your choices.

Bike FrameFrame Sizes
One SizeOne Size
XSXS, 45cm, 46cm, 47cm
SS, 48cm, 49cm, 50cm, 51cm, 17.5", 18"
MM, 52cm, 53cm, 54cm, 55cm, 56cm, 20"
LL,57cm, 58cm, 59cm, 22", 22.5"
XLXL, 60cm, 61cm, 62cm, 24.5"
XXLXXL, 64cm, 65cm
The size groupings we use to determine a general bike frame size on velorution.com

What size bike frame do I need?

Getting the right size bike is crucial, but for a city or commuter bike like we stock at Velorution, it's critical. Comfort is key when it comes to riding a bike day in, and day out and that starts with the right frame size. A good place to start is by measuring your exact height and your inside leg - that should at the very least give you some frame sizes to rule out.

The rider should be able to comfortably reach the floor when standing over the top tube of the frame. You'll often see this measurement referred to as standover height. Image: Velorution

Want to be more scientific? When riding a bike you don't just pedal with your legs, you also steer with the handlebars. Holding the handlebars shouldn't be a stretch nor should they be too high or too low. As such the length of the frame's top tube might determine whether a bike fits you nicely or not.

What are stack and reach?

Ultimately the description above is a long-winded way of explaining two more bike geometry buzzwords: stack and reach.

Stack is the measurement vertically up from the bottom bracket. Reach is the horizontal measurement from the headtube to the point it intersects with the stack line.

Explaining stack and reach visually. Image: Velorution

Generally speaking, a greater stack measurement moves the rider toward the vertical. If the stack remains the same and reach is increased, the rider will stretch out and their hands will be further away.

Stack and reach are helpful when it comes to determining sizing differences between manufacturers. It's like when a pair of jeans from one brand fits you perfectly and then a pair in exactly the same size from another is uncomfortable.

Here's an example: An Orbea Vibe, frame size medium, has a stack of 580mm and a reach of 395mm. A Schindelhauer Arthur, again size medium, has a stack of 590mm and a reach of 449mm. If you're short in the arms that 54mm difference in reach might be the difference between a comfortable ride and a bad back!

The most effective way of determining whether a bike is the right size is to book a test ride - that should really be the acid test of whether a bike will fit you, or not.

What to do if I'm in between bike sizes?

Being between bike sizes is a common occurrence. Should you go for the smaller or the larger frame? There are two simple methods you can do in front of the computer to help decide.

First, stand up with your legs straight - can you touch your toes? If you can, your flexibility will mean the smaller of the two frame sizes would suit you.

Your ape index is the second way to decide - it's effectively the ratio between your arm span and your height. If your arm span is longer than your height then your long arms may suit the larger frame. The larger frame will have a longer reach than the smaller frame.

It doesn't end there either. Exact sizing can be accounted for by making small adjustments to the saddle height, moving the saddle or choosing a different-sized stem - these are simple changes any Velorution store can help you with.

A one-size bike - will it fit me?

In yet another attempt to confuse you further, this section looks at bikes sold in one frame size. Brompton, Gocycle, Carbo and Tern are examples of manufacturers who produce only one frame size per model.

With design developments like the telescopic seatpost and telescopic handlebar, it's now possible to produce a one-sized bike that fits a variety of different riders. Brompton for example quote a recommended rider height for all of their bikes between 140cm to 203cm (4’7" to 6’8").

This standardisation is of benefit to the manufacturer vis-à-vis economies of scale, but it also suits the end user too. The Tern GSD or Moustache Lundi 20, for example, can (and should!) be used by different family members, friends or even work colleagues.

Unfortunately, if you sit at the bottom or top end of the height spectrum you might be out of luck when it comes to a one-sized bike.

That's the end of our bike sizing guide. On first inspection, it's a simple topic but look closer and you'll find choosing the right sized bike shouldn't be a split-second decision. Fire us a bike-size question in the comments below, contact us or speak to a Velorution store.