cheatsheet
Counters
Japanese counts things differently depending on the shape of the object. You attach a "counter" word to the number, and the trick is that a few combinations have sound changes (ichi + hon becomes ippon, etc.). You will not master all of these before the trip, and you do not need to. Learn generic "tsu" for 1-10 first — it bails you out almost everywhere ("kore hitotsu kudasai" = "this one, please"). Then pick up nin/mei for restaurants, mai for tickets, and hai for drinks. The rest is bonus. The irregular forms (in bold below) are the only real homework.
Generic ~つ (tsu) — your safety net, 1-10
The universal counter for objects when you don't know the right one. Works for food, items, vague things. Stops at 10 (after that, just use the bare number). 'Kore o hitotsu kudasai' (this one, please) will get you through most of the trip.
~個 (ko) — small/round objects
For small compact items: pieces of fruit, eggs, croquettes, onigiri, small packaged goods. Overlaps heavily with 'tsu' — if you forget 'ko', 'tsu' works fine. Watch ikko, rokko, jukko.
~枚 (mai) — flat thin things: tickets, stamps, paper
For anything flat: train tickets, museum tickets, postcards, stamps, plates, T-shirts, banknotes. Fully regular — no sound changes. Very tourist-useful at ticket machines and counters.
~本 (hon) — long cylindrical things: bottles, drinks
For long thin objects: bottles, cans of drink, umbrellas, pens, bananas, train lines. Spelling is always 本 but the reading flips between -hon / -bon / -pon. These sound changes are the classic ones worth memorizing.
~杯 (hai) — cups & glasses (drinks served in a vessel)
For drinks IN a cup/glass/bowl: a glass of beer, a cup of coffee, a bowl of rice/ramen. Different from 'hon' (a bottle) — 'hai' is the served portion. Reading flips -hai / -bai / -pai.
~人 (nin) / ~名 (mei) — people (use this at restaurants!)
THE one to nail before you go. Staff at restaurants ask 'Nanmei-sama desu ka?' (how many in your party?). You answer with -nin, or hold up fingers. -mei is the polite form staff use about you; you'll mostly say -nin. Note the two irregulars: one person and two people.
~泊 (haku) — nights of a hotel stay
Counts nights of lodging — useful at hotel check-in or when booking. Often paired with -nichikan (days). Reading flips -haku / -paku. 'Ippaku' = one night is the one you'll say most.
~階 (kai) — floors of a building
Reading floors in department stores, station buildings, and elevators. Reading flips -kai / -gai. Note: ground floor is the 1st floor (1階) in Japan — there's no separate 'ground floor'. Basement floors use 地下 (chika): B1 = 地下一階 (chika ikkai).