How the numbers are checked

Last run 8 October 2026

A wrong answer key costs a teacher more than a missing one. So every Korean number this site shows or prints comes from one engine, and that engine is checked against a second program, written separately and built a different way, over every number it can produce.

What is checked

• Sino-Korean from 0 to 1,000,000, in the printed form spaced by 만 and in the solid form.
• Native Korean from 1 to 99, in the counting form and in the shortened form used before a counter.
• The Revised Romanization of every one of those.
• Every Hangul character, syllable by syllable: each must be a whole precomposed syllable (no loose jamo), must break down into the consonants and vowel the checker spells for it, and must sit where the rules allow. No 일 directly before 십, 백 or 천; one space exactly at the 만 boundary and nowhere else.

Result: 5,000,776 checks, none failed. The engine emits 42 distinct Hangul syllables in all.

Why the checker is independent

The checker was written before the engine, and differs from it on purpose. It does not contain a single typed Hangul syllable: every word is spelled out in its consonants and vowels and the syllables are assembled by the Unicode formula, so a typing slip in the engine cannot be matched by the same slip in the checker. It reads Sino-Korean numbers from the string of digits, four at a time, where the engine works by arithmetic. It romanizes by rewriting Latin letters at each join, where the engine works on Korean letters. A third, hand-typed table of forms from the sources is checked against both.

To show the checker can fail, fourteen faults were planted in copies of the engine, one at a time: 일십 for ten, 일만 for ten thousand, a missing or extra space, 륙 for six, 공 printed for zero, 여덟 typed in loose jamo, a misspelt native ten, 스물 살 for twenty years old, native numbers running to 100, and four romanization faults (16 as sibyuk, a million as baekman, 19 as yeolahop, 14 as yeolret). The checker caught all fourteen.

The decisions

Where Korean allows more than one form, this is what the site prints and what its answer keys accept.

Sources

• 국립국어원 (National Institute of Korean Language), 한글 맞춤법 (Korean spelling rules, 1988; current text 2017), 제43항, 제44항, 제52항.
• 국립국어원, 표준어 규정 (standard language rules), 제2부 표준 발음법, 제18항, 제20항, 제29항; 제1부 제6항 and 제17항.
• 국립국어원, 표준국어대사전 (Standard Korean Language Dictionary).
• 국어의 로마자 표기법 (Revised Romanization of Korean), Ministry of Culture and Tourism notice 2000-8; current text Ministry of Culture, Sports and Tourism notice 2014-42.
• Jaehoon Yeon and Lucien Brown, Korean: A Comprehensive Grammar (Routledge), chapters on numerals and classifiers.
• Ho-min Sohn, The Korean Language (Cambridge University Press, 1999).
• Wiktionary, Korean entries for 십육, 열여섯, 열하나, 열넷, 열아홉, 일흔 and 백만 (standard pronunciations and Revised Romanization, read 8 October 2026), used to confirm the sound rules on real words.

The engine and the checker are part of this site’s source. The worksheets on the printable page draw every word from the engine; nothing on a sheet is typed by hand.