How to choose the right bike size: Calculate frame height for bike types

Step length is one of the most important factors when determining the right bike size. While body height only provides a rough guide, the stride length allows you to determine the frame height much more precisely. The background: people of the same height can have very different leg and upper body proportions. Conversely, a correctly determined leg length ensures an ergonomic sitting position, efficient power transmission and reduces the risk of strains.

You will need:

• Book or spirit level (with a straight edge)
• Measuring tape or folding rule
• Optional: a second person for support

How to measure your leg length correctly:

1. Preparation:
   Take off your shoes and stand against a wall with your back straight. Position your feet about 10-15 cm apart.
2. Position the book:
   Clamp a book or spirit level between your legs and bring it up to your crotch - similar to sitting on a bike saddle.
3. Check alignment:
   Make sure the book is parallel to the floor against the wall.
4. Mark the measuring point:
   Mark the top edge of the book on the wall or hold the measuring tape exactly at this point.
5. Measure the leg length:
   Now measure the distance from the floor to the mark. This value corresponds to your stride length in centimetres.

The value determined is the basis for calculating the optimum bike size in the next step using the appropriate formulas.

There are often different units, especially in the context of bicycles, so it is sometimes difficult to keep track. For example, frame heights are sometimes measured in cm, sometimes in inches or using letters (XS to XL). The following conversion factor will help you determine important sizes:

1 cm = 0.393701 inch

Based on the correct leg length, you can then calculate the appropriate frame height. The formula required for this is

Stride length x factor for MTB/road bike/etc. (cm/inch) = frame size (cm/inch)

We have summarised the respective factor for each bike category in cm and inches in the table below.

In contrast to adult bikes, the frame height for children is not dictated by the length of the seat tube, but by the wheel size - these are usually given in inches.

Determine bicycle size for children

Despite the correct leg length and the corresponding formula, you may still find yourself between different sizes. Depending on your decision, your riding position and the riding experience will change.

A larger frame means ...

• A more stretched upper body position: You sit slightly longer towards the handlebars because the top tube and wheelbase are longer.
• More space "in" the bike: You have more freedom of movement between the saddle, handlebars and bottom bracket, which can be an important point when mountain biking.
• Knee and hip angles slightly more "open": With the correct saddle height, the joint angles tend to be slightly flatter, which is more comfortable at high pedalling frequencies.
• More pressure on the hands: Due to the shifted position, more body weight moves onto the hands, which can put more strain on the forearms and shoulders.
• Smoother ride: A longer wheelbase and often flatter geometry make the bike more stable at higher speeds.
• Less agile: Turning is somewhat slower, tight bends and quick changes of direction feel less playful.
• Front stays on the ground: The increased pressure on the front wheel means it doesn't climb as easily on steep climbs.

A shorter frame means ...

• Upright riding position: A shorter top tube and wheelbase mean that you sit more compactly, which can make you feel more relaxed.
• Less space "in" the bike: The space between the saddle and handlebars shrinks, reducing freedom of movement.
• Less pressure on the hands: The weight moves slightly back towards the saddle, relieving pressure on the hands.
• More agility: A shorter wheelbase makes the bike more manoeuvrable, making it easier to change direction.
• Less smoothness: The bike feels more nervous at high speeds.
• Rising front tyre: Due to the shorter wheelbase and more compact centre of gravity, the front wheel lifts off more easily on steep climbs.

If you are between two sizes, our RENTertainers will help you choose. They not only take into account the bike category, but also your individual wishes and riding behaviour.

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You're not sure how big your bike is and it's not written on the frame or on the invoice? Our experts will show you how to measure correctly - you will also need a tape measure or folding rule:

• Measure from the centre of the bottom bracket (crank axle) to the top of the seat tube: this is the common "centre-to-top" frame height.

Our bike experts have a lot of experience when it comes to finding the right model. If you have any questions about size, the staff in one of our more than 800 shops worldwide will be happy to help you at any time. They will also have a tip or two for a tour in the neighbourhood.

The 26-inch wheel size is considered the outdated standard for mountain bikes. Nevertheless, 26-inch models can be found on children's and youth bikes - even smaller adults can benefit from them. In this case, a height of 135-165 cm is generally assumed.

A bike with a wheel size of 16 inches is a children's bike. In principle, this type of bike is suitable for children aged 5 to 6 years. However, due to the different development in relation to height, this is the more important factor. From a height of 105 cm to 120 cm, a 16-inch children's bike is the right choice.

The saddle offset refers to the displacement of the saddle on the horizontal plane. Among other things, it determines how stretched or compact you sit on the bike. The offset is also a factor in power transmission, as it influences the leg angle. The amount by which the saddle is shifted forwards or backwards is in relation to the pedal axis and is usually determined using a plumb line.