Easy Tips On How To Measure Bike Frame

How To Measure Bike Frame: A Complete Guide

You must be aware of the frame size if you want to acquire a new bicycle or sell one that has been gathering dust in your garage. By measuring a bike before you buy one, you can get one that fits your physique and is comfortable for you to ride. Mastering the tips on how to measure bike frame so that potential purchasers can be certain the bike will fit them comfortably.

The Short Answer To Finding The Proper Size Bike

Find the chart on the manufacturer’s website by searching for the recommended frame size for your height. Then, purchase that frame. nice and simple You’re also likely to receive a nice fit if your size falls in the middle of the range.

You will need to choose whether to size up or down, though, if you are closer to the size cutoff. In general, we would size down because a frame that is just a little bit too small causes less trouble than a frame that is too big.

What Is Required To Measure A Bicycle Frame

  • A measuring tape
  • A clinometer for calculating angles (there are free smartphone apps you can download)
  • Lengthened spirit level (or you can use the clinometer app and a straight piece of wood)
  • The plumb line (or you can improvise with string and a couple of blobs of Blu Tack)

Although the majority of manufacturers now size both road and mountain bikes in metric measurements, you may still come across those that do so. Some companies, like Moots, even combine the two!

To maintain consistency, we strongly advise that you stick with metric measurements. If you absolutely must, you can convert centimeters to inches by multiplying them by 2.54.

On a maker’s website, you can typically find a geometry chart for every size of a current frameset. It is worthwhile to make a copy of this if your bike is still in production because it will be more exact than your measurements and probably come in useful in the future.

How To Gauge The Drop Of Bottom Support

The drop of the bottom support is the difference between the axle height and the centerline of the crankshaft.

You can find the height of the rear axle and the height of the bottom bracket by subtracting one from the other. This is another key indicator cited by bicycle brands on geographical maps.

How to measure the height of the bottom support

Demonstration of bicycle frame bottom bracket height measurement

Measure the height of the bottom support.

Finally, the height of the bottom support is the distance from the ground to the center of the support shell. So it’s easy to measure, although be careful to keep your bike straight to get an accurate reading.

Unlike the lower bracket, it will be affected by your tires (slightly), so inflate them to your usual running pressure.

Now you have all the sizes you need. Put your number in a safe place: you don’t want to repeat the process.

How To Gauge The Length Of A Top Tube

Back then, all bicycles had horizontal top tubes. Now, the upper tubes of many bicycles will be slanted.

The actual top-tube length will typically be listed in a bike geometry table. The horizontal top tube length, also known as the effective top tube length or virtual top tube in many geo charts, must be measured for a reliable measurement, independent of the top tube angle.

That is the horizontal separation between the seatpost centerline and the head tube centerline. In order to confirm that your measurement is truly horizontal, you must use your spirit level or the clinometer app.

Many manufacturers size road bikes based on the length of the pipe jacking. Not so for mountain bikes, where frame sizes are usually marked s, M, L, etc. This is also the system used by some road bikes: Road bikes in Merida go through S, S /M, M/L and L.

Of course, the size depends on how each brand interprets it — The Ridley S-size frame has a tube of about 54 centimeters at the top, the equivalent of many brands of medium size frames.

It is important to note that not all brands measure the virtual pipe jacking length in the same way.

For example, Colnago records the horizontal distance from the head tube to the vertical line projected upward from the top of the seat tube, so it does not take into account further back projections of the seat lever, which will be smaller than other manufacturers’ numbers. A 50 second Colnago is equivalent to a 54 cm pipe jacking.

How To Gauge The Length Of A Chainstay

The length of your chainstays, which is one of the two parts that make up your wheelbase, greatly affects how your frame handles. Generally speaking, a frame with shorter chainstays will feel more lively than one with longer stays.

The chainstay length may be measured with a ruler since it is the straight line distance between the center of the bottom bracket axle and the center of the rear dropout.

How To Gauge The Length Of A Seat Tube

The length of the seat tube is measured in a straight line from the bottom bracket’s center to its top.

It’s challenging to compare the dimensions of one bike to those of an alternative because certain bikes, like the Trek Madone, have a significant extension of the seat tube above the top tube junction while others have a seat mast.

Additionally, the seat tube on mountain bikes in particular frequently has a kink, so you don’t want to follow the line of the tube itself, which will be longer.

If you’re unsure whether you’re following the correct line, align your straight edge with the center of the bottom bracket and the top of the seat tube and measure along this.

Read about: What Size Bike For 7-Year-Old: Finding The Right Size – Bike Your Best

How Are Extensions And Stacks Measured

So we’ve seen that the jacking and seat lengths are a bit of a minefield if you want to compare frames. To be more consistent, most manufacturers will now display arrival and stack values for their bikes.

