thirty; 30
Standard numeral for the quantity thirty.
このクラスには三十人の学生がいます。
There are thirty students in this class.
The late-night program ends at 30:00 (6 a.m.).
三十ページまで読んでください。
Please read up to page thirty.
6am
Only when written ３０
Colloquial use of 30 to mean 6:00 a.m., from the 30th hour of a 24+ hour clock system sometimes used in late-night scheduling. Restricted to the Arabic numeral spelling ３０.
明日の集合は３０時だって。つまり朝の６時だよ。
They said the meeting time tomorrow is 30 o'clock. That means 6 a.m.
三十 means thirty while 二十 means twenty; the two look alike as tens-numbers (Ｘ十) and are easy to misread quickly.
三十 means thirty while 四十 means forty; both follow the same Ｘ十 pattern for multiples of ten and can be confused when read fast.
Standard kanji spelling; high-frequency in news and general use.
Archaic single-character form for thirty; not used in modern Japanese.
Common Arabic numeral spelling, especially in horizontal writing and for the colloquial time sense.
Kanji with a zero marker; sometimes seen in vertical writing or formal contexts.
Formal legal/financial kanji (daiji); rarely used in everyday writing.
Archaic variant of 卅; essentially obsolete.
Compound of 三 (san, 'three') and 十 (jū, 'ten'). The reading みそ is an older native Japanese form, now obsolete.