What Size Bike Do I Need and How Are Bike Frames Measured?

If you are just starting out with cycling or looking to upgrade your existing bike, choosing one can seem like a daunting task. There are so many different varieties and sizes on offer. 

If you intend to take up cycling regularly as a hobby or for your commute to work, you’ll want to ensure that your bike is as safe and comfortable as possible and getting the right size is a key factor in this. 

How Are Bikes Sized?

Adult bikes are measured by frame size. Most modern bike brands and manufacturers will measure the frame from the centre of the crank axle to the top of the seat tube. Road bikes are generally measured in centimetres, mountain bikes in inches and hybrid bikes will be either of the two. Children’s bikes are usually measured by wheel size rather than frame size.

Sometimes measurements will vary between brands and manufacturers so the best thing you can do is to take your own measurements before you go shopping. This will make it much easier to select the size range to look at when considering the purchase of your chosen bike.

Which of Your Measurements Do You Need?

The main measurement you will need to help you to select the right size bike frame is your height. You may need to enlist help from a friend to help you to take an accurate measurement. 

The easiest way to measure your height is to stand up straight against a wall and to make a mark on the wall which is level with the top of your head. You can then use a measuring tape to measure the distance between the ground and the pencil mark.

If you are planning to purchase a road bike, the other important measurement that you will need is your inseam measurement (otherwise known as your inside leg measurement.) To measure your inseam, you need to stand barefoot with your legs shoulder-width apart and measure from the ground up to your groin. Again, you can make a pencil mark on the wall to measure to if it’s easier. 

Your inseam measurement will help you to establish the correct stand-over height needed. The stand-over height is the distance between the ground and the top tube of the bike. Ideally, for maximum comfort, you will want to ensure that there is at least one inch between your inseam and the top tube. The clearance between you and the frame will also help you to prevent injuries should you need to quickly dismount from your bike.

Mountain Bikes

You most likely will not need your inseam measurements in order to select the right size mountain bike. This is because mountain bike frames tend to have smaller frames to make them more manoeuvrable over rough terrain. The stand-over height on a mountain bike, therefore, tends to be lower than it is on road bikes. 

The below chart gives a good indication of what the best frame size for you is likely to be based on your height.

Road Bikes

Selecting the correct size frame is important, particularly when purchasing a road bike. Most of your time using a road bike is spent sitting in the saddle and having the correct size is a key factor in your safety and comfort during use and will greatly reduce your risk of injury. It’s also worth noting for those of you who are riding competitively (even if you are only competing against yourself by trying to smash your PB) that using the right size for you should also positively impact your performance. 

The below chart gives a good idea of what frame size is likely to be right for you based on your height and inseam measurements. 

Children’s Bikes

Children’s bikes are measured based on wheel size. It’s a good idea to search by age range and to further narrow down by the height of your child. A 2-inch gap above the top tube should ensure that the bike is a comfortable fit for your child, although most kids bikes with a wheel size of up to 20 inches should have a low stand-over height regardless. 

The below size chart shows a good indication of what will most likely be the best size for your child based on their age and height.

Conclusion

Selecting the right frame size for your bike is of utmost importance to ensure maximum comfort and performance. Whilst this guide should give you a good idea of how bikes are measured and how to select the right frame size, it is worth remembering that sizes may differ slightly between brands and manufacturers. Most modern bike brands, manufacturers and shops will try to make it easy for you by having a size guide listed on each bicycle, so as long you are armed with your measurements it should be relatively simple. 

Your body type and personal riding style will also have an impact on what the right frame size is for you. For example, some people may have long legs and a short torso or vice versa so you may find that a frame size that suits somebody else of your height may not be an exact match for you. Because of this, ideally, you’d also want to take your chosen bike out for a test ride to try before you buy, particularly if buying second hand and there are no size guides available. Buying any bike is an investment and you need to make sure it’s the right fit for you! 

Before hitting the shops, you may want to check how much you should be spending on your new road bike and what other equipment you may need before you jump in the saddle.

Further Reading:

• Knee Pain When Cycling
• The Best Stretches Before Cycling
• How Much Should I Spend When Buying a Road Bike?
• What do I need to get started cycling?
• Is Cycling Better Than Running