I take a size forty-two.
'Quarantadue' — stress 'qua-RAN-ta-DUE'. The 'qu' is always 'kw' in Italian, never 'k' alone.
When asked your size, or when looking for something specific on a rail. Knowing your Italian size makes shopping much smoother.
'Porto' from 'portare' — in clothing context it means 'I wear/take'. The definite article 'la' precedes the size number in Italian, which is a unique structure.
Sono una taglia media.
I'm a medium.
Alternative using S/M/L sizing, increasingly common
Sono tra la M e la L.
I'm between M and L.
Useful when you're between sizes
Di solito prendo la S.
I usually take an S.
Casual way to express size
Italian tailoring heritage means sizing is taken seriously. In quality stores, staff may suggest measuring you properly rather than just trusting a number from another country.