V-belt sizes chart: A, B, C, Z (M) and SPZ widths, and how to read the number

V-belt sizes are a section letter plus a length: the letter sets the top width (Z or M 10 mm, A 13 mm, B 17 mm, C 22 mm, SPZ 10 mm) and the number the length. On A, B and C belts it's the inside length in inches, so our A93 V-belt is 93 inches inside.

If you can read the code on your old belt, order the same code and you can stop here. If not, the table gives each section's size and what its number measures.

Source: belt makers' published section tables (see Sources); size ranges from our product listings. Read 30 September 2026. These widths are nominal. Our B listings give B as 5/8" (17 mm), our M listing gives M as 3/8" (9.5 mm), and our SPZ listing gives SPZ as 9.5 to 10 mm.

How to read a V-belt number: inside, outside or datum

The letters are the section and the number is a length, but the length is measured in a different place on different belts.

• Z (M), A, B and C (classical belts): the number is the inside length in inches, so an A30 is 30 inches inside. The outside is longer by 1 inch on Z, 2 on A, 3 on B and 4 on C, so an A belt that measures 32 inches outside is an A30. On C belts above about C210, the difference is 2 inches, not 4.
• Datum length: belt makers' tables also give a datum length in millimetres for every classical belt. On A, B and C belts it sits between the inside and outside lengths; on Z belts the datum is within a few millimetres of the outside. An A93 is 2400 mm datum and 2415 mm outside, while 93 inches inside is about 2362 mm. If a listing gives a datum length, don't take the full 2, 3 or 4 inches off it.
• SPZ and XPZ (narrow belts): the number is the datum length in millimetres, so an SPZ1000 is 1000 mm datum. There's no inch offset to add. Belt makers' catalogues say to measure the outside length in millimetres and find the closest datum length in the size list, but in our experience the number on the old belt is the safer guide, because a measurement can fall between two close SPZ sizes.
• US 4L and 5L belts: the number is the outside length in tenths of an inch, so a 4L450 is 45.0 inches outside. A 4L is the same 13 mm width as an A and a 5L the same 17 mm as a B, so a US listing needs converting before you order. See how to turn a "1/2 x 95" listing into an A size.
• Extra letters: an X means cogged (a BX77 is a cogged B77, same size and pulleys), explained in AX vs A, BX vs B, XPZ vs SPZ. On our belts a K means Kevlar, and suppliers write it either way round: AK93 and A93K are the same belt.

A 6PK belt (6PK2200, 6PK1230 and so on) isn't a V-belt at all: it's a ribbed (poly-V) belt, and the 6 is the number of ribs and the last figure the effective length, so we sell those separately in our 6PK belt range.

Z and M section belts: buy by the inside length

Z and M are two names for the same 10 mm section. Belt makers' tables list it as Z (M), and our listing sells M19 to M50 as Z19 to Z50 too.

The trap is the number stamped on the belt. Makers don't all measure M belts the same way. Our PIX belts are stamped with the inside length and our Allwyn belts with the outside, so the stamped numbers on two same-size belts can be an inch apart. Even a single belt maker's catalogue shows the muddle: its Z19, 510 mm outside, is listed as an M19, while its lighter 3L belt at 508 mm outside is cross-referenced to an M18.5.

So for an M or Z belt, go by the inside length, not the stamp. Measure round the outside of the old belt and take off 1 inch. Our M listings are numbered by inside length.

V-belt size chart: common sizes in inches and mm

Source: inside and outside inches for the M, A and B rows from our product listings; C outside inches from the C-section rule above (+4", or +2" above about C210; our C listings give the inside length only); datum and outside millimetres from belt makers' published section tables (see Sources). Read 30 September 2026. The SPZ tables give no outside length.

