Up to eleven

[1] The phrase was coined in a scene from the 1984 rock mockumentary This Is Spinal Tap by the character Nigel Tufnel, played by Christopher Guest.

During a trial run with a reporter from Popular Mechanics aboard, a C&O engineer expressed his dissatisfaction with a local speed limit of 75 miles per hour (121 km/h), noting that he would "Sure like to be able to pull it back to eleven!

[6] As a consequence of the film, real bands and musicians started buying equipment whose knobs went up to 11, or even higher, with Eddie Van Halen reputedly being the first to do so.

[12][13] The "Drive" knob of the Elektron Syntakt drum computer and synthesizer goes from 0 to 11 with 1 in the middle, using 0—1 for normal clean audio levels followed by 10 additional steps of distorted range.

[14] On its primary page for This Is Spinal Tap, the IMDb site used to display the user rating for the film out of 11 stars (e.g. 7.9/11) instead of the standard scale of one to ten.