Bicycle Wheel Sizes – Calculator, Charts, Standards (English, French, ETRTO), How to Measure Wheel Diameter

Bicycle Wheel Sizes (Calculator)

Measure the wheel (tire) diameter and rim diameter, enter them into the calculator, and it will display the approximate tire width, wheel circumference, recommended internal rim width, and matching sizes across different international bicycle sizing standards. You can also switch between standards, and the values will update accordingly.

Calculator Notes:

According to ISO 5775, the wheel diameter should equal the rim width plus twice the tire width. This allows calculating tire width if both wheel and rim diameters are known. However, in practice, the diameter may be slightly smaller, especially if the tire tread is worn.

Rim diameter: The calculator includes standard rim diameters ranging from 203 to 635 mm. This refers to the bead seat diameter (the inner diameter where the tire fits). The actual external rim diameter is slightly larger due to the bead walls. To estimate, subtract 12-14 mm from the external diameter and find the closest value in the dropdown list. If multiple values are close, it’s better to measure both the rim and bead wall height more precisely.

Tire width: The calculator uses the nominal tire width. Actual width may vary depending on whether the tire is mounted on a narrower or wider rim than what the manufacturer used for testing.

Wheel circumference is calculated using the formula: [wheel diameter] × 3.14 (π). If you’re setting the value in a bike computer, note that the actual circumference is typically about 10% shorter due to tire compression under rider weight. For more accurate results, mark one full wheel rotation on the road under load and measure the distance, or use the Drivetrain Calculator, which lets you account for tire deflection.

Tires can typically be mounted on rims with an internal width between 30% and 90% of the tire width, depending on the priority: for better grip – 50-70%, lighter rims – 35-50%, improved aerodynamics or support at low pressure – 70-85%. The calculator’s recommended rim width (internal width between bead hooks) is based on typical usage scenarios, avoiding extreme widths.

You may also find useful:

• Bicycle riding simulation calculator
• Component Compatibility Calculator (Rear Derailleurs, Shifters, Cassettes)

Main Standards

Currently, there are three main systems for bicycle wheel (tire and rim) sizing:

• English (in inches – 29×2.3, 27.5×2.125, etc.) – mainly used on mountain bikes
• ETRTO (ISO 5775) – a unified international and more precise standard for all bicycle types
• French (700x28C, 650x42B, etc.) – primarily for road bike wheels

The English and French systems are less precise and indicate approximate sizes. That’s why tires are usually labeled in two (sometimes three) systems: inches and ETRTO, or French and ETRTO.

English Standard (Inches)

The inch-based system (1 inch = 25.4 mm) originally referred to the approximate outer diameter of the wheel (with a standard tire) and the tire width. For example, a 26×2.0 tire has an outer diameter of about 26 inches (660 mm).

However, as tire widths diverged greatly, the actual wheel diameter no longer correlates well with the listed size. A 26″ tire that is 1.0″ wide may have a diameter of about 24″ (609 mm), while a 5.05″ tire could reach 32″ (815 mm).

As a result, inch-based sizes became tied more to the rim diameter than to the actual wheel diameter. A 29″ (or 28″, with a narrower tire) wheel usually means a 622 mm rim. 27.5″ corresponds to 584 mm, 26″ to 559 mm, etc. But this isn’t always the case – a 26″ tire might fit a 584 or 590 mm rim, so it’s important to double-check.

Tire width is also not always accurate, and two 1.75″ tires from different brands may differ or even be incompatible. Officially, 1.75″ equals 44.5 mm, but such tires are often labeled as 47 mm.

This lack of consistency led to the adoption of the more standardized ETRTO system.

European or International Standard – ETRTO (ISO 5775)

ETRTO (European Tyre and Rim Technical Organisation), in cooperation with ISO (International Organization for Standardization), developed a unified bicycle tire and rim standard – ETRTO (or ISO 5775). It uses millimeters to specify the tire width and the bead seat diameter (rim diameter): 28-622, 57-584, 100-559, etc.

While the other standards allow for some manufacturer variation, ETRTO is more precise and is the most reliable system to follow. It is usually listed alongside inch-based or French sizing.

