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Bicycle Frame Sizing Guide: What Size Bike Do I Need?

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A very basic thing required when shopping for bikes is the understanding of size and measurements. Getting the proper size of the bike is very important, if the fit is good the bike will be more comfortable and easier to handle.

How to measure a bike?

Bikes are generally measured and defined by the length of the seat tube – the part of the bike that the seat post (and saddle) slide into. This measurement is normally from the centre of the bottom bracket (BB) or the centre of the bolt that attached the crank arms. This differs by brand, some measure to the top of where the top tube meets the seat tube, or even the centre of the top tube.

bike-frame-size

How to fit a bike?

There are 2 mainly measurements — your height and your inside leg(inseam) — that will assist you in choosing the right size bike. Hold a coffee-table book or carpenter’s square between you legs with one edge against the wall to keep the edge in your crotch exactly level. Raise the book until it stops snug against your crotch. Measure from the floor to the top edge making sure the book’s other edge is still flat against the wall.

Bike size calculator:

  • Applies to bike size centimeter — For road bikes — your inside leg(cm) X 0.665 = bike frame size [cm].
  • Applies to bike size inch — For mountain bikes — your inside leg(cm) X 0.226 = bike frame size [in].

One inch equals 2.54 cm. If the theoretical value is in-between two sizes, alternatively you may reference to your height with the help of the chart below.

If your height and inside legs measurements put you in between sizes, your upper body should be the deciding factor. If your arm span is greater than your height then we suggest you go for the larger of the sizes. Otherwise, choose the smaller one.

Women’s bike size

On average, women have longer legs and shorter torsos than men of the same height, so female specific bikes have a shorter top tube, narrower handlebars and female specific saddles.

As a general rule, if you are shorter than about 5ft 5 (165 cm) or have felt too stretched on mens/unisex bikes previously, you may be more suited to a female specific bike which offers smaller frame sizes.

However, people are not “averages” and a bike should be the perfect fit for you individually, whether it is a unisex bike or a women’s specific fit.

Bike size chart

Traditionally measurement is given in metric (cm) for road bikes, and imperial (inches) for mountain bikes. Folding bike size is a all in one type. Except the BMX bike size, for other types of bikes size can refer to the road or mountain bike chart as well as applies formula above.

Interestingly, once you do figure out what frame size you are on a certain bike it does not mean that you are that frame size on another bike! This might cause confusion, though two bike companies may list the same model bikes, there may be a huge difference in the measurements of the bikes.

Make sure you’ll be able to stand over the bike frame with a minimum 2cm gap between you and the top tube, the idea of being able to stand over the frame did not occur immediately and to prevent accidental bruise if you slip off the pedals.

Road bike sizing:

  • bike size 49~51cm, rider fit: 5’0″ – 5’3″ (152 – 160cm).
  • bike size 52~53cm, rider fit: 5’3″ – 5’6″ (160 – 168cm).
  • bike size 54~55cm, rider fit: 5’6″ – 5’9″ (168 – 175cm).
  • bike size 56~57cm, rider fit: 5’9″ – 6’0″ (175 – 183cm).
  • bike size 58~60cm, rider fit: 6’0″ – 6’3″ (183 – 191cm).
  • bike size 61~63cm, rider fit: 6’3″ – 6’6″ (191 – 198cm).

Mountain bike sizing:

  • bike size 13″ – 14″, rider fit: 5’0″ – 5’2″ (152 – 158cm).
  • bike size 15″ – 16″, rider fit: 5’3″ – 5’6″ (158 – 168cm).
  • bike size 17″ – 18″, rider fit: 5’6″ – 5’10” (168 – 178cm).
  • bike size 19″ – 20″, rider fit: 5’10” – 6’1″ (178 – 185cm).
  • bike size 21″ – 22″, rider fit: 6’1″ – 6’5″ (185 – 193cm).
  • bike size 23″ – 24″, rider fit: 6’4″ – 6’6″ (193 – 198cm).

Many bikes today are made with a sloping top tube, is known in cycling parlance as a compact frame. With a horizontal top tube, as the frame’s head tube gets longer, the seat tube must follow suit, which often results in a battle between the ideal handlebar height and ideal standover height.

The sloping top tube is not constrained to being level with the ground, the frame’s designer is free to use any head tube length and it is easier for cyclists to get a good fit. But also, it cuts down the amount of different frame sizes that the manufacturer has to produce as now they need only small, medium and large and then possibly an extra small and an extra large. That also greatly reduces the inventory burden of the manufacturer.

Sizing a bicycle is not an exact science, this a rough guide. And, kids bikes are measured and sized in a different way from adults bikes. These are usually category in age ranges and wheel sizes.