What size is my roller chain?

Measure pitch, roller diameter, and inside width and match them to the chart. Pitch in eighths of an inch gives the family, so 0.500 in pitch is #40 or #41, and the width decides which.

What does #40 chain mean?

The 4 means a pitch of 4/8 in, or 0.500 in, and the 0 means standard roller chain. #40 has 0.312 in rollers and a 0.312 in inside width.

What is the difference between #40 and #41 chain?

Both have a 0.500 in pitch, but #41 is a lightweight chain with a narrower 0.250 in inside width and 0.306 in rollers. They need different sprockets: 0.284 in tooth width for #40 and 0.227 in for #41.

Is #40 chain the same as 08B?

No. Both are 12.7 mm pitch, but 08B has 8.51 mm rollers and a 7.75 mm inside width versus 7.92 mm and 7.94 mm for #40. ANSI #40 matches ISO 08A.

How do I measure chain pitch accurately?

Measure across several pitches and divide, because a single pitch is hard to read. Ten pitches of #40 chain measure 5.00 in when new.

When should a roller chain be replaced?

Replace it at about 3% elongation, a common industrial limit. For #40, that means 10 pitches measuring about 5.15 in instead of 5.00 in.

What sprocket tooth width does each chain need?

For single-strand sprockets, tooth width is about 0.93 × inside width − 0.006 in. That gives 0.284 in for #40, 0.343 in for #50, and 0.459 in for #60.

Power transmission calculator

Roller Chain Size Chart (ANSI #25 to #120)

ANSI roller chain size chart with pitch, roller diameter, inside width, pin diameter, and sprocket tooth width, plus how to identify your chain.

Calculator inputs

Results update as you type. Switch units at any time without changing the physical values.

Set all

Results

Chain links (even): 76
Exact length in pitches: 75.34
Chain length: 38 in
Center distance: 12.1657 in
Center distance in pitches: 24.33
Speed ratio (driven ÷ driver): 2
Wrap on small sprocket: 166.5 °

Chain drive layout

Both sprockets and the chain drawn to scale at the calculated center distance, with every link in place.

Generate these sprockets

Driver pitch diameter: 2.879 in
Driven pitch diameter: 5.737 in
Center distance: 12.166 in

The center distance is 24.3 pitches. About 30 to 50 pitches is ideal for chain life; up to 80 works with a guide or idler.

Make these sprockets

Generate laser-cut plate sprockets for this drive with ASME B29.1 teeth, one at a time or as a matched set.

More sprocket options

Bore and holes

Bore

Bore diameter

Mounting holes

Lightening holes

Fabworks plate material

Plate thickness for chain fitMin. feature 0.050 in · 1.27 mm

Download the manufacturing files

100% in-browser

STEP solids are built and checked in your browser. DXF and SVG drawings use lines and true arcs at full scale. Nothing is uploaded until you order.

Driver sprocket
3.136 in × 3.096 in
Driven sprocket
⌀ 5.995 in

Laser cut it at Fabworks

We generate the STEP files, add them to a new quote, and open it in a new tab where you can review material, finish, and quantity.

Ready to make the part?

Turn the mechanism into real parts. Upload your plate, sheet, or tube CAD for an instant Fabworks quote.

Quick answer

How this roller chain size chart calculator works

ANSI roller chain numbers give the pitch in eighths of an inch: #40 is 4/8 = 0.500 in, #60 is 0.750 in, and #80 is 1.000 in. A last digit of 0 means standard roller chain, 1 means lightweight (#41), and 5 means rollerless bushing chain (#25, #35). The chart lists pitch, roller diameter, inside width, pin diameter, and matching sprocket tooth width for #25 through #120.

How to use the calculator

1Measure pitch from the center of one pin to the center of the next, or across several pins and divide.
2Measure the roller diameter and the inside width between the inner link plates.
3Match all three values to a row in the chart; pitch alone does not separate #40 from #41 or ISO 08B.
4Use the calculator to get chain length or center distance for that size.

Step by step

How to identify roller chain size

1Clean the chain and look for a size stamped on the side plates, such as 40 or 08B.
2Lay the chain flat and measure across 10 pitches, pin center to pin center, then divide by 10.
3Convert to eighths of an inch: 0.500 in is 4/8, so the chain is in the #40 family.
4Measure roller diameter with calipers.
5Measure inside width between the inner plates to separate #40 (0.312 in) from #41 (0.250 in).
6Compare all three values with the chart; if they read metric, check the ISO B-series sizes.
7Check wear: replace the chain when it has stretched about 3% over a measured length.

