Chain pitch is the basic dimension a roller chain repeats and the unit its length is counted in. For ANSI chain it never needs looking up, because ASME B29.1 makes it definitional in the chain number itself: pitch = (chain number ÷ 10) × 1/8 inch. A #40 chain has a 4/8 = 1/2 in pitch, #25 is 1/4 in, #60 is 3/4 in, #80 is 1 in, and #100 is 10/8 = 1-1/4 in. The trailing digit flags construction — 0 for standard roller chain, 5 (as in #25 and #35) for rollerless bushing chain.
Pitch threads through every drive-layout calculation. Chain length is computed in pitches — L = 2C/P + (N+n)/2 + (N−n)²/(4π²·C/P) — then multiplied by the pitch for inches and rounded up to an even link count, because chain closes on alternating inner and outer link plates and an odd count forces a weaker offset link. Sprocket pitch diameter is PD = P/sin(180°/N), locating the theoretical chain line, and chain velocity is P × n × rpm ÷ 12 in ft/min — the number lubrication regimes and horsepower tables key on.