happy as the day is long/as a clam/as Larry

*happy as a clam (at high tide)

 and *happy as a clam (in butter sauce); *happy as a lark; *happy as can be
contented; very happy. (*Also: as ~.) I've been as happy as a clam since I moved to the country. I don't need much. Just somewhere to live, some work to do, and a TV to watch, and I'm happy as a clam at high tide. Matthew was happy as a lark throughout his whole vacation. Bob was happy as can be when he won the lottery.
See also: clam, happy

happy as the day is long

Also, happy as a lark; happy as a clam (at high tide). Extremely glad, delighted, very cheerful, as in He was happy as the day is long, or When she heard the news she was happy as a lark, or Once I got the test results I was happy as a clam at high tide. The first of these similes dates from the late 1700s. The second alludes to the lark's beautiful, seemingly very happy, song. The third, from the early 1800s, alludes to the fact that clams can only be dug at low tide and therefore are safe at high tide; it is often shortened to happy as a clam.
See also: happy, long

happy as a clam

AMERICAN
If you are happy as a clam, you are very happy. Join the other kids. Do that, and before you know it you'll be happy as a clam.
See also: clam, happy

happy as Larry

BRITISH, INFORMAL
If you are as happy as Larry, you are very happy. I gave her a police badge to wear on her sleeve and she was as happy as Larry. Note: `Larry' may refer to the successful Australian boxer Larry Foley (1847-1917). Alternatively, `Larry' may come from `larrikin', a 19th century word for a hooligan or ruffian, used mainly in Australia.
See also: happy, Larry

(as) happy as the day is ˈlong/as a ˈclam/as ˈLarry

(informal) very happy: Grandpa’s as happy as a clam helping the children to fly their kites.
See also: clam, happy, Larry, long