"customisation" vs "customization" Which is correct? [duplicate]

The "z" is American, the "s" is British. As an American I always use "z" for these words, and apparently many UK spellcheckers do not mark it as wrong and the Oxford English dictionary even gives "organization" as the first spelling, saying (also organisation).

Yet my (US English) Firefox marks the "organisation" variant as misspelled and suggests "organization".

My advice: unless you are writing under guidelines that suggest otherwise, use the "z" form for these words.

You often hear people say that -ize is American and -ise is British. While it is certainly true that -ise has become dominant in Britain, -ize is the older spelling, and it once was dominant everywhere. Americans have retained it, while the British have increasingly – since the mid-20th-century I think – favoured -ise. Why, I don't know.

Last time I checked, both the (British) Oxford and Collins dictionaries gave -ize as the first spelling.

I'm British and I always use the -ize spelling, not least because the letter z is so underused, but also because it more accurately indicates its pronunciation (and -ise is plain ugly).

In publishing, we usually call these -ize and -ise spellings. Some UK publishers prefer -ize, but -ise is the predominant UK style.

See Oxford spelling on Wikipedia. OED prefers -ize spellings.

The US requires -ize. The UK accepts both, but (with the OUP as the main exception) prefers -ise. And this is one of the few cases where "international" English follows the US convention. The ISO favours -ize spellings.

Inbuilt computer dictionaries set to UK English rarely support -ize. Feel free to overrule them.