Home / Bicycle

Bike tire size chart and decoder

Type the size on your tire, in any system. See its ISO (ETRTO) size, the bead seat diameter that decides which rims it fits, and its approximate diameter. Below is the full chart of bead seat diameters.

Tire marking

Size on the tire

Not a size we can read. Try 28-622, 700x28c, 29x2.2 or 26 x 1 3/8.

Try

ETRTO (28-622), French (700x28c, 650b x 47), decimal inch (29x2.2, 26x1.95) or fractional inch (26 x 1 3/8, 27 x 1 1/4).

Bead seat diameters and their traditional names

Every bead seat diameter in Sheldon Brown's ISO cross reference (revised by John Allen). A tire fits a rim when the bead seat numbers match.

BSD (mm)	BSD (in)	Traditional markings
787	30.98	36 inch
686	27.01	32 inch
642	25.28	700 A
635	25.00	28 x 1 1/2, 700 B, 28 x 1 5/8 x 1 1/2 (old, Sweden)
630	24.80	27 x any width, except 27.5 and the 609 mm size
622	24.49	700 C, 29 inch, 28 x 1 5/8 x 1 1/2 and other pairs of numbers, 28 x 1 1/2 F.13 (Canada), 28 x decimal widths (non-standard, some German makers)
609	23.98	27 x 1 1/2 (rare Danish size)
599	23.58	26 x 1.25, 26 x 1.375 (rare, old US size)
597	23.50	26 x 1 1/4, 26 x 1 3/8 (S-6)
590	23.23	26 x 1 3/8 (E.A.3), 650 A
584	22.99	650 B, 26 x 1 1/2, 27.5 (27 five)
583	22.95	700 D
571	22.48	650 C, 26 x 1, 26 x 1 1/8, 26 x 1 3/4 (S-7)
559	22.01	26 x 1.00 to 26 x 5.0 (most mountain bikes, cruisers, fat bikes)
547	21.54	24 x 1 1/4, 24 x 1 3/8 (S-5)
541	21.30	600 A
540	21.26	24 x 1 1/8, 24 x 1 3/8 (E.5), 600 A (the French table gives 540 mm, the cross reference 541 mm)
534	21.02	24 x 1.5 (Dutch, rare)
520	20.47	24 x 1, 24 x 1 1/8, 24 x 1 3/8, 24 x 1 3/4
507	19.96	24 x 1.5 to 24 x 2.125
501	19.72	22 x 1 3/8 (British), 22 x 1.00
490	19.29	550 A
489	19.25	22 x 1 1/8 NL, 22 x 1 3/8 NL
484	19.06	550 B
457	17.99	22 x 1.75 to 22 x 2.4
451	17.76	20 x 1 1/8, 20 x 1 1/4, 20 x 1 3/8, OS 20 x 1.6, 1.75, 1.85
440	17.32	500 A
438	17.24	20 x 1 3/8 NL
428	16.85	20 x 2 (Swedish)
419	16.50	20 x 1 3/4
406	15.98	20 x 1.5 to 20 x 2.125
400	15.75	18 x 1, 18 x 1 3/8
390	15.35	450 A
369	14.53	17 x 1 1/4
355	13.98	18 x 1.5 to 18 x 2.125
349	13.74	16 x 1 3/8
340	13.39	400 A
337	13.27	16 x 1 3/8
335	13.19	16 x 1 3/8
317	12.48	16 x 1 3/4
305	12.01	16 x 1.75 to 16 x 2.125
298	11.73	14 x 1 3/8
288	11.34	350 A
254	10.00	14 x 1.75 to 14 x 2.125
203	7.99	12 1/2 x any width
152	5.98	10 x 2
137	5.39	8 x 1 1/4

Source: Sheldon Brown, Tire Sizing, sheldonbrown.com, revised by John Allen. The BSD in inches is our conversion. Rim brakes and frame clearance limit which sizes a bike can take: measure before you buy.

How bicycle tire sizes work

A bicycle tire can carry up to three kinds of size marking. The only one that tells you for sure which rim it fits is the ISO size, formerly called ETRTO. It has two numbers: the tire width in millimeters, then the bead seat diameter (BSD) in millimeters. 28-622 is a 28 mm tire for a 622 mm rim. If the second number matches your rim, the tire goes on it.

The older systems describe roughly the outside diameter of the tire: French sizes in millimeters with a letter for the width class (700C, 650B), and inch sizes (26 x 1.95, 27 x 1 1/4). These names drifted from reality as tires got narrower and wider, so one name can mean several rims.

Nominal inch sizes are ambiguous

"26 inch" is the clearest case. The source lists 559 mm (mountain bikes, cruisers), 571 mm (26 x 1, 650C), 584 mm (26 x 1 1/2, 650B), 590 mm (26 x 1 3/8 E.A.3), 597 mm (26 x 1 1/4) and 599 mm, all called 26 inch. Even 26 x 1 3/8 alone can be 590 or 597. The decoder lists every rim a marking can mean, from the Sheldon Brown charts, and asks you to check the ETRTO number.

Decimal and fraction sizes that are equal as numbers are different tires: 26 x 1.75 fits a 559 mm rim, but 26 x 1 3/4 is a 571 mm size.

The formula

approximate outside diameter = bead seat diameter + 2 × tire width
inches = mm ÷ 25.4

The source puts the tire's outside radius at about the rim radius plus the tire width, and up to 1 cm more for a deep tread, so treat the result as approximate.

Worked example: 700c to inches

A 700x28c tire is ISO 28-622. Its approximate diameter is 622 + 2 × 28 = 678 mm, or 678 ÷ 25.4 = 26.7 inches. The rim itself is 622 ÷ 25.4 = 24.5 inches at the bead seat, which is why "700" and "28 inch" are both names for it and neither is a measurement. A 29x2.2 mountain bike tire uses the same 622 mm rim: 622 + 2 × 55.9 = 733.8 mm, about 28.9 inches.

The decoder feeds the same diameter to the bike gear calculator and the bike speed calculator.

Shopping for a whole bike? See Bike frame size by height on sizeparade.com.

Questions

What is 700c in inches?

The 700C rim has a 622 mm bead seat, 24.5 inches. The tire's outside diameter depends on its width: about 26.5 in for 700x25c (672 mm), 26.7 in for 700x28c (678 mm) and 27.6 in for 700x40c (702 mm).

What does ETRTO 37-622 mean?

A tire 37 mm wide for a rim with a 622 mm bead seat diameter, the 700C size. Its outside diameter is about 622 + 74 = 696 mm.

Are 29 inch and 700c the same rim?

Yes. Both are 622 mm at the bead seat. "29 inch" is a marketing name for wide 622 mm tires, according to the Sheldon Brown charts.

Is 27.5 the same as 650B?

Yes, both are 584 mm at the bead seat. 27.5 (or "27 five") is used for wide mountain bike tires, 650B for touring and utility tires.