Adult Bike Sizes

For adult bikes, there are no standard sizes and you will need to work out what size you need by using the advice of cycle shops, test riding and the guidelines below.

Adult bike sizes are judged by the frame size. This is usually a measure from the middle of the bottom bracket to either the very top of the frame where the seat post is inserted or the point where the seat tube and top tube meet.

As different manufacturers use different sets of measurements to determine their frame sizes, you cannot always be sure that a size that is right in one brand of bike will be right in another.

Bikes lined up on a bike rack

Size Guidelines

The main thing to check when buying a bicycle is that you can stand over the crossbar easily. Many of the other components e.g. saddle height and handlebar position can be altered easily (see Setting up your Bike), but if the frame itself is too big the bike will be difficult to handle and you may do yourself an injury if you have to stop in a hurry!

Stand astride the bike with your feet flat on the floor. Make sure there is enough clearance between yourself and the top tube of the bike. For mountain bikes and hybrid bikes, you need about 3" clearance, for road bikes and tourers, you can reduce this to about 1-2".

Once you have checked this, sit on the saddle and get someone to hold the bike upright for you. Reach forward and put your hands on the handlebars. Can you reach and turn the handlebars easily and reach the brakes properly? If it is slightly too far, you may be able to move the saddle forward so you can reach better, but if the bike is fundamentally too big, then this will not make enough difference.

Signs that a bike is too small include:

  • Having to raise the saddle to or beyond the maximum extension mark in order to get your legs straight on the pedals
  • Elbows sticking right out when your hands are on the handlebars
  • Head protruding a long way out over the handlebars/front wheel
  • On a very small bike, you may even have difficult turning the front wheel as your knees get in the way!

Women’s specific bikes

Some manufacturers offer their bikes in women-specific sizing. In the old days, this meant they had a shopping basket on the front, a lowered top tube and a floral design! These days, however, women’s bikes are of the same quality and durability as their men’s equivalents, but the frames are a slightly different shape to account for the fact that women tend to have shorter arms and longer legs than a man of the same height. The top tube is therefore slightly shorter, bringing the handlebars closer so women do not have to over-extend to reach the handlebars and brakes. They may also come with a slightly wider and differently shaped saddles, designed for a woman’s wider hips.