guyfrommars says on 10/Sep/11
In The Ladykillers, he looked the same height as Peter Sellers (listed as 5'8.5" on this site), and both wore thick-heeled footwear. Although Guinness was slouching a bit, and Sellers' big hair made him look somewhat taller. In The Lavender Hill Mob, he looked around the same height as 5'9" Sid James. And James had footwear advantage (wearing boots with heels, clearly visible in one shot). I guess Guinnes was close to 5'9.5" in his younger days, but definately not under 5'9".

Sam says on 14/Jul/11
He doesn't look 5'7" usually, at least not until old age, though 5'9" might have been his absolute peak. Might you downgrade him a tad, Rob? You don't seem convinced of 5'9.5" in your comments above.

Bon_ says on 16/Apr/11
5'4 absolute max