Sources and scope for this page: ASME B29.1-2011 (R2016), covering the chain numbers, pitch, roller diameters and tensile strengths; and ISO 606:2015, covering the ISO chain numbering referenced in the comparison. No independent source check is recorded for this page: the content rests on the sources listed and on the working shown on the page. Full sources, values and limits on this page.
Page last changed 2026-10-19 · based on ASME B29.1-2011 (R2016)
ANSI Roller Chain Dimensions (ASME B29.1)
| Chain no.[1] | Pitch in[1] | Pitch mm[2] | Roller dia in[1] | Inner width in[1] | Tensile strength lbf[1] | Tensile strength kN[2] | Number ÷ 80 in[3] |
|---|---|---|---|---|---|---|---|
| 25 # | 0.250 | 6.350 | 0.130 | 0.125 | 780 | 3.5 | — |
| 35 # | 0.375 | 9.525 | 0.200 | 0.188 | 1760 | 7.8 | — |
| 40 # | 0.500 | 12.700 | 0.312 | 0.312 | 3130 | 13.9 | 0.5000 |
| 41 # | 0.500 | 12.700 | 0.306 | 0.250 | 2000 | 8.9 | 0.5125 |
| 50 # | 0.625 | 15.875 | 0.400 | 0.375 | 4880 | 21.7 | 0.6250 |
| 60 # | 0.750 | 19.050 | 0.469 | 0.500 | 7030 | 31.3 | 0.7500 |
| 80 # | 1.000 | 25.400 | 0.625 | 0.625 | 12500 | 55.6 | 1.0000 |
| 100 # | 1.250 | 31.750 | 0.750 | 0.750 | 19500 | 86.7 | 1.2500 |
| 120 # | 1.500 | 38.100 | 0.875 | 1.000 | 28000 | 124.6 | 1.5000 |
| 140 # | 1.750 | 44.450 | 1.000 | 1.000 | 38000 | 169.0 | 1.7500 |
| 160 # | 2.000 | 50.800 | 1.125 | 1.250 | 50000 | 222.4 | 2.0000 |
| 180 # | 2.250 | 57.150 | 1.406 | 1.406 | 63000 | 280.2 | 2.2500 |
| 200 # | 2.500 | 63.500 | 1.562 | 1.500 | 78000 | 347.0 | 2.5000 |
| 240 # | 3.000 | 76.200 | 1.875 | 1.875 | 113000 | 502.6 | 3.0000 |
Pitch comes from the chain number for sizes 40 and up. Divide the number by 80: chain 40 is 0.500 in, 60 is 0.750, 100 is 1.250, 240 is 3.000. The rule holds across the whole range above 40, and it is why chain numbers look arbitrary at first — they are pitch in eighths of an inch, eight times over.
Chains 25 and 35 are the exceptions and do not follow it: 25 has a 0.250 in pitch where the rule would give 0.3125, and 35 has 0.375 where it would give 0.4375. They are the small sizes, outside the original series.
Tensile strength is not the working load. The published figure is the load at which the chain breaks, and chain drives are normally selected at a working load around one-sixth to one-seventh of it, with the exact service factor depending on the shock characteristics of the drive. It also assumes the whole chain shares the load, which is not true for a chain on a sprocket with few teeth — that is why small sprockets carry a power rating penalty.
Chain Number, Pitch and Working Load
The chain number is a pitch designation rather than a strength rating, though the two track each other because a larger pitch means larger plates and pins.
Pitch sets the geometry. It determines the sprocket diameter for a given tooth count and therefore the drive's speed ratio and centre distance. It does not by itself determine how much power the chain carries.
Working load is a fraction of tensile strength, typically one-sixth to one-seventh, with the service factor reflecting shock. A drive with frequent starts, reversing loads or impact uses a larger factor and therefore a larger chain than a smooth drive of the same nominal power.
