Biking is an incredible way to stay active, have fun, and explore the world around us. With the rise of online shopping, buying a bike or electric bike has never been easier – but it also means that test riding a bike before purchasing it has become a challenge. This is why measuring your bike frame size accurately is more important than ever. Not only does it make the process of buying a bike more straightforward, but it also ensures that you end up with a bike that fits you perfectly.
But that’s not all. If you’re looking to sell or buy a used bike, measuring the frame size is crucial to ensure that the bike fits the buyer comfortably and safely. Knowing the frame size will also give you a better idea of the bike’s value, making the buying and selling process smoother and more straightforward.
So, what measurements are important when determining your bike frame size? It all starts with your body measurements. Measuring your inseam length, torso length, and arm length can provide a good starting point in finding the right size bike frame. Usually, you can directly check a bike size chart to find your best fit size.
With our guide, you’ll learn everything you need to know about how to measure your bike frame size accurately, including seat tube length, top tube length, reach, and so on, and what factors to consider when making your decision. So, grab your measuring tape, let’s get started, and find the perfect bike for you!
The Easiest Way to know Your Bike Frame Size
The quickest and most straightforward way to find out your bike frame size is by checking the size sticker on the bike itself or the manufacturer’s specifications on their sites.
If you’re in the market for a new bike, you can find the size sticker on the frame itself, usually near the bottom bracket or seat tube. The frame size is typically listed in inches or centimeters and represents the length of the seat tube, which is part of the frame that holds the seat post and saddle.
If you’re shopping online, make sure to check the product description for the frame size information. The manufacturer should provide detailed specifications and measurements for each bike they sell, including the frame size.
Sometimes, however, it’s impossible to check such information on a bike. Never mind. Now follow us to measure bike frame size by hand.
How to Measure Seat Tube Length (ST)?
The seat tube is part of the bike frame where the seat post attaches and runs down to the bottom bracket. It’s usually measured in centimeters.
Regardless of whether it’s a road or mountain bike, the size of the seat tube is crucial. Choosing the wrong one can damage the frame and lead to back discomfort.
To measure the seat tube length, you’ll need a measuring tape or a ruler. Here’s the step-by-step tutorial to measure the seat tube length:
- Identify the center of the bottom bracket, which is located at the bottom of the frame and houses the crankset and bottom bracket bearings.
- Measure the distance from the center of the bottom bracket to the top of the seat tube, which is where the saddle would be inserted.
- Record this measurement in either inches or centimeters.
Note that some bike brands or manufacturers list the effective seat tube length, which is the length of the seat tube minus the amount of seat post that is inserted into the frame. Make sure to check the manufacturer’s specifications to ensure that you are measuring the correct length.
How to Measure Top Tube Length (TT)?
The top tube is the horizontal part of a bike’s frame that runs from the head tube (the front of the bike frame) to the seat tube in the back. The top tube length is the horizontal distance from the center of the head tube to the center of the seatpost, which determines the reach from the saddle to the handlebars. It has a big impact on the comfort and efficiency of your riding position.
But on modern bikes, the top tube is not always perfectly horizontal. For example, on road bikes, the top tubes are typically parallel to the ground, but on mountain and BMX bikes, they can slope from front to back at different angles.
It means, when you see the top tube measurement of a bike frame size, it isn’t necessarily indicating the length of the tube. It can actually be the imagined horizontal length. To account for this, the measurement is often referred to as the virtual top tube length or effective top tube length. This is a more useful way to talk about the reach of the bike, and also to compare bikes that have different frame geometry.
So, if you need to measure the traditional top tube length:
- Stand the bike upright.
- Measure the distance from the center of the seat post to the center of the head tube.
- Record the measurement.
But if you want to measure the virtual or effective top tube length, you’ll need a long straight ruler and a spirit level, and then follow this:
- Place the bike on a level surface, and make sure it is stable and will not fall over.
- Measure the traditional top tube length as above.
- Measure the height of the top tube slope. You should measure the vertical distance from the center of the head tube to the center of the seat post.
- Calculate the effective top tube length using this equation: Effective top tube length = √(Traditional top tube length^2 + Height of top tube slope^2).
Here’s an example of using this equation.
Let’s say that you measured the traditional top tube length to be 56 cm and the height of the top tube slope to be 8 cm. To calculate the effective top tube length, you would use the equation:
Effective top tube length = √(Traditional top tube length^2 + Height of top tube slope^2) = √(56^2 + 8^2) = √(3136 + 64) = √3200 = 56.57 cm
So in this example, the effective top tube length would be 56.57 cm. This measurement would give you a more accurate representation of the reach from the saddle to the handlebars, taking into consideration the slope of the top tube.
