On cloud nine Informal

Extremely happy, elated, or euphoric, often following good news or a wonderful experience.

It describes a temporary, intense state of joy rather than a lasting mood, and is almost always used positively.

The frequently repeated explanation — that the U.S. Weather Bureau once classified clouds by height and type, with “cloud nine” designating the tallest, most majestic cumulonimbus clouds reaching around 10,000 meters — is widely circulated but poorly substantiated; no properly documented weather-classification chart matching this specific story has been reliably traced by phrase researchers, and the tidy technical explanation has the hallmarks of an invented, after-the-fact rationalization rather than a genuine source. What can be verified is that American slang in the 1950s used a range of numbers for similarly euphoric cloud imagery, including “cloud seven” and “cloud eight,” before “cloud nine” eventually became the fixed, standard form; this instability in the exact number strongly suggests the choice of “nine” was arbitrary or simply became the one that stuck through popular use, rather than being tied to any specific meteorological classification. The broader idea of clouds symbolizing elevated happiness, of course, is much older and related to expressions like “walking on air” and “in seventh heaven.”

She’s been on cloud nine ever since she got the acceptance letter.

He was on cloud nine after his team won the championship.

Ever since the proposal, they’ve both been on cloud nine.

A: You look so happy today. B: I am — I’m on cloud nine after getting the job offer.