A Certain Ratio (abbreviated as ACR) are an English post-punk band formed in Greater Manchester in 1977 by Peter Terrell (guitar), Simon Topping (vocals, trumpet), Jez Kerr (bass guitar, vocals), Martin Moscrop (trumpet, guitar) and Donald Johnson (drums), with Martha Tilson (vocals) joining soon after.

One of the first white indie groups to draw heavy influence from funk as well as disco and Latin percussion, the band were among the first to debut on Tony Wilson's Factory Records in 1979 with "All Night Party," produced by Martin Hannett. During ACR's early years with Factory, they scored seven Top Ten UK independent releases, highlighted by "Flight" and "Waterline," and released five studio albums beginning with The Graveyard and the Ballroom (1980).

Following late 1980s and early 1990s phases with A&M Records and Rob Gretton's independent Robs Records, ACR were intermittently active. They returned to the studio for their ninth studio album Mind Made Up (2008) and since then have continued to perform, with their back catalogue recirculated through an arrangement with Mute Records.

They released their first new studio album in twelve years, ACR Loco in September 2020, followed by three EP's A, C and R in 2021, and eleventh studio album, 1982, in 2023. Their twelfth studio album, It All Comes Down to This will be released in 2024.