Japanese counter words (助数詞, josūshi) are obligatory classifiers attached to numbers when counting. The choice depends on the shape, type, or category of the thing being counted — long thin objects take 本, flat objects take 枚, small animals take 匹, machines take 台, and people take 人. This reference lets you search 60+ common counters by what they count.
How it works
Each entry pairs a counter with the category it covers, its reading, and an example. The tricky part of counters is the euphonic sound change after certain numbers, which the examples capture:
本 (hon, long thin objects): 1 いっぽん ippon, 3 さんぼん sanbon,
6 ろっぽん roppon, 8 はっぽん happon, 10 じゅっぽん juppon
人 (nin, people): 1 ひとり hitori, 2 ふたり futari, 3+ regular さんにん
匹 (hiki, small animals): 1 いっぴき ippiki, 3 さんびき sanbiki, 6 ろっぴき roppikiSearch matches against the counter kanji, its romaji reading, and the English category, so you can look up either direction.
Example and notes
To count three pencils you need the long-thin counter 本: 鉛筆三本 (enpitsu sanbon). To count two cats you need the small-animal counter 匹 with its irregular reading: 猫二匹 (neko nihiki). When in doubt for a general inanimate object up to ten, the native つ counter (一つ, 二つ …) is an acceptable fallback. This is a learner reference; some specialised counters (for gods, ships, bound volumes) have additional nuances beyond the example shown.