Nihon-shiki or Nippon-shiki Rōmaji is a romanization

Romanization

In linguistics, romanization or latinization is the representation of a written word or spoken speech with the Roman script, or a system for doing so, where the original word or language uses a different writing system . Methods of romanization include transliteration, for representing written...

 system for transliterating the Japanese language

Japanese language

is a language spoken by over 130 million people in Japan and in Japanese emigrant communities. It is a member of the Japonic language family, which has a number of proposed relationships with other languages, none of which has gained wide acceptance among historical linguists .Japanese is an...

 into the Latin alphabet

Latin alphabet

The Latin alphabet, also called the Roman alphabet, is the most recognized alphabet used in the world today. It evolved from a western variety of the Greek alphabet called the Cumaean alphabet, which was adopted and modified by the Etruscans who ruled early Rome...

. In discussion about romaji, it is abbreviated as Nihon-shiki or Nippon-shiki. Among the major romanization systems for Japanese, Nippon-shiki is the most regular, and has a one-to-one relation to the kana

Kana

Kana are the syllabic Japanese scripts, as opposed to the logographic Chinese characters known in Japan as kanji and the Roman alphabet known as rōmaji...

 writing systems. In practice, Nippon-shiki has been largely supplanted by Hepburn romanization

Hepburn romanization

The is named after James Curtis Hepburn, who used it to transcribe the sounds of the Japanese language into the Latin alphabet in the third edition of his Japanese–English dictionary, published in 1887. The system was originally proposed by the in 1885...

.

It was invented by physicist Aikitsu Tanakadate (田中館 愛橘 Tanakadate Aikitsu) in 1885, and postdates the Hepburn

Hepburn romanization

The is named after James Curtis Hepburn, who used it to transcribe the sounds of the Japanese language into the Latin alphabet in the third edition of his Japanese–English dictionary, published in 1887. The system was originally proposed by the in 1885...

 system of romanization. Tanakadate's intention was to completely replace the traditional kanji

Kanji

Kanji are the adopted logographic Chinese characters hanzi that are used in the modern Japanese writing system along with hiragana , katakana , Indo Arabic numerals, and the occasional use of the Latin alphabet...

 and kana

Kana

Kana are the syllabic Japanese scripts, as opposed to the logographic Chinese characters known in Japan as kanji and the Roman alphabet known as rōmaji...

 system of writing Japanese with a romanized system, which he felt would make it easier for Japanese people to compete with Western countries. Since the system was intended for Japanese people to use to write their own language, it is much more regular than Hepburn romanization, and, unlike Hepburn's system, it makes no effort to make itself easier to pronounce for English speakers.

Nippon-shiki was followed by Kunrei-shiki

Kunrei-shiki

is a Japanese romanization system, i.e. a system for transcribing the Japanese language into the Latin alphabet. It is abbreviated as Kunrei-shiki. Its name is rendered Kunreisiki using Kunrei-shiki itself....

. Kunrei is otherwise nearly identical, but it merges the syllable pairs di/zi ぢ/じ, du/zu づ/ず, dya/zya ぢゃ/じゃ, dyu/zyu ぢゅ/じゅ, dyo/zyo ぢょ/じょ, wi/i ゐ/い, we/e ゑ/え, kwa/ka くゎ/か, gwa/ga ぐゎ/が, whose pronunciations in modern standard Japanese have become identical. For example, the word かなづかい, rendered kanadukai in Nippon-shiki, is pronounced as kanazukai in modern Japanese and romanized as such in Kunrei.

Nippon-shiki is considered the most regular of the romanization systems for the Japanese language, because it maintains a strict "one kana, two letters" form. Because it has unique forms corresponding to each of the respective pairs of kana homophones listed above, it is the only formal system of romanization that allows lossless ("round trip") mapping; see the hiragana

Hiragana

is a Japanese syllabary, one basic component of the Japanese writing system, along with katakana, kanji, and the Latin alphabet . Hiragana and katakana are both kana systems, in which each character represents one mora...

 article for more details.

Nippon-shiki has been established by the International Organization for Standardization

International Organization for Standardization

The International Organization for Standardization , widely known as ISO, is an international standard-setting body composed of representatives from various national standards organizations. Founded on February 23, 1947, the organization promulgates worldwide proprietary, industrial and commercial...

 in the ISO 3602 strict form. The JSL system, which is intended for use instructing foreign students of Japanese, is also based on Nippon-shiki.

