How To Measure A Bike Frame

Pro bike fitter Robbie Ferri shares everything you need to know to get your bike's frame sized up properly

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reviewed by Rory McAllister
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In cycling, optimal performance and comfort hinges on the perfect bike fit.

As a seasoned professional bike fitter, I’m very familiar with the crucial process of how to measure a bike frame – often overlooked in favor of generic manufacturer sizes. Beyond the enticing allure of sleek designs, understanding the intricacies of frame dimensions unlocks a personalized cycling experience.

Discover why embracing precision in frame measurement transcends the limitations of standardized sizes, empowering cyclists to attain the pinnacle of comfort and efficiency.

Measuring a bike frame is much easier than you might think, and when you know how to do it properly, it will really help when you are planning to buy a new bike so you can get the perfect new steed for your racing or adventures. 

The Reason We Measure Bike Frames

We measure bike frames for many reasons. Here’s my top three:

  1. To determine that it will be the correct size for you.
  2. To match a fit to an old bike, you might like the sizing of.
  3. To check out if rental or friends bikes will work for you. 

Not all bikes are the same, and all come designed uniquely. A good example is a 52 cm frame from one brand might be sold as a medium, while from another brand, it could be an extra small. You can easily see where this could cause problems.

What You Will Need To Measure A Bike Frame

The tools required in learning how to measure a bike frame. A Clinometer, straight level, a measuring tape, and a plumb line.
© Robbie Ferri/BikeTips

When it comes to measuring a bike frame, you are not going to need much. With modern technology, we have some very cool applications on your phone that can help. Here’s what I choose to use when it comes to how to measure a bike frame size.

  • A Pen And Paper 
  • A Tape Measure
  • A Clinometer (Phone Applications Work Great)
  • A Long Straight Level Or Straight Bar
  • A Plumb Line (Weight On A String Works Well)

If you have never used this equipment before, don’t worry. It’s much easier to use than you might think. I am going to be discussing every step. 

How To Measure A Bike Frame

Firstly, if you already have the bike model and size, I highly recommend going to the manufacturer’s website and getting the measurements from there, as they are the most accurate. It will save you a lot of time. 

Now for the main event: let’s start on how to measure a bike frame. I will go through the elements in the order I would when measuring a bike frame. 

Top Tube Length

Measuring a top tube on a classic road bike.
© Robbie Ferri/BikeTips

The first measurement we are going to take is the top tube length. This is the most common measurement for bike sizing and, in my opinion, the most important. A longer top tube will be for a taller rider than a smaller one for a shorter rider. 

How To Measure Top Tube Length

The top tube is measured horizontally from the seat tube’s center to the head tube’s center. The way to log this is to measure a straight line from the across above the bike and take the measurement from each point. It must be horizontal.

Seat Tube Length

Seat tube length diagram

Next, we have seat tube length. This is the measurement from the top of the seat tube to the center of the bottom bracket.

This can differ greatly between bike types, the road bike being quite large, the MTB fairly small, and gravel in between. Small seat tubes help keep the weight down low.

How To Measure Seat Tube Length

Measuring a seat tube on a classic road bike.
© Robbie Ferri/BikeTips

The seat tube is very easy to measure. Take the measuring tape from the top of the seat tube center to the center of the bottom bracket. Remember not to include the seat post in the measurement. 


Bike wheelbase diagram.

The wheelbase is the length between each point the wheels attach to the bike. The longer the wheelbase, the easier it is to control, but it can make it much less agile. Gravel bikes often have a longer chainstay compared to road bikes for control.

How To Measure Wheelbase

Measuring the wheelbase on a classic road bike.
© Robbie Ferri/BikeTips

The best way to measure the wheelbase is to put the bike in a stand or against a wall with the wheels as straight as you can get them with each other. Then, take the tape measure from one of the axle centers to the other. This is going to be your wheelbase measurement. 

Rear Center

The rear center (also referred to as the chainstay length) is the distance between the bottom bracket and the center of the axle on the rear wheel.

The longer the chainstay, the more control it can offer the rider on the bike. The shorter the chainstays, the more agile the bike will feel and the snappier it will corner. 

