Inner Tube Size Charts and Conversions: How to Find the Right Bicycle Tube

To find the right bicycle inner tube, read the size printed on your tire's sidewall and match two values: the rim diameter, which must match exactly, and the tire width, which must fall inside the tube's printed width range. The most reliable marking is the ETRTO size, such as 37-622. In that marking, 37 is the tire width in millimetres and 622 is the bead seat diameter in millimetres. A tube labelled 622 with a width range of 32–47 mm fits that tire. Then choose the valve type your rim accepts, Presta or Schrader, and a valve stem long enough for your rim depth.

How do I know the size of my inner tube?

You know the size of the inner tube you need from the tire, not the tube. The tube takes the shape of the tire, so the tire sidewall markings tell you what to buy. Follow these steps.

1. Find the size on the tire sidewall. Look for a pattern like 700x28C, 29 x 2.25, 27.5 x 2.4 or 26 x 1 3/8. Most tires also show an ETRTO size such as 28-622 or 57-584, sometimes in smaller print.
2. Use the ETRTO number if there is one. The second number is the bead seat diameter (BSD) in millimetres. The tube's diameter must match it exactly.
3. Note the tire width. This is the first ETRTO number in millimetres, or the second number in an inch or 700C size.
4. Check the valve hole in the rim. A narrow hole of about 6 mm takes a Presta valve. A wider hole of about 8.5 mm takes a Schrader valve.
5. Measure rim depth at the valve hole if you have deep-section rims. You will need a longer valve stem.
6. Buy a tube whose label covers your size. It must have the same diameter, a width range that includes your tire width, the right valve type and an adequate valve length.

If the sidewall is worn and unreadable, check the label on the old tube or the sticker on the rim. A rim sticker such as 622x19 confirms the 622 mm bead seat diameter. The 19, however, is the rim's inner width in millimetres, not the tire width.

What do the numbers on the tire sidewall mean?

Bicycle tire sidewalls can show up to three size systems: ETRTO (ISO) millimetres, inch sizes and French sizes. Only the ETRTO system describes the exact rim diameter without ambiguity. The other two are nominal names that roughly describe the outer size of the tire.

ETRTO size: tire width and bead seat diameter

An ETRTO size is written as width-bead seat diameter, both in millimetres. Examples are 25-622, 57-584 and 54-559.

• Width (the first number) is the nominal tire width in millimetres.
• Bead seat diameter (the second number) is the diameter of the rim where the tire bead sits, in millimetres.

If two tires share the same second number, they fit the same rim diameter and use the same tube diameter, even when their inch or French names look different. For example, 700x35C, 28 x 1 5/8 x 1 3/8 and 29 x 1.40 all use a 622 mm bead seat diameter.

Inch sizes: decimal versus fractional

Inch sizes are written as nominal diameter x width, such as 26 x 2.10 or 26 x 1 3/8. They come in two styles, and the two styles are not interchangeable even when the first number is the same.

• Decimal widths such as 26 x 2.10, 27.5 x 2.25 and 29 x 2.4 are used mainly on mountain, BMX and children's bikes.
• Fractional widths such as 26 x 1 3/8 and 27 x 1 1/4 are used on older road, touring and city bikes.

A 26 x 2.10 tire has a 559 mm bead seat diameter. A 26 x 1 3/8 tire has a 590 mm bead seat diameter. A tube for one will not fit the other.

The first inch number is a nominal name, not a measurement. Multiplying 26 inches by 25.4 mm gives 660 mm, which is neither the rim diameter nor the exact tire diameter. Width conversions are more meaningful. A 2.25-inch width is about 57 mm (2.25 x 25.4), which is why a 27.5 x 2.25 tire is also marked 57-584.

French sizes: 700C and 650B

French sizes are written as nominal outer diameter in millimetres x width, followed by a letter. Examples are 700x25C and 650x47B. The letter originally indicated a rim size class. Today it serves as a name.

• 700C = 622 mm bead seat diameter. This is the same rim diameter as 29-inch mountain bike wheels and European 28-inch wheels.
• 650B = 584 mm bead seat diameter. This is the same rim diameter as 27.5-inch mountain bike wheels.
• 650C = 571 mm bead seat diameter. It appears on some older small road and triathlon bikes.

A 700x28C tire therefore needs a 622 mm tube rated for a width range that includes 28 mm.

Sidewall markings that are not tube size

Several other tire sidewall markings describe performance or use rather than dimensions. They do not change which tube size you need.

• Pressure range (for example 50–85 psi or 3.5–6 bar) is the recommended inflation range of the tire. Standard inner tubes are not sized by pressure.
• TPI (threads per inch) describes the density of the tire casing. It is a construction rating, not a size.
• E-bike markings such as E-25 or E-50 indicate the tire's suitability for electric bikes at the stated speed class. They are not size markings.
• Aspect ratio is normally absent on bicycle tires. Bicycle sizes assume a roughly round cross-section, so tire height is approximately equal to width. Motorcycle-style tires on some heavy e-bikes and scooters are the exception. They use markings like 120/70-12, where 70 means the sidewall height is 70% of the 120 mm width.

