Road bike sizing: what size bike do I need?

Use our guide to ensure you choose the correct frame size

Riding a bike that doesn’t fit is no fun. It’s uncomfortable and you risk injury from being too cramped or too stretched out, but knowing what size bike you should get can be a bit of a minefield. So here's some advice to help you decide on which frame to go for — traditional, semi-compact or compact — and to help you find your perfect size.

Getting the right fit means more than just having the right size frame. It also means your bike fits at all the main contact points: saddle, handlebars and pedals. Have a read of our road bike positioning article to achieve the perfect setup.

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Of course, we’re not all the same, so use the information below as both a starting point and a guide. After you get the position close using these tips make smaller adjustments based on what feels better. 

You'll be able to get fit advice in person from a bike shop, though we'd recommend getting an understanding of the different elements that affect how a bike fits to ensure you end up with the right size. We also recommend taking any bikes you are considering for a test ride to gauge how they feel in action. 

Manufacturers' size guidelines

The simplest way to determine what size bicycle to go for is by using the guidelines bicycle manufacturers provide, which correlate various height ranges with different bike sizes. 

However, there are no standard sizes between the bicycle manufacturers, and each will have their own approach to bike design, so it's useful to have an understanding of bike geometry and how that affects the fit to ensure you get the size that suits you best. 

Anatomy of the bicycle frame

Bike manufacturers will usually list the measurements for each element of a bike's geometry, so knowing what each measurement refers to is the first step.

Use this diagram below to help you identify the different tubes used on the frame of a road bike. The effective top tube, shown in the diagram below, concerns bikes that use a sloping top tube (road bikes with a semi-compact or compact geometry).

With experience you will soon find that a correctly sized bike will look in proportion when finally set up.

This diagram shows the various tubes that make up a road bike frame
This diagram shows the various tubes that make up a road bike frame

Manufacturers make frames in various sizes to suit the variety of riders. Getting the size right is essential, but this step is only halfway there. The fine-tuning starts when you choose the length of the stem and the width of the bars.

Frame geometries: traditional, semi-compact and compact

There are three geometries of frame size to consider when buying your first bike: traditional, semi compact and compact.

Traditional bicycle frame

Traditional frames are characterised by a top tube that runs parallel to the ground. There is a reduced space when standing over the bike, however, so sizing can be more critical here.

This Fondriest road bike has a traditional geometry frame with a top tube parallel to the floor
This Fondriest road bike has a traditional geometry frame with a top tube parallel to the floor

Compact bicycle frames

Compact frames are meant to look more radical than conventional level top tube frames so expect to see an extra two to three inches of seatpost showing when compared with horizontal-top tube bikes.

The contact points should be exactly the same, so be aware of this when buying — a compact should feel exactly like your preferred conventional road bike with respect to riding position.

Compact geometry frames are characterised by a sloping top tube, shorter wheelbase and smaller rear triangle of the frame. The result is more standover clearance than a traditional geometry frame and a possibly stiffer but more responsive ride.

This Ribble road bike features a compact frame with a sloping top tube
This Ribble road bike features a compact frame with a sloping top tube

Semi-compact bicycle frames

Semi-compact geometry is similar to a compact with the only difference being that the sloping angle of the top tube is not as great, so the standover clearance is reduced and the effective top tube distance is slightly longer.

A very narrow sloping top tube indicates that this Cannondale road bike has semi-compact geometry
A very narrow sloping top tube indicates that this Cannondale road bike has semi-compact geometry

Important lengths

The most important consideration to make as you decide which frame to go for is the effective top tube length: the distance from the head tube to the seatpost on a bike with a sloping top tube, or simply the length of the top tube on a road bike with traditional geometry. 

Get the top tube length too long and you'll be overreaching to the handlebars, using a flatter riding position akin to a racing position, which could be uncomfortable on longer rides.

If you're looking for a more comfortable riding position then you may wish to go for a shorter effective top tube length. Use the chart below for a rough guide on the frame size to go for.

This table should act as a starting point for finding your most suitable frame size
This table should act as a starting point for finding your most suitable frame size

Tweaking the bike fit

Once you've decided on your frame size you can fine tune your bike fit. 

The next critical adjustment to make is setting the bar and saddle height. Check out how to get your bike seat right to get you started.

You may also want to adjust or change the stem, as that can also affect your reach — literally, how far you are reaching forward to the handlebars — and also the handling and performance of the bike. 

Further tweaks can include adjusting the fore/aft position and tilt of your saddle, the angle of your handlebars, and the distance to the brake levers.

Many of these changes can be made in a good bike shop, though a bike fit is also worth its weight in gold. As part of a bike fitting session, bike fit experts will get you riding on a fixed trainer to check your bike position and ensure everything fits you perfectly. 

Women who have opted for a unisex bike may find our guide to the most common adjustments that make these bikes more female-friendly useful. 

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