Worked example

Identifying an unmarked chain

Inputs: Ten pitches measure 5.00 in, the rollers are 0.312 in, and the inside width is 0.312 in.
Result: Pitch 0.500 in with 5/16 in rollers and width: ANSI #40.

A #41 chain has the same 0.500 in pitch but 0.306 in rollers and a 0.250 in inside width, and ISO 08B has 8.51 mm (0.335 in) rollers.

Common questions

What to know before using the result

What size is my roller chain?: Measure pitch, roller diameter, and inside width and match them to the chart. Pitch in eighths of an inch gives the family, so 0.500 in pitch is #40 or #41, and the width decides which.
What does #40 chain mean?: The 4 means a pitch of 4/8 in, or 0.500 in, and the 0 means standard roller chain. #40 has 0.312 in rollers and a 0.312 in inside width.
What is the difference between #40 and #41 chain?: Both have a 0.500 in pitch, but #41 is a lightweight chain with a narrower 0.250 in inside width and 0.306 in rollers. They need different sprockets: 0.284 in tooth width for #40 and 0.227 in for #41.
Is #40 chain the same as 08B?: No. Both are 12.7 mm pitch, but 08B has 8.51 mm rollers and a 7.75 mm inside width versus 7.92 mm and 7.94 mm for #40. ANSI #40 matches ISO 08A.
How do I measure chain pitch accurately?: Measure across several pitches and divide, because a single pitch is hard to read. Ten pitches of #40 chain measure 5.00 in when new.
When should a roller chain be replaced?: Replace it at about 3% elongation, a common industrial limit. For #40, that means 10 pitches measuring about 5.15 in instead of 5.00 in.
What sprocket tooth width does each chain need?: For single-strand sprockets, tooth width is about 0.93 × inside width − 0.006 in. That gives 0.284 in for #40, 0.343 in for #50, and 0.459 in for #60.

Reference

ANSI roller chain size chart (in)

Nominal ASME B29.1 dimensions. #25 and #35 are rollerless, so the diameter shown is the bushing. Tooth width is for single-strand sprockets.

Chain	Pitch	Roller dia	Inside width	Pin dia	Sprocket tooth width
#25	0.250	0.130	0.125	0.091	0.110
#35	0.375	0.200	0.188	0.141	0.168
#40	0.500	0.312	0.312	0.156	0.284
#41	0.500	0.306	0.250	0.141	0.227
#50	0.625	0.400	0.375	0.200	0.343
#60	0.750	0.469	0.500	0.234	0.459
#80	1.000	0.625	0.625	0.312	0.575
#100	1.250	0.750	0.750	0.375	0.692
#120	1.500	0.875	1.000	0.437	0.924

ANSI chain in millimeters with ISO 606 designations

ISO A-series chain is dimensionally the ANSI chain. B-series (British standard) chain with the same pitch has different rollers and widths and needs its own sprockets.

ANSI	ISO 606	Pitch (mm)	Roller dia (mm)	Inside width (mm)	Same-pitch B-series
#25	04C	6.35	3.30	3.18	none
#35	06C	9.525	5.08	4.76	06B
#40	08A	12.70	7.92	7.94	08B
#41	085	12.70	7.77	6.35	none
#50	10A	15.875	10.16	9.53	10B
#60	12A	19.05	11.91	12.70	12B
#80	16A	25.40	15.88	15.88	16B
#100	20A	31.75	19.05	19.05	20B
#120	24A	38.10	22.23	25.40	24B

Formula

L = 2C/p + (N₁ + N₂)/2 + p·(N₂ − N₁)² ÷ (4π²·C)

Chain length L in pitches comes from center distance C, chain pitch p, and the small and large sprocket tooth counts N₁ and N₂, rounded up to an even link count. Center distance for a given link count is C = (p/4)·[A + √(A² − 2(N₂ − N₁)²/π²)], where A = L − (N₁ + N₂)/2.

Engineering references

Assumptions and limits

Presets use nominal ANSI roller chain pitch values covered by ASME B29.1.
Lengths and center distances are for a taut two-sprocket drive with no slack or idlers.
Odd link counts need an offset link, which is weaker than standard links.
Wrap angle uses pitch diameters and is checked against a 120° minimum on the small sprocket.
Chain wear and tensioning allowance are not included; provide center-distance adjustment.

Educational estimate

Use this result for learning and early design exploration. Verify safety-critical or production decisions with the governing standard, material data, real tooling, and a qualified engineer.

Keep designing

Fabworks resources

Related calculators

Order Sheet Metal Parts

Upload a 2D DXF or 3D STEP file for an instant laser cutting quote. Quote in seconds, order in minutes, receive parts in days.

Browse Files

or drag and drop

STEP / DXF up to 24MB

Your files are safe, secure, and retain all intellectual rights.