How To Measure Rear Center (Chainstay Length)

Measuring a chainstay on a classic road bike.
© Robbie Ferri/BikeTips

The chainstay length can be easily measured by taking the tape measure from the bottom bracket’s center to the rear axle’s center. It’s best to measure from these two points as often bikes have dropped chainstays for extra tire clearance. 

Front Center

Following on from the chainstay measurement, we have the front center. This is the distance between the front axle center and the bottom bracket center. The shorter, the more agile.

Racing bikes often have short front centers, but too short can cause toe overlap. 

How To Measure Front Center Length

Measuring front center on a classic road bike.
© Robbie Ferri/BikeTips

To measure the front center length, you can either remove the chainstay length from the wheelbase or measure from the front axle with the wheel straight to the center of the bottom bracket. 

Reach And Stack

Bike geometry: reach diagram.
Stack height diagram.

Now we have the reach and the stack. This heavily governs the height of the handlebars and how far they will be away from you while riding. When it comes to mountain biking it is very important and can help control when it comes to sketchy trails.

How To Measure Reach And Stack

Measuring reach and stack on a classic road bike.
© Robbie Ferri/BikeTips

The reach and stack are some of the more complicated measurements when it comes to how do you measure a bike frame. You will need the plumb line and the level or straight object for this. Put the level at the top of the headtube and go horizontally across. 

Then, drop the plumbline and take it to the center of the bottom bracket. The stack is the distance between the bottom bracket and the level. The reach is the distance between the head tube and the point where the plumbline starts.

Bottom Bracket Height And Drop

Next, the bottom bracket height and drop. It is a useful measurement on an off-road bike if your pedals are regularly hitting the ground. The height is the distance from the floor to the bottom bracket. The drop is from the front wheel axle center to the bottom bracket vertically down.

How To Measure Bottom Bracket Height And Drop

Measuring a bottom bracket height on a classic road bike.
© Robbie Ferri/BikeTips

The easiest way to measure bottom bracket height is to stand the bike straight against the wall and measure the distance vertically from the ground to the bottom bracket. This will give you your height, and we can work out the drop using this.

Then, take the tape measure to the front and measure vertically from the ground to the axle. Subtract the bottom bracket height from the floor to the axle, and you have the bottom bracket drop. 

Head Tube Angle and Effective Seat Angle

Head angle diagram.
Effective seat angle diagram.

Last but not least, we have seat tube and head tube angles. If you have very upright angles, the bike’s handling will feel very nimble. If they are more slack, you can get more control, and the bike will feel much more stable.

The effective seat angle is the angle from the top of the seatpost through the middle of the bottom bracket, relative to the floor.

It gives a better indication of the position of the rider’s hips relative to the pedals than the actual seat angle, which can be misleading if the bottom bracket is offset or the frame features a non-straight seat tube – as is often the case on full-suspension mountain bikes.

In these cases, raising or lowering the seat height will slightly alter the effective seat angle too.

How To Measure Seat Tube And Head Tube Angles

Measuring seat and head tube angles on a classic road bike.

To measure seat and head tube angles, you must take your level and put it across the bike’s front axle. Get it horizontal, then take your clinometer and point it up to the head tube. This is going to be the head tube angle. 

When it comes to the effective seat angle, the process is the same. Get it level, but this time on the center of the bottom bracket, then point the clinometer towards the top of the seat tube, and you will get the effective seat tube angle.

Ensure the bike is on a flat surface, and if you want it to be very accurate, add a ruler or length to the clinometer angle. 

A Final Thought: How To Measure A Bike Frame

Learning how to measure a bike frame is a great skill that can help you choose your next bike perfectly. It may look complicated to start with, but once you know what you’re looking for, it all makes sense much quicker. 

Thanks for taking the time to read our article. Now you know how to measure a bike frame size and much more!

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Robbie has traveled the globe as an endurance athlete and bikepacker, breaking world records and competing in international ultra-cycling events such as the BikingMan series and the Transcontinental Race. He's also worked as an ambassador for some of the industry's leading names, including Shimano and Ritchey. If Robbie's not on a bike, he's either fixing them or out walking with his dog!

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