I take a forty-two.
'Quarantadue' — qua-ran-ta-DU-e. Five syllables — roll through them.
State your size clearly when asked. Italian sizes are numbers, so knowing yours is essential. Learn both the Italian number word and the numeric digit for speed.
'Porto' (I take/wear) uses 'portare' with the clothing size. The definite article 'la' precedes the size number — 'la quarantadue'. This article agrees with 'la taglia' (feminine). You can also say just the number: 'Quarantadue' and the assistant will understand.
Porto una quarantadue.
I wear a forty-two.
Indefinite article — equally natural.
Sono una taglia M.
I am a size M.
International letter sizing — understood everywhere.
Di solito porto la M o la L, dipende dalla marca.
Usually I take M or L, it depends on the brand.
Honest answer — size varies by brand.
Italian clothing brands can size quite small compared to northern European or American brands. It is normal to take a size up — if your usual size feels tight, ask for 'una taglia più grande' (one size up).