How To Measure A Road Bike Frame:

Looking to buy yourself a road bike and wondering what frame size is best for your height?

When buying a new bike, understanding the key measurements that define your bike frame size is super important to ensure the road bikes you’re looking at are the right match for you and your riding style

Or even if you’re thinking of renting a bike, knowing the right measurements fit your body will ensure that your ride is comfortable and you have the right road bike sizing.

Now, wait, let me tell you something.

Not all manufacturers design their bikes in the same way, so by understanding all the key measurements, so you’re comparing oranges to oranges and not apples to pears.

But don’t worry, I’m here to guide you through it all; it may seem confusing at first, but this simple guide should help clear things up, so you know how to read a road bike size chart or any size chart for that matter.

So stay tuned; you won’t want to miss this.

how to measure bike frame

How To Size A Road Bike

Measuring a classic road bike frame size is pretty simple.

All you really need to do is find the top of the seat tube (where the seat post is held). Find the center of the bottom bracket (which holds the crank arms together) and measure the distance between these two points.

You can then record these measurements and compare the bike frame size chart to find your perfect bike.

How To Measure Adult’s Size Bike:

Now you need to measure yourself to work out what would work best based on the road bike sizing chart. Adult bike sizes are measured on both height and inseam size.

What is an inseam size, you may be wondering?

The Inseam size is the measurement from the bottom of your inside leg to the top of your leg where your crotch is. Measuring the inseam is fairly easy; it only really requires two people and a book.

  • Stand with your back against the wall, spine up, and raise the book until it mimics a bike seat and is positioned between your leg.
  • Then get the second person to measure the top of the book to the floor; this will be your inseam length.

Or, if you prefer, you can always go into a bike store and have a professional bike fit done for you; this will also make results much more accurate, especially if you’re unsure how to measure the inseam.

Then based on your inseam length, this is the average road bike size, so you can choose your very best fit based on these measurements.

Height  Inseam  Average Size Road Bike
5’4 – 5’8″ 27″ – 29″ inseam Small (49 – 52 cm)
5’8 – 5’10” 29″ – 31″ inseam Medium (52 – 56 cm)
5’10″ –  6″ 31″ – 33″ inseam Large (54 – 58 cm)
6′ to 6’3 33″ – 35″ inseam Extra Large (56 – 61 cm)

But if you are wondering what the bike size chart is for mountain bikes, here is the sizing. A mountain bike frame is slightly different as the wheelbase is often larger, and the seat post is often tilted. 

It follows a similar sizing chart to regular road bikes but bear in mind a few different measurements just to be sure you’re getting the right fit for you.

How To Measure A Kid’s Bike

Buying the right frame for your child is crucial; it helps provide comfort, stability, and safety when your child is riding. But how do you measure a child’s bike size?

The easiest way to measure your child’s bike size is by taking them into the store and letting them try out a variety of different bikes, so they can find one that’s comfortable for them.

Or you can buy online, I personally love Woom Bikes as they offer a variety of different road bike sizes for your child, plus all their bikes are adjustable in lots of places, so the bike grows with your kid.

So all you need to do is measure the height of your child. First, the size of children’s bikes is based on the wheel diameter rather than by frame.

Wheel Size  Age Height Inseam
12 inches 2-3 2’10 – 3’4″ 14-17″ or 35-42 cm
14 inches 3-4 3’1 – 3’7″ 16-20″ or 40-50 cm
16 inches 4-5 3’7 – 4’0″ 18-22″ or 45-55 cm
18 inches 5-6 3’9 – 4’3″ 20-24″ or 50-60 cm
20 inches 5-8 4’0 – 4’5″ 22-25″ or 55-63 cm
24 inches 7-11 4’5 – 4’9″ 24-28″ or 60-72 cm
measure kids bike

How To Measure Top Tube Length:

If you’re planning on selling your bike, buying a new one, or buying bike parts for your road bike, then knowing the lengths of the components of your bike is super important. So let’s start with the top tube.

Older models of bikes had horizontal top tubes, but nowadays, modern models tend to have a slope. The geometry of the bike you’re looking to buy will include this.

Regardless of the top tube angle, you’ll need to measure the horizontal top tube length called either the effective top tube length or the virtual top tube length.

This will be the horizontal distance between the centreline of the head tube and the centerline of the seat post. You should use the clinometer app or a level to ensure your measurement is really horizontal.

How To Measure Seat Tube Length:

Seat tube length is the straight line distance between the center of the bottom bracket and the top of the seat tube. However, between brands, this isn’t created equal.

For example, some brands like Trek have a considerable extension of the seat tube above the top tube junction while others use a seat mast, so it’s difficult to compare.

Plus, mountain bikes tend to differ from road bikes as they tend to have a kink in the seat tube, so the tube will be longer, making it more awkward to measure.