How to measure a V-belt and find its size

1. Read the old belt or the manual. We'd go by the maker's belt number before a tape measure. Check for an X (cogged) or K (Kevlar) in the code.
2. No code? Measure the top width with a steel rule: 10 mm, 13 mm (A), 17 mm (B) or 22 mm (C).
3. At 10 mm, check the depth. About 6 mm deep is a Z (M). About 8 mm deep is an SPZ.
4. Measure the outside length with a tape round the back of the belt.
5. Convert it. Take off 1 inch for Z (M), 2 for A, 3 for B or 4 for C to get the number. For SPZ, go by the number on the old belt. A tape measurement can land between two close sizes (we list both SPZ1000 and SPZ1010), so if the code has worn off, message us with the measurement before you order.
6. Between two sizes? Aftermarket belts come in 1 inch steps, and our longer ranges skip some sizes. If the machine has little adjustment left at the tight end, choose the larger belt. If it has little left at the loose end, choose the smaller one.
7. Match the build. If the old belt was Kevlar, buy Kevlar. See Do I need a Kevlar mower belt?

Which Bearings Express V-belt fits

• Pick the M-section V-belt range, M19 to M50 (Z19 to Z50) for an old belt that measures about 10 mm across the top and 6 mm deep (the nominal Z (M) section). Order it by the inside length.
• Pick the A-section V-belt range, A20 to A79 for a 13 mm belt up to 79 inches inside.
• Pick the A-section V-belt range, A80 to A154 for a longer A belt. It lists 48 sizes, so check yours is on the list. A158 is listed on its own in the A-section collection.
• Pick the B-section V-belt range, B24 to B88 for a 17 mm belt up to 88 inches inside. Longer B belts, up to B195, are in the B-section collection.
• Pick the C-section V-belt range, C38 to C80 for a 22 mm belt up to 80 inches inside. C81 to C376 are in the C-section collection.
• Pick the SPZ V-belt range, SPZ630 to SPZ3550 for an old belt that measures about 10 mm across the top and 8 mm deep (the nominal SPZ section) with an SPZ number.

Every A-section size we list is in the A-section V-belt collection.

Questions people also ask

What are the dimensions of a B section V-belt?

A B-section belt is 17 mm wide and 11 mm deep. The number is the inside length in inches and the outside is 3 inches longer, so a B77 is 80 inches outside. Our B listings give it as 5/8" (17 mm).

What size is an A section V-belt?

13 mm (1/2") wide and 8 mm deep. The number is the inside length in inches, and the outside is 2 inches longer, so an A93 is 95 inches outside.

Is a Z section belt the same as an M section belt?

Yes in the classical (wrapped) section tables: Z (M) is 10 mm wide and 6 mm deep. At least one belt maker also tags its lighter 3L belt (10 x 5 mm) as M, and we list M19 to M50 as Z19 to Z50. But makers stamp M belts with different lengths, so buy by the inside length: the outside less 1 inch.

What is a C section V-belt?

The widest classical section we sell: 22 mm (7/8") wide and 14 mm deep. The number is the inside length in inches. The outside is 4 inches longer, or 2 inches on belts above about C210.

Are V-belts measured inside or outside?

It depends on the section. Z (M), A, B and C numbers are inside lengths in inches, SPZ numbers are datum lengths in millimetres, and US 4L and 5L numbers are outside lengths in tenths of an inch.

Related reading

• Mower belt listed as "1/2 x 95"? How to turn it into an A or AK belt size
• AX vs A, BX vs B, XPZ vs SPZ: what the X means on a V-belt
• Do I need a Kevlar mower belt?

Sources

• Gates Australia, Industrial Power Transmission South Pacific Catalogue (2018): Hi-Power II sections p. 29, Z table p. 30, A table p. 31, B table pp. 32 to 33, C table pp. 35 to 36; Super HC sections p. 51 and SPZ table p. 52; Quad-Power 4 sections p. 61; Micro-V ordering code p. 69; Truflex sections p. 97 and 3L table p. 98; V-belt lengths and selection p. 173. Read 30 September 2026.
• Gates, Belt I.D. Chart (12998-J). Read 30 September 2026.
• Gates Australia, Heavy-duty product range: FleetRunner Micro-V belts (application data sheet). Read 30 September 2026.

Checked against the belt makers' catalogues above and Bearings Express product data on 30 September 2026.