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

Bicycle Wheel Sizes (Calculator)

Set the wheel size in any standard (ETRTO, inches, or French) and the calculator will show the equivalents in the other standards, as well as the calculated (may differ slightly from actual values due to tread wear or rim width) wheel diameter, rim diameter, tire width, recommended rim width range, and wheel circumference (accounting for tire deflection under weight – for a bike computer).

Alternatively, if you don’t know the standard and size (for example, the marking is unreadable), you can measure the outer diameter of the wheel (tire) and the bead seat diameter of the rim (how to do this is described below), enter them into the calculator, and it will show the matching wheel sizes across the different bicycle marking standards.

You may also find useful:

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

Calculator notes:

According to the ISO 5775 standard, the wheel diameter should equal [rim diameter] + ([tire width] * 2). In practice, however, the diameter may be slightly smaller if the tire tread is worn.

Rim diameter. The calculator lets you choose the main standard rim diameters from 203 to 686 mm. This is the bead seat diameter (the diameter of the inner part of the rim on which the tire sits), so on the outside, taking the flange height into account, the rim will be slightly larger. You can subtract 12–14 mm from the outer rim diameter and select the closest value in the dropdown list. But if there are several close values nearby, it’s better to measure the rim and flange height more precisely.

Tire width. The calculator uses the nominal tire width in its calculations. The actual width may be slightly smaller or larger if the tire is mounted on a narrower or wider rim than the manufacturer used for measurements.

Wheel circumference is calculated using the formula: [wheel diameter] * 3.14 (Pi). If you need to set the circumference in a bike computer, the resulting value won’t be entirely accurate, because the tire compresses under the rider’s weight (usually by about 10%). So, for a more precise value, you can make 2 marks on the road for one wheel revolution under your weight and measure the distance between them, or set the tire deflection/compression percentage in the calculator. At 0%, the circumference is calculated without accounting for compression, as if the tire were perfectly rigid.

A tire can be mounted on a rim with an internal width of roughly 30% to 90% of the tire width (depending on your priorities: for better road grip – 50–70%, to reduce rim weight – 35–50%, to improve wheel aerodynamics or increase air volume and provide better sidewall support at low pressure – 70–85%). In the calculator, the recommended rim width (internal width between the flanges) is calculated based on the likely use case of the bike, without extremely narrow or wide values.

Main standards

Today there are 3 main standards for marking bicycle wheels (tires and rims):

• American or 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 wheels of all types of bicycles
• French (700x28C, 650x42B, etc.) – for road bike wheels

The American and French standards are less precise and indicate an approximate size. That’s why tires are usually marked in two (or even three) standards at once: in inches and ETRTO, or in the French system and ETRTO.

English Standard (Inches)

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

But later, tires with vastly different widths began to be made, and now the wheel size in inches is completely unrelated to the actual diameter. That same 26 wheel with a 1.0″ tire will have a diameter of about 24 inches (609 mm), and with a 5.05″ tire – about 32 inches (815 mm).

In practice, it turned out that the main wheel sizes in the American system, not in the most obvious way, became tied more to the rim diameter than to the wheel diameter. A 29-inch wheel (or 28″ if a narrower tire is fitted) is a rim with a diameter of 622 mm, 27.5 inches – 584 mm, 26 inches – usually 559 mm, etc. But this isn’t always the case, and a 26-inch tire could be, for example, for a 584 or 590 mm rim, so this always needs to be checked.

As for tire width, things aren’t smooth here either, and tires of the same size from different manufacturers may differ (or sometimes even be incompatible), and the width itself is calculated quite approximately. For example, 1.75″ in millimeters should be 44 (1.75 * 25.4), but in practice tires 47 mm thick are traditionally marked this way.

That’s why the ETRTO standard was created to bring everything to uniformity.

European or international standard – ETRTO (ISO 5775)

ETRTO (the European Tyre and Rim Technical Organisation), together with ISO (the International Organization for Standardization), developed a unified standard for marking bicycle wheels – ETRTO (or ISO 5775). It indicates the tire width and its bead seat diameter (which should match the rim diameter) in millimeters – 28-622, 57-584, 100-559, etc.