How to Measure Reach and Stack?
Reach and stack are the two most important frame measurements when choosing a new bike. They aren’t a measurement you can easily alter, but they are an important guide to the positioning of your saddle and handlebars on a frame.
Specifically, reach refers to the horizontal distance from the center of the bottom bracket to the center of the head tube. This measurement determines the length of the bike and the rider’s reach to the handlebars.
To measure reach, you will need a long straight ruler and a spirit level. Place the spirit level on the ruler, making sure it is level. Then, measure the horizontal distance from the center of the bottom bracket to the center of the head tube. Record this measurement as the reach.
Stack, on the other hand, refers to the vertical distance from the center of the bottom bracket to the top of the head tube. This measurement determines the height of the bike and the rider’s upright posture.
To measure the stack, you will need a ruler and a plumb bob. Hold the plumb bob vertically from the center of the bottom bracket and measure the distance from the center of the bottom bracket to the top of the head tube. Record this measurement as the stack.
While effective top tube length and height may be important, they are not as significant as reach and stack when it comes to fit. These measurements provide a more accurate picture of the bike’s fit and how it will feel while riding.
Additionally, reach and stack are a standard that many manufacturers have adopted and it makes comparisons between bikes a lot easier.
How to Measure Head Tube Length?
The head tube length affects the riding position, the handling of the bike, and the overall comfort of the ride. A longer head tube length can provide a more upright and relaxed riding position, which is ideal for recreational riders who want a comfortable and easy ride. On the other hand, a shorter head tube length can create a more aggressive and aerodynamic riding position, which is better suited for performance-oriented riders who want to achieve maximum speed and efficiency.
To measure the head tube length of your bike, you will need to stand it upright on a level surface. Using a measuring tape or ruler, measure from the bottom of the head tube to the top.
The head tube length can also be affected by the stem height, which can be adjusted to suit the rider’s individual needs. A shorter stem will provide a more upright riding position, while a longer stem will create a more aggressive, aerodynamic position.
Besides, the head tube length can vary greatly between different bike models and manufacturers. So, it’s necessary to check the manufacturer’s specifications for the exact measurements.
How to Measure Chainstay Length (C)?
The chainstay length is an important aspect of the bike frame as it affects the handling and stability of the bike. A shorter chainstay length offers more agility and makes it easier to do tricks like manuals and wheelies. However, it also reduces the overall wheelbase length, which can affect stability. On the other hand, a longer chainstay offers a smoother and more centered ride by keeping the rear wheel closer to the rider’s center of gravity. It also provides more clearance for panniers, making it ideal for commuting and touring bikes.
In general, road and city/commuter bikes benefit from shorter chainstays to enhance agility and traction. Meanwhile, trail and enduro bikes often feature longer chainstays to accommodate larger tires and improve stability.
To measure the chainstay length, you’ll need to start by locating the center of the bottom bracket, which is the pivot point for the cranks. From there, measure the distance from the center of the bottom bracket to the center of the rear axle. This measurement is the chainstay length.
It’s also worth noting that chainstay length can be affected by the choice of components, such as the size of the tire. For example, a long chainstay may be needed to accommodate larger tires on a mountain bike or a heavy front tire on a road bike. Additionally, short chainstays can make it challenging to fit a rear rack and panniers.
In terms of weight savings, shorter chainstays tend to be lighter, but the total tubeset engineering, including tube profile and butting, has a bigger impact on weight.
How to Measure Bottom Bracket Height?
The bottom bracket height refers to the distance between the ground and the center of the bottom bracket, which is the rotating axle that connects the pedals to the frame. It affects the handling of your bike. A bike with a lower bottom bracket height provides more stability and is often preferred for trail riding and off-road use. On the other hand, a bike with a higher bottom bracket height provides more agility, which is commonly used for road racing and time trial events.
To measure bottom bracket height, you’ll need a level surface and a measuring tape or a ruler. First, place your bike on a level surface, making sure it’s stable and not leaning in any direction. Then, measure the distance from the ground to the center of the bottom bracket.
How to Measure Bottom Bracket Drop (BB)?
The bottom bracket drop is the difference between the height of the bottom bracket and the height of the axles of the wheels. It affects the stability and handling of the bike, especially when riding on rough terrain.
Once you have the measurement of the bottom bracket height, you only need to measure the height of the axles of the wheels, which is the height from the ground to the center of each axle. Then, minus the height of the bottom bracket from the axle height.
How to Measure Wheelbase (WB)?
