Roller Chain Size Chart: ANSI and BS Sizes in mm and Inches

Choosing a roller chain starts with identifying its size and series. A chain that looks similar to an existing one may have a different roller diameter or inner width, which matters when checking it against the sprocket.

This guide explains the key measurements, compares selected ANSI and BS-series sizes, and shows a simple way to measure pitch. Use it to narrow down the dimensions you need before confirming the product specification for your replacement or new drive.

The Roller Chain Dimensions to Check

Start with these four details. They describe different parts of the chain, so one measurement cannot replace the others.

Figure 1. Roller Chain Dimensions: Pitch, Roller Diameter and Inner Width

For installation clearance, also check the overall width and connecting-link dimensions. The inner width describes the gap inside the chain; it does not tell you how much space the complete assembly needs.

ANSI and BS-Series Roller Chains: Which Family Do You Have?

Common ANSI designations include #40, #50 and #60. The American transmission-chain standard ASME B29.1 addresses chains and their associated sprockets. European-style chains are often listed as BS or B series, with codes such as 08B-1, 10B-1 and 12B-1. In those B-series examples, “-1” identifies a single-row chain.

ISO 606 is an international standard for short-pitch transmission roller and bush chains and their sprockets; it is not an exclusively European standard. Germany publishes an adoption as DIN ISO 606. For a practical comparison, keep the series designation alongside the measurements rather than identifying a chain only as “American,” “European” or “metric.”

Units and chain series are different things. A 12.7 mm pitch is the same distance as 0.500 inch. Expressing an ANSI chain in millimeters does not turn it into a B-series chain. The two tables below are separate references, not a list of interchangeable pairs.

Roller Chain Size Charts

The following tables cover selected single-row chains. Each dimension has its own adjacent mm and inch columns. These values are dimensional references only, rather than an inventory list or a substitute for the product's official drawings and application ratings.

Selected ANSI Roller Chain Sizes

Reference: [4], printed pp. 10–16. Inch values retain the source catalog's precision; mm values are calculated using 1 inch = 25.4 mm and rounded to three decimal places. These converted figures are not additional manufacturing tolerances.

Selected BS / B-Series Roller Chain Sizes

Reference: [5], printed p. 4. “Max.” and “min.” preserve the source table's dimensional limits. The inch equivalents for diameter and width are rounded reference conversions, not inspection limits; use the original mm values and applicable product specification for engineering checks.

Are #40 and #41 the Same Size?

No. #40 and #41 are different chain sizes. Both have a 12.7 mm pitch, but #41 is narrower between its inner plates and has a smaller roller diameter in the reference table. The equal spacing between pins does not make the complete chains identical. Do not choose one as a direct replacement for the other solely because their pitches match.

The same principle applies across series: #40 and 08B-1 both have a 12.7 mm pitch, but their roller diameters and inner widths differ. Confirm the full chain designation and the sprocket specification rather than treating the two tables as a conversion between products.

How to Measure Roller Chain Pitch in Millimeters

Use an accessible, straight section of chain. For an installed chain, stop and isolate the equipment under its approved procedure before measuring. Never measure a moving chain.

1. Find the Pin Centers

   Identify consecutive centers along the chain.

2. Straighten the Section Gently

   Take up slack without forcing a damaged or stiff joint.

3. Measure Across Several Intervals

   Record the center-to-center distance between your chosen endpoints in mm.

4. Count the Spaces, Not the Pins

   Six consecutive centers have five spaces between them.

5. Calculate and Cross-Check

   Divide the span by the number of spaces, then measure roller diameter, inner width and row count to narrow down the size.

Figure 2. Measuring Roller Chain Pitch: Six Pin Centers, Five Intervals

Allow for wear when identifying an old chain. Wear at the pin-and-bushing joints can increase the measured span. Compare the reading with the chain markings and equipment specification; a slightly longer reading does not automatically indicate a different nominal size. Formal wear inspection should follow the relevant measuring conditions and service limits.

What to Confirm Before Ordering

Once you have a likely size, bring these details together:

1. Chain designation and series: Include the full code and any special suffixes, not only the pitch.
2. Dimensions and row count: Check pitch, roller diameter, inner width, overall clearance and connecting-link type.
3. Sprocket specification: Confirm the chain series and row arrangement the sprocket is designed for.
4. Required length: Specify the chain length or number of pitches using the supplier's ordering convention.
5. Operating requirements: Confirm the selected product's ratings for the drive's load, speed, lubrication and environment. A dimensional match is one part of selection, not a load rating.

FAQ about Roller Chain Sizing

Conclusion: Roller Chain Size Selection

Start with the chain series, then compare pitch, roller diameter, inner width and row count in millimeters. Measure across correctly counted intervals and use the full designation when checking a product or sprocket. This gives you a clearer basis for choosing a chain for replacement or a new drive.

With those details ready, explore JLCMC's sprockets and chains and check the specifications of the product you are considering.