Green’s Dictionary of Slang

at the most, at the top estimate, e.g. five years tops, ten quid tops.

1928		J. O’Connor Broadway Racketeers 186: The toughest rap ever registered brought, at tops, a six month’s bit.
1938		D. Runyon ‘Pick the Winner’ in Runyon on Broadway (1954) 322: The professor does not seem anxious to bet a sawbuck, tops.
1953		R. Chandler Long Good-Bye 64: ‘How much do you make in a month, Marlowe ?’ [...] ‘Seven-fifty would be tops,’ he said.
1961		Mad mag. Oct. 9: They gave me this big shiny trophy. Big deal. $3.98 at Woolworth’s, tops.
1973		D. Ponicsan Cinderella Liberty 62: We could get a place, the five of us [...] for sixty dollars tops.
1986		C. Hiaasen Tourist Season (1987) 59: Her husband [...] was only about five-two, a hundred-ten pounds, tops.
1990		R.G. Barratt ‘Keystone Cops’ in What Do You Reckon (1997) [ebook] I’d be finished by midnight, tops.
1991		B. Hamper Rivethead (1992) 114: ‘How long do you think it’d take before some drunked-up redneck mauled one of the Bunnies to shreds?’ ‘Oh, probably fifteen seconds, tops.’.
2005		J. Stahl I, Fatty 158: I must have talked to her for 20 minutes tops.
2010		(con. 1973) C. Stella Johnny Porno 176: ‘At least [...] get an idea of the market value.’ ‘I already know that. One-twenty, tops’.
2020		(con. 1991-94) W. Boyle City of Margins 14: ‘She’s fifteen, tops’.
2021		C. Hammer Opal Country 196: ‘[T]en minutes tops’.