Where to look for your tire size

Your bicycle tire size is printed on the sidewall of the tire itself — that's the curved outer edge you see when you look at the wheel from the side. Look for a series of numbers and letters stamped into the rubber. On most modern bikes, you'll see something like "700x28c" or "26x2.0". This marking tells you everything you need to know to buy a replacement or check pressure.

If the sidewall is too worn to read clearly, check the rim — the metal or plastic ring that holds the tire. Some rims have the size stamped on them as well. You can also find the tire size in your bike's manual or on the manufacturer's website if you know your bike's model and year.

Key Takeaways

  • Tire size is printed on the sidewall of the tire in a format like "700x28c" or "26x2.0", where the first number is diameter and the second is width.
  • The sidewall marking is the fastest and most reliable place to look, and you don't need any tools to read it.
  • If the sidewall is worn, check the rim itself or your bike's manual for the same information.
  • Tire sizes come in three main systems — ISO (metric), traditional inches, and French — and knowing which one yours uses matters when you buy replacements.

Understanding the three tire sizing systems

Bicycles use three different ways to label tire size, and they're not interchangeable. The most common on modern bikes is ISO metric sizing, which looks like "700x28c" or "650x47b". The first number is the wheel diameter in millimeters, and the second is the tire width. The letter at the end (a, b, or c) indicates how wide the tire is relative to that diameter — "c" is the widest, "a" is the narrowest.

Traditional inch sizing appears on older bikes and mountain bikes, written as "26x2.0" or "29x2.1". The first number is wheel diameter in inches, and the second is tire width. This system is straightforward but less precise than ISO because width can vary even with the same label.

French sizing uses a different format entirely — you might see "700x35" or "650x35c". It's less common in the United States but still appears on some road and touring bikes. If you're unsure which system your bike uses, the sidewall will show it clearly, and a bike shop can confirm if you bring a photo.

How to measure your tire if the label is completely gone

If the sidewall is too damaged to read and you can't find the manual, you can measure the tire yourself. You'll need a ruler or measuring tape. Measure straight across the tire from one outer edge to the other while it's mounted on the wheel — this gives you the diameter. Then measure the width of the tire from side to side at its widest point.

Write down both measurements in millimeters if possible, or convert inches to millimeters by multiplying by 25.4. When you visit a bike shop or search online, you can describe what you measured and they can help you match it to a standard size. Keep in mind that tire width can vary slightly between brands even with the same label, so an exact match may not exist — but a shop can recommend the closest option.

What the numbers and letters actually mean

In ISO metric sizing like "700x28c", the 700 refers to the bead seat diameter — the part of the tire that sits on the rim, measured in millimeters. This is not the same as the outer diameter of the inflated tire, which is why you can't just measure the outside and expect it to match. The 28 is the tire width in millimeters when the tire is mounted and inflated to its recommended pressure.

The letter (a, b, or c) is called the ETRTO code and indicates the width category. For a 700-diameter wheel, "700x28c" is narrower than "700x35c". This matters because a tire that's too wide won't fit in your frame or brakes, and one that's too narrow may not ride smoothly or handle well. Always check your bike's manual or frame for the maximum tire width it can accept before buying.

Finding the right replacement tire using your size

Once you know your tire size, you can search for replacements online or visit a bike shop with the number written down. Most online retailers and shops organize tires by size, so you can filter by your exact measurement. If you're buying from a general retailer, bring a photo of the sidewall marking to avoid confusion — some staff may not be familiar with bike tire sizing.

When you're looking at replacement options, you'll notice that tires with the same size label can vary in tread pattern, material, and price. A road bike tire marked "700x28c" will look very different from a gravel tire marked "700x40c", even though both fit a 700-diameter wheel. The width number tells you whether a tire will physically fit your bike, but the tread and construction tell you how it will perform.

Checking tire pressure using your size information

The sidewall also shows the recommended air pressure range, usually printed near the size marking. You'll see something like "80–130 psi" or "5–8 bar". This range is specific to that tire and width — a narrower tire needs higher pressure, and a wider tire needs lower pressure. Using the wrong pressure can cause flats, poor handling, or premature wear.

Check your tire pressure regularly with a pump that has a gauge. Most bike pumps sold today have a built-in gauge, or you can buy a separate pressure gauge for a few dollars. Inflate to somewhere in the middle of the range printed on your tire unless you have a reason to adjust — softer pressure for comfort on rough roads, firmer pressure for speed on smooth pavement.

When to ask a bike shop for help

If the sidewall is completely illegible, the rim has no marking, and you can't find your bike's manual, a bike shop can identify your tire size by looking at the wheel. Bring your bike or a clear photo of the wheel from the side, and they can tell you the size in minutes. This is worth doing before you try to measure yourself, because shops see hundreds of tires and can spot the size at a glance.

You should also ask a shop if you're unsure whether a tire size will fit your frame or brakes. Some bikes have tight clearances, and a tire that's technically the right size might not work. A shop can check this for you and recommend alternatives if needed.

Frequently Asked Questions

Can I use a tire with a different width if the diameter matches?

Only if your frame and brakes have room for it. A 700x35c tire will not fit in a frame designed for 700x28c, even though both are 700-diameter wheels. Check your bike's manual or measure the clearance between the tire and frame before buying a wider tire. A shop can help if you're unsure.

What's the difference between 26-inch and 700c wheels?

They're different sizes. A 26-inch wheel (traditional mountain bike size) has a bead seat diameter of about 559 millimeters, while a 700c wheel (road bike size) is 622 millimeters. They are not interchangeable, so you must use the exact size marked on your tire. Mixing them up is a common mistake when buying replacements.

Do I need to match the exact tire brand when replacing?

No. As long as the size matches, you can use a different brand. Different brands make tires with the same size label, and they'll fit the same wheel. The tread pattern and durability may differ, but the physical fit will be correct. Read reviews or ask a shop for recommendations if you're trying a new brand.

What if my tire says two different sizes?

Some older or specialty tires show both ISO and inch sizing on the same sidewall — for example, "700x28c (28x1-1/8)". Both numbers refer to the same tire, just in different measurement systems. Use whichever format is easier for you when ordering a replacement.

Can I use a narrower tire than what's marked on my bike?

Only if your frame has enough clearance and your brakes can accommodate it. A narrower tire will fit a wheel designed for a wider tire, but you need to check that the frame and brake pads won't rub. Consult your manual or a bike shop before making the change, because some bikes have very tight tolerances.