So line up the straight edge with the bottom bracket center and the top of the seat tube and measure along this line, following the right line.

How To Measure Reach & Stack:

So now we’ve covered the top tube and seat tube lengths on the bicycle frame. Next up is the compare the reach and stack values; these are the measurements of the perpendicular distances between two contact points.

The bottom bracket and top of the head tube.

The reach is the horizontal distance between the two; measure it using a spirit level to get the accurate length. Then attach the plump line to the end of the level and let the string hand down straight.

Align the top edges of the level with the centreline of the head tube and then move the level back and forth until the plump line intersects with the center of the bottom bracket single.

Now all you need to do is measure the distance between the top of the plump and the head tube, and that’s how you measure the reach on the bike frame size.

You can alternatively push your bike up against the wall and measure the distance to the top of the head tube and the distance to the bottom bracket. Subtract one from the other, and you have your reach.

Following the plump line you’ve just measured, you can also measure your stack– this is the vertical distance between the bottom bracket and the top of the headtube.

This method can be quite technical and awkward, so if it’s easier, I would recommend grabbing an extra set of hands.

measure bike frame

How To Measure Road Bike Handlebars:

In order to measure bike handlebars, there are three factors you need to consider: the reach, width, and drop to find your perfect handlebar width.

This is super handy when buying a new bike or buying new road bike handlebars.

Reach:

The reach is the distance from the center of the handlebar at the stem to the bend– where the brake levers are mounted. This is how far your body will lean forward when riding.

You want the width to feel neutral on your spine and comfortable.

The reach can affect your upper body position when riding on the hoods without affecting your body position in the drops or tops. On average, the reach varies from 80-85mm.

Width:

The width of the bar is measured from the center of the drops to the middle. You should measure your shoulder width as the wider your shoulders, the wider the bar you should be looking at.

Wider bars offer better control, especially on daunting descents, and they offer more torque over the bike in a sprint, but if you ride with a bar that’s too wide, it can result in a sore neck and shoulders.

This is because the shock absorption is often absorbed into your arms; if it is too wide, these vibrations move up to your shoulders which can cause aches and pains.

Drop:

The drip is measured from the center of the flat top section to the center of the bar at the deepest point of the drop; a shallow drop means that your body less drastically from hood to drop– often around 125mm or less)

While deeper drops can be 130mm or more, the lower your back is, the faster you go, so you’ll find in race bikes that the drop is far deeper.

But the lower the drop, the less comfort you can achieve.

road bike frame

How To Measure Wheelbase:

The wheelbase on your bike’s frame size is the distance between the front and rear axles, it determines the bike frame’s ride quality, and it can vary with frame size too.

It’s quite easy to measure, but I would recommend repeating your measurements several times to make sure you have the right number to make sure it is accurate.

If you measure the wheelbase on both sides, then take the average as this is compensated if the fork is not quite straight.

It’s fairly easy to measure, although you need to set the fork straight ahead, or your measurement will be incorrect.

How To Measure Chainstay Length:

The chainstay length is a part of the components that make up the wheelbase and contribute to your frame’s handling characteristics. Frames with shorter chainstays will be more agile and lively.

In order to measure the chainstay length, you need to measure the straight line distance between the center of the bottom bracket axle and the center of the rear dropout.

You can do this easily using a tape measure or a ruler.

How To Measure Front Center:

The second component of the wheelbase is the front center which is similar to the chainstay length but is measured from the axle of the front dropout.

This affects the handling of the bike as well as toe overlap with the front wheel.

riding a road bike

How To Measure Bottom Bracket:

There are a couple of ways to measure the bottom bracket the drop, and the height of the bottom bracket. This can help distinguish the frame size you need for your new bike.

The bottom bracket drop is the difference between the height of the wheel axels and the centreline of the crank axle. It is fairly easy to measure.

You just need to find the height of the rear axle and the height of the bottom bracket and then subtract by each other. This is often found on the manufacturer’s geo chart.

The bottom bracket height, however is the distance from the ground to the center of the bottom bracket. So make sure your bike is straight when measuring.

Before measuring, also make sure to inflate your tires to your usual tire pressure, so the measurement is more accurate.

road bike pictures

Summary:

So there you have everything you need to know about how to choose the right bike frame size for you. Knowing these key measurements will make measuring your bike frames 10x easier and 10x better suited.

When it comes to measuring road bikes, it’s not always about finding the top quality components and bike brands– while this is important, the measurements trump it every time.

You could have the best components, best frame geometry in the world but if it isn’t the right fit for you, it’s worthless, so spend time researching and measuring your bike.

The positions and measurements will massively affect your riding position, riding comfort, and efficiency. So test ride a few before you buy and remember to get the right measurements.

Enjoy your road bike buying experience, everyone!

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