To find your bike tire size, look at the sidewall of the tire. The numbers printed there, such as 700x25c or 26x2.0, tell you the tire's diameter and width. Match those exact numbers when you buy a replacement and the new tire will fit your wheel.
Tire sizing looks confusing at first, with different formats for road, mountain, and kids bikes. Once you know where to look and what the numbers mean, it takes about ten seconds to read.
This guide shows you how to measure bike tire size, how to read the sidewall numbers, and how to pick a replacement that fits the first time. It works for road bikes, mountain bikes, hybrids, and kids bikes alike.
Where do you find the bike tire size?
The size is printed right on the tire itself. Look at the side of the tire, called the sidewall, and spin the wheel until you see a set of numbers.
The numbers are usually molded into the rubber, so they can be faint on a dirty tire. Wipe the sidewall with a cloth if you cannot read them clearly.
You will often see two size formats on the same tire. Both point to the same tire, just written in different systems.
Why does the right tire size matter?
A tire that does not match your wheel simply will not fit. If the diameter is wrong, the tire will not seat on the rim at all. If the width is wrong, it can rub your frame or fork.
The right size also keeps your ride safe and smooth. A well-matched tire holds air pressure properly, grips the road, and wears evenly. Getting the size right the first time saves you a return trip and a wasted purchase.
What do the numbers on a bike tire mean?
Most tire sizes show two main numbers: the diameter and the width. The diameter is the size of the wheel the tire fits. The width is how fat the tire is.
A road tire example, 700x25c:
-
700 is the wheel diameter in millimeters
-
25 is the tire width in millimeters
-
The c is an old French sizing letter, not a measurement
A mountain bike example, 26x2.0:
-
26 is the wheel diameter in inches
-
2.0 is the tire width in inches
Road tires are usually sized in millimeters, while mountain and kids' bike tires are typically measured in inches. Once you know which sizing system your tire uses, choosing the right replacement becomes much easier. You can also Buy PEDAL Industries Bags to conveniently carry spare tubes, tools, and other cycling essentials on every ride.
What is the ISO or ETRTO number?
You may also see a smaller set of numbers like 25-622 or 54-559. This is the ISO size, sometimes called ETRTO, and it is the most exact way to size a tire.
The first number is the tire width in millimeters. The second is the bead seat diameter, which is the true rim size the tire clamps onto. When two tire labels confuse you, the ISO number settles it, because it never changes between brands.
This matters because old inch and French sizes are not always exact. Two tires both marked 26 inch can fit different rims. The ISO number removes that guesswork, so it is the safest number to shop by.
What are the most common bike tire sizes?
Different bike types use different wheel sizes. Knowing the usual sizes helps you shop faster.
-
700c: the standard for most road, gravel, and hybrid bikes
-
650b or 27.5 inch: common on modern mountain and gravel bikes
-
26 inch: older mountain bikes and many kids and folding bikes
-
29 inch: larger mountain bike wheels, also written as 700c
-
20 inch: BMX bikes and small folding bikes
Kids bikes step down through 12, 14, 16, 18, and 20 inch wheels as the bike gets bigger. The wheel size is usually printed on the tire and sometimes on the frame.
If you are buying for a child, the wheel size matters more than age. Two kids the same age can need different wheel sizes based on their height and leg length. Always check the tire number rather than guessing.
How to measure bike tire size by hand
If the sidewall numbers are worn off, you can measure the tire yourself with a tape measure. It takes two quick measurements.
Follow these steps:
-
Stand the bike upright against a wall so the wheel is straight
-
Measure across the wheel from one edge of the tire to the other, through the center, to get the diameter
-
Measure the width across the top of the tire tread
Write both numbers down in the same format your bike uses, inches for mountain and kids bikes, millimeters for road bikes. Take that measurement with you or match it to a size chart when you shop.
Does tire width matter?
Width changes how your bike feels. A narrow tire rolls fast and suits smooth roads. A wider tire grips better, soaks up bumps, and works well off road.
You often have room to go a little wider or narrower than your current tire. Check your frame and fork clearance first, since a tire that is too wide can rub. When in doubt, stay close to the size your bike came with.
Wider tires also pair with different rims. If you are changing width by a lot, take a look at your Buy wheelsets online to make sure the rim suits the new tire.
The sidewall also lists a pressure range in PSI. A wider tire runs at lower pressure for comfort and grip, while a narrow road tire runs higher for speed. Stay within the printed range whichever tire you choose.
How do you match an inner tube to your tire?
Inner tubes are sized to fit a range of tire sizes, so you do not need an exact match. The tube box lists a size range like 700x23-28c or 26x1.75-2.125.
Pick a tube whose range covers your tire size. You also need the right valve type, either Presta or Schrader, to match your rim. Check the old tube or the hole in your rim to see which valve you need. Carrying the best cycling accessories, such as spare tubes, tire levers, and a compact pump, ensures you're always prepared for unexpected flats on the road or trail.
Common bike tire size mistakes to avoid
A few errors trip up riders when buying new tires:
-
Reading only one of the two size formats and mixing systems
-
Ignoring the width and buying a tire that rubs the frame
-
Confusing 29 inch and 700c, which share a rim but differ in width
-
Guessing the size instead of reading the sidewall or ISO number
-
Forgetting to match the inner tube to the new tire size
When you replace a tire, replace or check the inner tube too. A tube that does not match the tire size will not seat properly. You can find matching tubes and tools in the bike parts collection.
Once you have the right size, a flat is a quick fix. See our guide on how to fix a flat bike tire to get back on the road fast. If you're unsure which frame size fits you best, check our bike size chart to choose a bicycle that delivers the right comfort, control, and riding performance.
Frequently asked questions
Where is the tire size on a bike?
It is printed on the sidewall, the flat side of the tire. Spin the wheel and look for numbers like 700x25c or 26x2.0.
What does 700x25c mean?
700 is the wheel diameter in millimeters and 25 is the tire width in millimeters. The c is a sizing letter, not a measurement.
Can I put a different size tire on my bike?
You can change width within your frame's clearance, but the wheel diameter must stay the same. A 700c wheel needs a 700c tire.
What if the numbers on my tire are worn off?
Measure the wheel diameter and tire width with a tape measure, then match those numbers to a size chart or a new tire.
Is 29 inch the same as 700c?
They share the same rim size, so yes at the bead. But 29 inch tires are wider and made for mountain bikes, while 700c usually means narrower road tires.