Before you go, buy 1 Standard Hut Ticket (blue for adults, yellow for youth) for each night's stay. Put this in the honesty box at the hut. Or buy a Backcountry Hut Pass that gives unlimited use at most Standard and Serviced huts for a 6 or 12 month period.
Cullers Hut is 6 - 7 hours (19.5 km) up the Hopkins valley from Ram Hill carpark, at the end of Lake Ohau Road.
NZTopo50 map sheet: BY14
Grid/NZTM2000 coordinates: E1346027, N5131903