Bike Size Calculator

The bike size calculator tool will calculate the suitable frame size based on body measurements such as height and inseam. It is the fastest way to answer the question "What bike size do I need?" and especially important when buying online where test riding isn't possible. After selecting your bike type and entering your measurements, you can also see the recommended frame size, saddle height and reach at the same time.

How to determine bike size?

The frame size is usually the distance from the center of the bottom bracket to the top of the seat tube (where the seat post clamps on). This is an important number for determining if a bike will fit, but the measurement method varies by type of bike.

Road and gravel bikes are measured in centimeters. Mountain bikes are either measured in inches or size categories such as Small/Medium/Large. For the same height, mountain bike is usually smaller to ensure enough overhang and shorter reach. Hybrid and city bikes fall somewhere in between. Children's bikes aren't sold by frame size but wheel size.

The formula for calculating size:

This tool calculates the adult frame size based on stride length. The length of the inside leg is a more accurate indicator of overhang than just height alone. As there are people with similar heights but very different leg lengths, an estimate based on stride length is a more reliable starting point. The following factors come from French trainer Cyrille Guimard who coached several Tour de France winners and were later popularized by Greg LeMond.

For mountain bikes, about 11 cm is subtracted from the road bike values. So a mountain bike frame will usually be around 4 to 5 inches smaller than a road bike frame when leg length is equal. If only height is known, the calculator estimates stride length as being roughly 47 percent of your height but a measurement is always more accurate.

Example calculation:

Let's say a rider has an inseam length of 81cm and wants a city bike. The commuter bike factor is 0.64, so the recommended frame size would be calculated by multiplying 81 by 0.64 and rounding up to approximately 52cm. If the same rider were riding a road bike, the frame size would be around 54cm (calculated by multiplying 81 by 0.67), while for a mountain bike it would be about 43cm smaller.

Even for the same rider different bike types will result in different frame sizes. This shows that both the type of bike and the measurements are equally important and it is wrong to compare road bike values directly with mountain bike ones.

Adjustment of saddle height and standover distance:

When the frame is the right size, saddle height affects comfort and pedaling efficiency. A common starting point, as suggested by Greg LeMond, is 0.883 times your leg length, measured from the center of the bottom bracket to the top of the saddle.

Begin here with adjustments so that your knees are slightly bent when the pedal is at its lowest point. Avoid fully straightening your legs. Also, avoid moving your body sideways to reach the pedals. Standover height is another important measurement. This refers to the distance between the top tube of the frame and your inseam while you're sitting on the bike. Road bikes should have a standover height of at least one inch (2.5 cm), while mountain bikes should be higher. This will allow for safe dismounting.

Children's bikes are sized by wheel diameter.

Children's bikes are sized by wheel diameter rather than frame size. A 16 inch bike has wheels with a diameter of 16 inches, a 20 inch bike has wheels with a diameter of 20 inches, and so on. Choose a wheel diameter that fits your child's stride length and make sure both feet can touch the ground firmly when they are sitting on the bike. When choosing size, it is important to consider how comfortable your child will be rather than opting for a larger size that may fit better in years to come.

Frame sizes based on height (Quick reference)

If you want to find a suitable size directly from the table, use this table to match your rider height with recommended frame sizes for road bikes, gravel bikes and mountain bikes. The values given are rounded starting points. If your height falls between two rows, then a smaller size will offer a more athletic position while a larger size offers more comfort.

This is how you measure your stride.

Take off your shoes and stand with your back against a wall with your feet about 15 to 20 cm apart. Place a hardcover book vertically between your legs and press it firmly against your crotch like a saddle. Mark the top edge of the book where it touches the wall, then measure straight down to the floor. This distance is your hip measurement for this tool.

As each bike brand and model has its own geometry, these values should be considered as a good starting point. They are not guaranteed values. The most reliable method of fitting is still to test ride a bike. If you do a lot of riding or experience pain, it's worth considering a professional bike fit.