Chain & Sprocket Length and Ratio Calculator

Direct answer. Enter chain pitch, sprocket tooth counts and an approximate center distance. The result gives a practical even-pitch chain length, the center distance for that length and the ideal speed ratio.

Method. In pitch units x = C/p, chain length is L = 2x + (N+n)/2 + (N-n)^2/(4 pi^2 x). The selected pitch count is rounded upward to the next even count, then the same relationship is solved algebraically for the adjusted center. Pitch diameter is p/sin(pi/z).

Worked example. Two 20-tooth sprockets at a nominal 500 mm center with 12.7 mm pitch require 98.74 pitches theoretically. Selecting 100 pitches gives a 1,270 mm chain and a 508 mm adjusted center.

The result above uses these exact values. This snapshot is included when the page is printed so the output can be checked against the original measurements.

Input units

Millimetres

Chain pitch

12.7

Driver sprocket teeth

20

Driven sprocket teeth

40

Approximate shaft center distance

500

Driver speed (RPM)

1200

Primary result: Selected chain: 110 pitches.

• Measure from the datum or reference edge described by this tool, and do not mix inside, outside and centerline dimensions.
• Keep inputs in the displayed units and preserve more precision than the final cutting or purchasing tolerance requires.
• When the result is close to a limit, verify it with a test piece, field measurement, manufacturer drawing or qualified project professional.

This is nominal two-sprocket roller-chain geometry. It does not rate chain size, power, speed, lubrication, alignment, wear, shock loading, tensioners or installation clearance. Avoiding an odd pitch count removes the need for an offset link, but does not replace the chain manufacturer's selection and installation rules.