While in other standards manufacturers may allow some tolerances when specifying sizes, ETRTO is more precise, and it makes sense to rely on it first and foremost. It is usually listed in addition to the wheel size in inches or in the French standard.

But even in ETRTO, the tire width can be slightly larger or smaller depending on the rim width. Increasing the rim by 1 mm increases the bicycle tire width by about 0.4 mm. For example, a 57-584 tire on a rim with a 19 mm internal width will be about 54 mm, and if mounted on a 32 mm rim – about 59 mm. At the same time, its height and, accordingly, the wheel diameter do not change.

French standard

In the French standard, the approximate wheel diameter is written first, followed by the tire width. The size is given in millimeters, and the marking includes a letter that used to denote the tire width (from narrow to wide – A, B, C, D); nowadays the combination of the approximate wheel diameter with the letter defines the rim diameter. For example, 700A is a rim with a diameter of 642 mm (an obsolete size), 700B – 635 mm, 700C – 622 mm, 700D – 587 mm (practically no longer found), etc.

Nowadays 2 sizes are mainly used – 700C (622 mm) and 650B (584 mm).

At the same time, the actual wheel diameter and tire width may vary. For example, a 700x40C tire may have the ETRTO marking 42-622, i.e. its width will be about 42 mm and the wheel diameter – about 706 mm.

Where the size is written on a bicycle wheel

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

Sometimes inch sizes can be more complex, for example, 16×1 3/8×1 1/4 (approximate wheel diameter 16 inches, tire height 1 and 3/8 inches, width 1 and 1/4 inches). The size may also be given in the French standard (700x32C, 650x56B, 650Bx41, etc.).

Tires for children’s bikes or strollers may be marked slightly differently. For example, 260×55 (approximate outer tire diameter 260 mm, width about 55 mm) or 280×45-203 (the same principle, but the rim diameter is additionally indicated – 203 mm).

How to correctly measure a bicycle wheel diameter

You can measure the wheel diameter with an ordinary tape measure. The difficulty here is that it’s hard to place it directly against the wheel, and eyeballing the measurements can introduce error. So it’s better to place the wheel between a wall and some box or rectangular object and measure the distance between them. In the photo the wheel is 57-559, its calculated diameter is 673 mm (57 + 559 + 57). If the wheel isn’t new and the tread is worn, its diameter will be smaller than the calculated one.

However, it’s more important to correctly measure the bead seat diameter (BSD – Bead Seat Diameter), because tire and rim compatibility depends on it.

• In ETRTO, tires are marked as follows: [tire width]-[bead seat/inner diameter of the tire].
• Rims: [rim bead seat diameter]x[internal rim width].

These parameters are enough to determine whether a tire and rim are compatible or not. For compatibility, their bead seat diameters must match, and the internal rim width should be within a range of roughly 30–90% of the tire width. But with values that are too low, the tire will have worse road contact due to an overly rounded tire profile, and with values that are too high, the rim will be heavier and the tire profile shape will become closer to a square, which also negatively affects handling. So it’s usually better to stick to some mid-range figures.

For example, for a 60-584 tire you can use a rim with a width from 18 mm (30%, 60 * 0.3) to 54 (90%, 60 * 0.9), although it’s usually better to stick to mid-range values (~30–35 mm), and with a bead seat diameter of 584 mm. Or on a 622×19 rim you can theoretically fit tires with a bead seat diameter of 622 and a width from 21 mm (19 / 0.9) to 63 mm (19 / 0.3), if it fits.

So, to find out the bead seat diameter, you can place the tape measure hook on the rim, stepping back about 5–7 mm from the edge, and measure the distance to the center of the wheel axle. The result is multiplied by 2 to give the approximate bead seat diameter. In the photo it came out to about 560 mm (280 * 2), and if you look at the rim diameters in the calculator, the closest values are 547, 559, and 571, so the most suitable one is 559.

To take more precise measurements, you need to remove the tire, measure the flange height and the rim diameter the same way we measured the wheel diameter:

The result was 573 – 7 * 2 = 559 mm.

Bicycle wheel size chart

In the table below you can see the correspondence between wheel sizes in the American, international, and French standards, as well as which bikes they are usually used on.

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.