The wheelbase is the distance between the front and rear axles of a bike. The longer the wheelbase, the more stable the bike will be. On the other hand, the shorter the wheelbase, the faster response and more agile handling the bike will be. The longer wheelbase is ideal for rough terrain or long-distance riding, while the shorter is suitable for tight turns and technical riding.
To measure the wheelbase of a bike, you need to:
- Stand the bike up on a level surface and place a tape measure on the ground next to the front axle.
- Extend the tape measure to the center of the rear axle.
- Measure the distance between the front and rear axle and record the measurement.
- Repeat the process for both wheels to ensure that you have an accurate measurement.
How to Measure Front Center?
The front center of a bike frame refers to the distance from the center of the bottom bracket (where the pedals are attached) to the intersection of the head tube and the top tube. Like the wheelbase, the front center also affects the stability of the bike. The longer it is, the more stable it can provide. However, a longer front center can also lead to a more stretched-out riding position, which can be tiring for some riders, especially on long rides.
To measure the front center, you need to stand your bike upright on a level surface and make sure the front wheel is straight. Then, measure from the center of the bottom bracket to the center of the front axle.
How to Measure Head Angle (HA)?
Some manufacturers may also provide head angle information in their specifications, though not all do this. The head angle of a bike is the angle formed by the head tube and the ground. A steeper head angle means the bike will be more responsive and nimble, while a slacker head angle will provide more stability and control.
To measure the head angle of a bike, you’ll need a protractor or angle finder tool. First, place the bike on a level surface and ensure that it’s upright. Then, place the protractor on the top of the head tube, making sure it’s level. Finally, measure the angle between the ground and the protractor, which will give you the head angle of the bike.
BTW, some bikes may have adjustable head angles, which can be changed to suit the rider’s individual preferences and needs.
How to Measure Stem Length?
The stem of a bike is the component that connects the handlebars to the bike’s frame. It’s usually made of metal or composite material. It comes in various lengths, and the length of the stem will determine the rider’s position and handlebar height. A longer stem will make the bike feel too stretched out and affect the rider’s control over the front wheel. On the other hand, a shorter stem will make the bike feel too compact and affect the rider’s ability to steer and balance.
Some stems may have a marked measurement, but if not, you can measure it yourself. With a ruler or a tape measure, measure the distance from the center of the steerer tube to the center of the handlebar clamp.
Once you have measured the stem length, you can determine if it is the right length for you.
How to Measure Bike Size for Kids?
Kids’ bikes are typically sized by wheel size, rather than frame size as in adult bikes. The wheel size is an important factor in determining the appropriate bike size for a child, as it impacts the overall height and fit of the bike. Here’s how to determine the wheel size of a kids’ bike.
To measure the wheel size, you will need to measure the diameter of the wheel, from one end of the tire to the other, through the center of the wheel. The wheel size is typically measured in inches or millimeters.
It is important to note that there are different wheel sizes available for kids’ bikes, including 12″, 14″, 16″, 20″, and 24″. A 26-inch bike is generally considered an adult size and is not typically recommended for kids. However, some older children and teenagers with a height of 5’6″ or more may fit on a 26-inch bike, too.
To determine the right wheel size for your child, consider their height and skill level as well. As a general rule, a child should be able to touch the ground with both feet while seated on the saddle. This will ensure that they have proper control and balance while riding.
You can consult a bike sizing chart for kids to get a more specific recommendation based on your child’s height and inseam.
OK. That’s all the important measures you may need to measure your bike frame. To make it easier to check, we’ve put them together as a glossary below.
A Glossary of Bike Frame Measurements
- Top Tube Length (TT): The length of the top tube from the head tube to the seat tube, which is the main frame component that supports the rider’s weight.
- Effective Top Tube Length (ETT): The horizontal distance from the center of the head tube to the center of the seatpost.
- Reach: The horizontal distance from the center of the bottom bracket to the center of the head tube.
- Stack: The vertical distance from the center of the bottom bracket to the center of the head tube.
- Head Tube Length: The length of the head tube, which houses the fork steerer and headset.
- Head Angle (HA): The angle of the head tube in relation to the ground, which affects the handling and stability of the bike.
- Seat Tube Length (ST): The length of the seat tube, which supports the seat post and saddle.
- Seat Angle (SA): The angle of the seat tube in relation to the ground, which affects the rider’s positioning on the bike.
- Bottom Bracket Height: The height of the bottom bracket, which is the pivot point for the crankset and pedals.
- Chainstay Length (C): The length of the chainstays, which connect the bottom bracket to the rear wheel.
- Wheelbase (WB): The distance between the front and rear axles of the bike.
- Stem Height: The height of the stem, which connects the handlebars to the head tube.
