Green’s Dictionary of Slang

1. (Aus.) a glass of beer.

1885

Bulletin (Sydney) 14 Mar. 12/1: Vain thought! we had not gone a perch, / A perch but only four, / When we beheld a feeble ghost / Outside of Alfred’s door.

2. (US campus) a pint of liquor.

1975

G. Underwood ‘Razorback Sl.’ in AS L:1/2 63: perch n Pint (of liquor).