Sprocket tooth count matters as much as chain size. A chain wrapped around a small sprocket articulates through a larger angle at each tooth, which increases wear and concentrates load on fewer rollers. Manufacturers publish power ratings by chain size, sprocket tooth count and speed, and the tooth count penalty is substantial — the same chain carries appreciably less power on a 13-tooth sprocket than on a 25-tooth one.
Standard roller chain is also available in heavy series, where the plates are thicker for the same pitch and roller diameter. The two are identifiable by the same number but are not interchangeable on a sprocket, so the series should be confirmed before ordering.
Frequently Asked Questions
- How is roller chain size determined?
- By the ANSI chain number, which encodes the pitch. For chain 40 and above, pitch in inches is the number divided by 80 — chain 40 is 1/2 in, 80 is 1 in, 160 is 2 in. Chains 25 and 35 do not follow the rule.
- What is the breaking strength of 40 chain?
- 3,130 lbf (about 13.9 kN) for standard ANSI 40 roller chain. That is the tensile strength, not a working load — chain drives are normally selected at roughly one-sixth to one-seventh of that, with the factor depending on how much shock the drive sees.
- What is the difference between ANSI 40 and 41 chain?
- 41 has the same 1/2 in pitch but a narrower inner width (0.250 against 0.312 in) and lower tensile strength. It fits narrower sprockets and is used where space is tight, but it carries less load. The two are not interchangeable on the same sprocket.
- How do I calculate the length of roller chain I need?
- Count the teeth on both sprockets and the centre distance, then apply the standard chain length formula. The result must be rounded up to an even number of pitches because chain is supplied in even-pitch lengths and a connecting link joins the ends.
- Why does a small sprocket reduce chain capacity?
- Because the chain articulates through a larger angle at each tooth, and fewer rollers share the load. Both effects increase wear and reduce the power the chain can transmit. Manufacturer rating tables give lower capacities for small tooth counts, and 17 teeth is a common minimum for a drive sprocket.
Related
Value Sources
References and calculation methods used for this page are listed below. Numbered markers connect table columns where present. A reference listing does not itself establish that every value has been independently checked.
| # | Source | Type | Revision / method |
|---|---|---|---|
| [1] | ASME B29.1 — Precision Power Transmission Roller Chains, Attachments and Sprockets | reference | ASME B29.1-2011 (R2016) |
| [2] | Value computed from the standard's defining relationship | derived | Computed at build time from the defining formula and verified against every row. |
| [3] | Value computed from the standard's defining relationship | derived | Computed at build time from the defining formula and verified against every row. |
| [4] | ISO 606 — Short-pitch transmission precision roller and bush chains | reference | ISO 606:2015 |
Data Sources
| Standard | Revision | What it covers on this page |
|---|---|---|
| ASME B29.1 — Precision Power Transmission Roller Chains, Attachments and Sprockets | ASME B29.1-2011 (R2016) | the chain numbers, pitch, roller diameters and tensile strengths |
| ISO 606 — Short-pitch transmission precision roller and bush chains | ISO 606:2015 | the ISO chain numbering referenced in the comparison |
Verification scope
No page-specific independent source review is recorded here. The listed references and formulas explain the basis of the compilation; automated consistency checks do not verify the original sources or establish product conformity.
Derived values — the following values on this page are calculated, not taken directly from the standard:
| Value | How it is derived |
|---|---|
| Pitch in millimetres and tensile strength in kN | Inches × 25.4 and lbf × 4.44822 ÷ 1000, both exact, recomputed at build time. |
| Chain number ÷ 80 | The pitch rule for ANSI chain numbers of 40 and above. Shown alongside the actual pitch so the rule and its two exceptions are both visible. |
Pitch, roller diameter and width are standard dimensions. Tensile strength is the breaking load published by the manufacturer and varies between makers; the working load is a fraction of it set by the service factor. Power ratings by sprocket tooth count and speed come from the manufacturer's catalogue.
Cite This Page
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