Calza vs. calzino
While both calza and calzino refer to garments worn on the feet, they are not interchangeable in Italian. The primary difference between them is length and context, with calzino being a diminutive of calza, implying something smaller.
Calza
B1Calza is a feminine noun that refers to a long sock, a stocking, or hosiery. It is used for socks that typically go up to the knee or higher, and it is also the specific word for a Christmas stocking.
Per la cerimonia ha indossato un elegante paio di calze di seta.
(For the ceremony, she wore an elegant pair of silk stockings.)
I bambini aspettano i dolci nella calza della Befana.
(The children wait for sweets in the Befana's stocking (a Christmas stocking).)
Il medico mi ha consigliato di usare calze a compressione per la circolazione.
(The doctor advised me to use compression stockings for circulation.)
Con questo freddo, metto sempre le calze di lana pesante.
(In this cold weather, I always wear heavy wool knee-high socks.)
Si è strappata una calza e ha dovuto cambiarla.
(She snagged a stocking and had to change it.)
Calzino
A1Calzino is a masculine noun and is the standard, everyday word for a short sock. It refers to the common socks that cover the foot and end at the ankle or mid-calf.
Ho perso un calzino in lavatrice, come sempre.
(I lost a sock in the washing machine, as always.)
Per favore, metti i calzini sporchi nel cesto della biancheria.
(Please, put your dirty socks in the laundry basket.)
Con le scarpe da ginnastica indosso sempre un calzino di cotone.
(With sneakers, I always wear a cotton sock.)
Mio nonno porta i sandali con i calzini bianchi.
(My grandfather wears sandals with white socks.)
Mi serve un paio di calzini nuovi per il lavoro.
(I need a new pair of socks for work.)
Summary
In essence, use calzino (plural calzini) for a standard, short sock that you would wear daily with sneakers or regular shoes. Use calza (plural calze) for a long sock (knee-high or thigh-high), a woman's stocking or tights, or for the traditional Christmas stocking. Think of calzino as the small, everyday sock and calza as its longer, more formal, or specialized counterpart.