What do inner tube sizes mean?

An inner tube label states three things: a single rim diameter, a range of tire widths and a valve specification. A typical label reads 700 x 28–32C, Presta 48 mm or ETRTO 28/32-622, SV 48.

• Diameter (622 or 700 in this example) must match the tire's bead seat diameter.
• Width range (28–32 mm in this example) covers the tire widths the tube is designed to fill. Any tire from 28-622 to 32-622 is covered.
• Valve type and length, such as Presta 48 mm, tell you which rim hole the valve fits and how far the stem reaches.

Tubes are sold in ranges rather than single sizes because rubber stretches. One tube can fill several neighbouring tire widths. Ranges vary between brands, so read the exact numbers on the box rather than assuming that two tubes with similar names cover the same widths.

Bicycle inner tube size conversion chart

The bicycle tire tube size chart below matches common inch and French names to their ETRTO bead seat diameter. Tubes are interchangeable only between rows that share the same bead seat diameter.

Common name (inch or French)	Bead seat diameter (mm)	Typical use	Example ETRTO size
29 x 2.0–2.6 / 700C / 28 inch	622	Road, gravel, hybrid, 29er MTB, city	25-622, 40-622, 57-622
27 x 1 1/4	630	Older road bikes	32-630
28 x 1 1/2	635	Traditional roadster bikes	40-635
27.5 x 2.0–2.8 / 650B	584	Modern MTB, some gravel and touring	47-584, 57-584
26 x 1 3/8 (650A)	590	Older city and touring bikes	37-590
650C	571	Small road and triathlon bikes	23-571
26 x 1.5–2.5 (decimal)	559	Classic MTB, cruisers, some touring	54-559
24 x 1.5–2.4 (decimal)	507	Youth MTB	50-507
20 x 1.5–2.4 (decimal)	406	BMX, children's bikes, many folding bikes	47-406
20 x 1 1/8 or 1 3/8	451	Some folding, recumbent and junior road bikes	28-451
18 inch	355	Children's and folding bikes	47-355
16 x 1.75–2.125 (decimal)	305	Children's bikes	47-305
16 x 1 3/8	349	Some folding bikes	35-349
14 inch	254	Children's bikes	47-254
12 1/2 inch	203	Small children's bikes	57-203

Why the same inch size can need different tubes

One nominal inch size can correspond to several different rims, so the inch name alone is not enough to buy a tube. Tires called 26 inch exist with 559, 571, 584 and 590 mm bead seat diameters. Tires called 20 inch exist with 406 and 451 mm bead seat diameters. Tires called 28 inch exist with 622 and 635 mm bead seat diameters. Always confirm the ETRTO second number before buying a tube.

Road bike inner tube size chart

Almost all modern road bike tubes are 700C, or 622 mm bead seat diameter. The choice comes down to width range and valve length. The ranges below are typical examples. The exact limits vary by brand.

Tire size on sidewall	ETRTO tire size	Typical tube label	Typical valve
700x23C	23-622	700 x 18–25C	Presta
700x25C	25-622	700 x 18–25C or 700 x 25–32C	Presta
700x28C	28-622	700 x 25–32C	Presta
700x32C	32-622	700 x 25–32C or 700 x 32–47C	Presta or Schrader
700x38C to 700x45C	38-622 to 45-622	700 x 35–43C or 700 x 32–47C	Presta or Schrader
650x23C	23-571	650 x 18–25C	Presta

A 25 mm tire often appears at the edge of two ranges, such as 18–25 and 25–32. Either tube can work. The narrower-range tube is usually lighter. The wider-range tube is stretched less when inflated.

Inner tube width range: how much flexibility is there?

The tube's width range is the compatible tire width range recommended by the manufacturer. Staying inside it is the safe choice. The rim diameter has no equivalent flexibility.

• Diameter has no tolerance. A 584 mm tube in a 622 mm tire is too short, and the reverse leaves excess rubber that folds inside the tire.
• Too narrow a tube must stretch further to fill a wide tire. The rubber becomes thinner than designed.
• Too wide a tube has extra material that can bunch up. It is also harder to fit without trapping it under the tire bead, which can cause a blowout when inflated.

Riders sometimes use a tube slightly outside its printed range, but the result depends on the specific tube and tire. The manufacturer's range is the only figure you can rely on.

Valve type and valve length

The valve must fit the rim's valve hole. The valve stem must be long enough to stick out past the rim so a pump head can grip it. Valve compatibility is set by the rim, not the tire.

Valve type	Other names	Rim hole	Where it is common	Notes
Presta	SV, FV, French valve	About 6 mm	Road, gravel, most performance MTB	Thin stem with a locknut. Available in several stem lengths. Some have removable cores.
Schrader	AV, auto valve, American valve	About 8.5 mm	Children's, BMX, city, hybrid, many MTB	Same valve as car tires. Usually one standard length.
Dunlop	DV, Woods, EV	Schrader-size hole	City bikes in parts of Europe and Asia	Most modern versions inflate with a Presta pump head.