They have the advantage of being independent of frame design and measuring the vertical distance between two key contact points: the bottom bracket and the top of the head tube.

We’ve published a more detailed explanation of why Reach and Stack are important.

In short, distance is the horizontal distance between the two. To measure it, you need to recalibrate your mental level.

Tie the plumb line to the end of the horizontal line. If you are using blue Tack, make sure the blob is fairly symmetrical at the end of the string and your string falls down, otherwise your measure may be off.

Align the upper edge of the horizontal line with the center line at the top of the head tube. Then move the level back and forth until the plumb line intersects the center of the spindle of the bottom bracket. Now all you need to do is measure the distance between the top of the plumb line and the head of the tube.

Another way is to lean your bike against a wall, measure the distance between the top of the head tube and the distance between the bottom bracket, and subtract the two. You still need to make sure your measurements are horizontal.

Stack is the vertical distance between the bottom bracket and the top of the head tube. So once you’re ready to record your reach range, you should also be able to measure your stack along the plumb line.

Another way is to measure the vertical distance from the ground to the top of your head tube, then measure the height of your bottom bracket from the ground and subtract this.

Reaching and folding are very difficult to capture; If you use the plumb line method, you may need another pair of hands, which is worth repeating to make sure you are consistent.

Easy Tips On How To Measure Bike Frame
Easy Tips On How To Measure Bike Frame

How Is The Front Center Measured

Another component of the wheelbase is the front center. This is equivalent to the length of the chain’s stay, but measured from axis to pre-dropout.

Again, this affects handling and the toes overlap with the front wheels. Bicycle manufacturers don’t often cite it, but BMC shows it on its geometric diagrams.

Note that the wheelbase is not the sum of the chain length and front center, as neither is measured horizontally.

How to measure the Angle between the seat tube and the head tube

Bicycle frame head tube measurement demonstration

Angle of seat to head tube. Simon Bromley / Immediate Media

The seat and head pipe angles are the two most important factors in determining machining, and a more vertical pipe Angle usually results in more flexible machining. Your dip measuring software would be useful here.

If the seat tube is straight, the Angle of the seat tube can be measured by lining up your smartphones and reading the numbers on the inclinometer app. Make sure your bike is vertical and standing on a level surface to get an accurate reading.

If your seat tube is knotted, you need to use a straight edge along the line between the bottom bracket housing and the top of the seat tube, and point this line at the phone.

Most newer bikes will have a tapered head tube, so the Angle of the head tube will not equal the Angle of its centerline.

You can hold the phone close to the latter at the center line Angle, or align the top and bottom center of the head tube with the straight edge.

If you have straight fork legs without an Angle in their crown, the Angle of the leg will be the same as the Angle of the head tube, so you can measure this instead. It’s also important to position your bike vertically.

You can also measure the Angle of the head tube by arranging the inclination Angle to expand above the steering tube.

How Is The Calculating Wheelbase Measured

The distance between the front and rear axles of your frame is its wheelbase. It affects the ride quality of a frame significantly and varies with frame size.

It’s not too difficult to measure, but you must place the fork straight ahead for an accurate reading.

Similar to reach and stack, it is important to perform the measurement numerous times to ensure that you have the same result. Additionally, accuracy will be improved if you measure the wheelbase on both sides of the bike and average them because this will account for any fork slant.

Why Is It So Difficult

As you can tell, things are starting to get complicated. We haven’t even lowered the bottom bracket or the angle between the head and the seat tube, not yet. Basically, the geometric structure of the bicycle frame is composed of many numbers, some of which are real numbers and some of which are imaginary numbers. These numbers are floating and meaningful only when they are related to a fixed point, which is the only bit that cannot be adjusted, that is, the center of the bottom bracket.

To increase the difficulty, the design and measurement of the frame are different. Take a standard frame with a normal seat back collar that protrudes about an inch above the top tube. How would you describe the length of its seat tube with the rear clip of the bike integrated with the washing seat? The position of the saddle will end in the same place, but the length of the tube frame will be greatly different.

Some companies also deliberately measure the frame in a fuzzy way, such as from the back of the head tube rather than the middle. The frame size needs to be accurate to about one centimeter. You can see how easy it is to be twisted.


Everything should be so easy, but occasionally it feels like the cycling business is purposefully attempting to make things difficult. Finding the appropriate size bike can be simple, but it can also be a huge hassle. The fact that not all bike manufacturers measure or label their frame sizes, in the same way, has a lot to do with this.

Therefore, even though you may believe that all you need to do is determine the frame size you require, then look for a model that matches, there are still a few criteria to narrow down first.

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