Even with ETRTO, the tire width can vary depending on rim width. Increasing the rim width by 1 mm can widen the tire by about 0.4 mm. For instance, a 57-584 tire on a 19 mm rim may actually measure around 54 mm wide, and around 59 mm if mounted on a 32 mm rim. Tire height and thus overall wheel diameter usually remain unchanged.

French Standard

The French system first lists the approximate wheel diameter, then the tire width. Sizes are in millimeters and include a letter that historically indicated tire width (from narrow to wide – A, B, C, D), though now the letter more often identifies the rim diameter. For example, 700A corresponds to a 642 mm rim (now obsolete), 700B to 635 mm, 700C to 622 mm, and 700D to 587 mm (rarely seen today).

Today, the most common sizes are 700C (622 mm) and 650B (584 mm).

The actual wheel diameter and tire width may vary. For example, a 700x40C tire might have an ETRTO marking of 42-622, meaning it is about 42 mm wide and has a total wheel diameter of around 706 mm.

Where to Find the Wheel Size on a Bicycle

The easiest way to determine the wheel size is by checking the marking on the tire. In this case (see the photo below), the marking 57-559 follows the ETRTO standard, with the size in inches indicated in parentheses – 26×2.25.

Sometimes the inch-based sizes can be more complex, for example, 16×1 3/8×1 1/4 (approximate wheel diameter 16 inches, tire height 1 3/8″, width 1 1/4″). You might also come across the French sizing system (e.g., 700x32C, 650x56B, 650Bx41, etc.).

Tires for kids’ bikes or strollers may use a slightly different format. For instance, 260×55 (approximate outer diameter 260 mm, width about 55 mm) or 280×45-203 (same principle, but with the rim diameter — 203 mm — also listed).

How to Properly Measure a Bicycle Wheel Diameter

You can measure the wheel diameter using a regular tape measure. The challenge is that it’s hard to place the tape directly along the wheel, and eyeballing it can introduce errors. A better method is to place the wheel between a wall and a box or other straight-edged object and measure the distance between them. In the photo, the wheel is a 57-559, and its calculated diameter is 673 mm (57 + 559 + 57). If the tire is worn, the actual diameter will be slightly smaller.

However, what’s more important is accurately measuring the Bead Seat Diameter (BSD), which determines whether a tire will fit the rim correctly.

• In the ETRTO system, tires are marked as: [tire width]-[bead seat diameter].
• Rims are labeled: [bead seat diameter]x[internal rim width].

These values are enough to determine tire and rim compatibility. The BSD must match, and the internal rim width should be about 30-90% of the tire width. If the rim is too narrow, the tire will have an overly rounded profile, reducing road contact. If the rim is too wide, it makes the tire profile squarer and heavier, which negatively affects handling. That’s why it’s usually best to stay within midrange values.

For example, a 60-584 tire can be mounted on a rim with a width between 18 mm (60 × 0.3 = 30%) and 54 mm (60 × 0.9 = 90%), though a width of around 30–35 mm is generally ideal, and the bead seat diameter must be 584 mm. Or, on a 622×19 rim, you could theoretically mount tires with a BSD of 622 mm and width from 21 mm (19 ÷ 0.9) to 63 mm (19 ÷ 0.3), if they fit.

To find the bead seat diameter, hook the tape measure about 5-7 mm from the edge of the rim and measure to the hub axle. Multiply this value by 2 to get an approximate BSD. In the photo, the result is about 560 mm (280 × 2), and based on standard BSD values, the closest ones are 547, 559, and 571 mm – so 559 mm is the best match.

For more accurate results, remove the tire, measure the rim wall height, and then measure the total rim diameter just like we did for the wheel:

The calculation gives: 573 – 7 × 2 = 559 mm.

Bicycle wheel size chart

In the table below, you can see the correspondence of wheel sizes in American, International and French standards, and on which bikes they are commonly used.

This table lists popular wheel sizes and their specifications:

If you couldn’t find your wheel size in the calculator or have any questions, feel free to ask in the comments.