A Presta tube can go into a Schrader-size rim hole with an adapter grommet or by accepting some movement of the stem. A Schrader tube does not fit a Presta-size hole unless the rim is drilled out. That is not advisable on narrow rims, and drilling can affect rim strength and warranty.

How to choose valve stem length

Choose a valve stem length that equals your rim depth at the valve hole plus enough exposed stem for the pump head. A common rule of thumb is about 15–20 mm of exposed stem. Presta tubes are commonly sold in lengths of roughly 40, 48, 60 and 80 mm.

• Shallow rims of about 20–25 mm or less: a 40–48 mm valve is usually sufficient.
• A 40 mm deep rim: a 60 mm valve leaves about 20 mm exposed (60 − 40 = 20).
• Rims of about 50 mm or deeper: an 80 mm valve, or a removable-core Presta valve with an extender.

Brands do not always measure valve length the same way, so check how the stated length is defined if the margin is tight.

How tire width and rim diameter affect diameter and circumference

A bicycle tire's approximate overall diameter equals the bead seat diameter plus twice the tire height. Because bicycle tire height is roughly equal to width, a simple calculation is:

Overall diameter (mm) ≈ bead seat diameter + 2 x tire width
Circumference (mm) ≈ overall diameter x 3.1416

Tire size	ETRTO	Calculated diameter (mm)	Calculated circumference (mm)
700x25C	25-622	622 + 50 = 672	about 2111
700x32C	32-622	622 + 64 = 686	about 2155
700x38C	38-622	622 + 76 = 698	about 2193
27.5 x 2.25	57-584	584 + 114 = 698	about 2193
29 x 2.25	57-622	622 + 114 = 736	about 2312
26 x 2.10	54-559	559 + 108 = 667	about 2095
20 x 1.75	44-406	406 + 88 = 494	about 1552

These calculations show three practical points:

• Width changes size modestly. Going from 700x25C to 700x32C adds about 14 mm of diameter and about 44 mm of circumference. That is roughly a 2% change. Both tires still use a 622 mm tube, although possibly from different width ranges.
• Similar outer size does not mean the same tube. A 700x38C and a 27.5 x 2.25 tire have about the same calculated diameter of 698 mm. They sit on different rims, 622 mm and 584 mm, so their tubes are not interchangeable.
• Rim diameter dominates. A 29 x 2.25 and a 27.5 x 2.25 tire have the same width but different bead seat diameters. The difference is 38 mm in diameter and about 119 mm in circumference.

For motorcycle-style sizes with an aspect ratio, calculate sidewall height first. For a 120/70-12 tire, the height is 120 x 0.70 = 84 mm. The rim diameter is 12 x 25.4 = 304.8 mm. The calculated overall diameter is 304.8 + 2 x 84 = about 473 mm.

Calculated geometry versus actual tire dimensions

Calculated diameter and circumference are estimates for comparison, not exact measurements. Actual size differs for several reasons:

• Real tire width varies with rim inner width. A wider rim generally spreads the tire wider than its printed size.
• Tire height is not always equal to width.
• Inflation pressure, casing construction, tread depth and rider weight all change the measured diameter and the rolling circumference.

If you need an accurate circumference, for example for a bike computer, measure one full wheel revolution on the ground with the bike loaded.

These calculations also do not tell you whether a different tire will fit your frame or fork. Clearance is a separate question. For choosing a tube, only the bead seat diameter and the width range matter.

What does 36 mean in tube sizing?

The number 36 can refer to three different things on bike tires and tubes, so read it in context:

• Tire width of 36 mm. A 700x36C tire is 36-622, which falls inside common tube ranges such as 700 x 35–43C or 32–47 mm.
• 36-inch wheels. These are used on some unicycles and specialty bikes. They have a bead seat diameter of 787 mm and need tubes made specifically for that size.
• Valve length. Valve stem lengths are given in millimetres, but most Presta tubes come in about 40, 48, 60 or 80 mm. If you see a length figure on a box, confirm whether it refers to the valve or to the tire width.

Is there a standard bike inner tube size?

There is no single standard bike inner tube size. The right tube depends on your tire's bead seat diameter, width and valve. The most common sizes by bike type are:

• 700C (622 mm) in a 25–32 mm range for road bikes.
• 700C (622 mm) in a wider range of about 35–47 mm for gravel, hybrid and city bikes.
• 29 inch (622 mm), 27.5 inch (584 mm) or 26 inch (559 mm) for mountain bikes, in widths of roughly 2.0–2.6 inches.
• 20 inch (406 mm) for BMX and many children's and folding bikes.

The dependable method is the same for every bike. Read the ETRTO size on the tire, match the second number exactly, make sure the first number is inside the tube's width range, and select the valve type and stem length your rim requires.