Measure wheel diameter with a tape measure or ruler

The most common measurement is wheel diameter — the distance across the wheel from one edge of the tire to the opposite edge, passing through the center. Lay the bike on its side on a flat surface. Place a tape measure or ruler across the tire at its widest point, making sure it passes through the center. Read the number where it meets the opposite side. Most adult bikes measure 26, 27.5, or 29 inches in diameter. Children's bikes are often 20 or 24 inches.

If you cannot fit a tape measure across the wheel, measure the radius instead — the distance from the center of the wheel to the outer edge of the tire — and multiply by two. This gives you the diameter. Write down the number in inches; it is the first piece of information you need when buying replacement tires or wheels.

Key Takeaways

  • Wheel diameter is measured across the tire from edge to edge through the center, and most adult bikes use 26, 27.5, or 29 inches.
  • Rim width is the measurement of the metal wheel itself, separate from the tire, and ranges from about 13 to 25 millimeters on most bikes.
  • Tire width is printed on the sidewall of the tire itself in the format 700x35c or 26x2.0, where the second number is the width.
  • You need all three measurements — diameter, rim width, and tire width — to order the correct replacement tire or wheel.

Find rim width by measuring the metal wheel itself

Rim width is the width of the metal wheel, measured from the inside edge to the inside edge where the tire bead sits. This is different from the tire width. To measure it, you need to remove the tire and measure the rim directly with a caliper or narrow ruler. Place the measuring tool across the rim from one inner edge to the other. Most road bike rims measure 13 to 17 millimeters wide. Mountain bike and gravel bike rims are typically 19 to 25 millimeters wide.

If you do not want to remove the tire, you can often find the rim width printed on the rim itself in small text, or look up your bike's specifications online using the brand and model number. The rim width matters because it affects how the tire sits on the wheel and how the bike handles.

Read tire width from the sidewall marking

The tire width is printed directly on the side of your tire and is the easiest measurement to find without tools. Look for a marking like 700x35c (road and gravel bikes) or 26x2.0 (mountain bikes). The second number is the width. On road tires, the width is given in millimeters — so 700x35c means 35 millimeters wide. On mountain and hybrid tires, it is often given in inches — so 26x2.0 means 2.0 inches wide, which equals about 51 millimeters.

The first number in the marking is the wheel diameter. So a 700x35c tire fits a 700c wheel (which is 29 inches in actual diameter) and is 35 millimeters wide. A 26x2.0 tire fits a 26-inch wheel and is 2.0 inches wide. Write down both numbers exactly as they appear on the tire.

Understand the difference between wheel size standards

Bicycle wheel sizes use different naming systems depending on the type of bike. Road bikes use the 700c standard, which is actually 622 millimeters in rim diameter but is called 700c for historical reasons. The actual tire diameter is about 29 inches when inflated. Mountain bikes use 26-inch, 27.5-inch, or 29-inch wheels, which are measured in actual inches. Gravel and hybrid bikes often use 700c as well, though some use 27.5 inches.

This matters because a 700c tire will not fit a 26-inch wheel, even though both are close in size. Always match the tire size marking to your wheel size exactly. If you are unsure which standard your bike uses, measure the diameter as described above, or check your bike's manual or the manufacturer's website.

Measure spoke length if you are building or rebuilding a wheel

If you are replacing spokes or building a wheel from scratch, you need to know the spoke length. This is measured from the hole in the hub (the center of the wheel) to the hole in the rim where the spoke threads in. The easiest way is to remove one spoke and measure it with a tape measure from the inside of the hub flange to the tip of the spoke. Spoke length is given in millimeters and typically ranges from 260 to 310 millimeters depending on the wheel size and hub width.

If you do not want to remove a spoke, you can measure the distance from the hub center to the rim and use an online spoke calculator, entering your wheel diameter, hub width, and rim diameter. Most bike shops can also measure spokes for you if you bring the wheel in.

Use calipers for the most accurate measurements

A digital caliper is the most accurate tool for measuring rim width and other small dimensions. It costs between $10 and $30 and measures to within a millimeter. To use one, open the jaws, place the rim between them, and close gently until the jaws touch both inner edges of the rim. Read the digital display. Calipers are especially useful if you are ordering a replacement rim or checking whether a tire will fit your existing rim.

For wheel diameter and tire width, a tape measure or ruler works just as well and costs less. Keep your measurements written down — take a photo of the tire sidewall marking and write down the diameter and rim width. This information is what you need when buying new tires, tubes, or wheels.

Frequently Asked Questions

What is the difference between wheel size and tire size?

Wheel size is the diameter of the rim itself, measured in inches or millimeters. Tire size includes both the wheel diameter and the tire width. A 26-inch wheel can accept tires of different widths — 26x1.95, 26x2.0, or 26x2.1 — but they all fit the same 26-inch rim.

Can I put a wider tire on my bike?

It depends on your frame and fork clearance. Measure the space between the tire and the frame or fork when the wheel is in place. If you have at least 5 millimeters of clearance on each side, you may be able to fit a slightly wider tire. Check your bike's manual for the maximum tire width the frame is designed for, or ask a bike shop to measure the clearance for you.

What does the letter at the end of a tire size mean?

On road tires, letters like "c" in 700x35c refer to the bead seat diameter — the part of the tire that hooks onto the rim. Most road tires use the "c" standard. Mountain and hybrid tires do not use letters. The letter matters when ordering replacements, so include it in your measurement.

Do I need to measure both wheels?

Both wheels on a bike should be the same size, so measuring one is usually enough. If you are replacing a tire and want to be certain, measure both to confirm they match. Mismatched wheel sizes can affect how the bike handles and brakes.