Nipponsiki—ISO 3602 Strict

gojūon Gojuon The is a Japanese ordering of kana.It is named for the 5×10 grid in which the characters are displayed, but the grid is not completely filled, and, further, there is an extra character added outside the grid at the end: with 5 gaps and 1 extra character, the current number of distinct kana in a...					yōon Yoon is a feature of the Japanese language in which a mora is formed with an added sound.Yōon are represented in hiragana using a kana ending in i, such as き , plus a smaller-than-usual version of one of the three y kana, ya, yu or yo. For example kyō, "today", is written きょう, using a small version of...
あ/ア a	い/イ i	う/ウ u	え/エ e	お/オ o	(ya)	(yu)	(yo)
か/カ ka	き/キ ki	く/ク ku	け/ケ ke	こ/コ ko	きゃ/キャ kya	きゅ/キュ kyu	きょ/キョ kyo
さ/サ sa	し/シ si	す/ス su	せ/セ se	そ/ソ so	しゃ/シャ sya	しゅ/シュ syu	しょ/ショ syo
た/タ ta	ち/チ ti	つ/ツ tu	て/テ te	と/ト to	ちゃ/チャ tya	ちゅ/チュ tyu	ちょ/チョ tyo
な/ナ na	に/ニ ni	ぬ/ヌ nu	ね/ネ ne	の/ノ no	にゃ/ニャ nya	にゅ/ニュ nyu	にょ/ニョ nyo
は/ハ ha	ひ/ヒ hi	ふ/フ hu	へ/ヘ he	ほ/ホ ho	ひゃ/ヒャ hya	ひゅ/ヒュ hyu	ひょ/ヒョ hyo
ま/マ ma	み/ミ mi	む/ム mu	め/メ me	も/モ mo	みゃ/ミャ mya	みゅ/ミュ myu	みょ/ミョ myo
や/ヤ ya		ゆ/ユ yu		よ/ヨ yo
ら/ラ ra	り/リ ri	る/ル ru	れ/レ re	ろ/ロ ro	りゃ/リャ rya	りゅ/リュ ryu	りょ/リョ ryo
わ/ワ wa	ゐ/ヰ wi		ゑ/ヱ we	を/ヲ wo
				ん/ン n-n
voiced sounds (dakuten Dakuten , colloquially ten-ten , is a diacritic sign most often used in the Japanese kana syllabaries to indicate that the consonant of a syllable should be pronounced voiced. Handakuten , colloquially maru , is a diacritic used with the kana for syllables starting with h to indicate that they should... )
が/ガ ga	ぎ/ギ gi	ぐ/グ gu	げ/ゲ ge	ご/ゴ go	ぎゃ/ギャ gya	ぎゅ/ギュ gyu	ぎょ/ギョ gyo
ざ/ザ za	じ/ジ zi	ず/ズ zu	ぜ/ゼ ze	ぞ/ゾ zo	じゃ/ジャ zya	じゅ/ジュ zyu	じょ/ジョ zyo
だ/ダ da	ぢ/ヂ di	づ/ヅ du	で/デ de	ど/ド do	ぢゃ/ヂャ dya	ぢゅ/ヂュ dyu	ぢょ/ヂョ dyo
ば/バ ba	び/ビ bi	ぶ/ブ bu	べ/ベ be	ぼ/ボ bo	びゃ/ビャ bya	びゅ/ビュ byu	びょ/ビョ byo
ぱ/パ pa	ぴ/ピ pi	ぷ/プ pu	ぺ/ペ pe	ぽ/ポ po	ぴゃ/ピャ pya	ぴゅ/ピュ pyu	ぴょ/ピョ pyo
くゎ/クヮ kwa
ぐゎ/グヮ gwa

Note:

• Letters in red are obsolete in modern Japanese.
• When he へ is used as a particle it is written he not e (Kunrei-shiki/Hepburn).
• When ha は is used as a particle it is written ha not wa.
• When wo を is used as a particle it is written wo not o.
• Long vowels are indicated by a circumflex
  Circumflex
  The circumflex is a diacritic used in the written forms of many languages, and is also commonly used in various romanization and transcription schemes. It received its English name from Latin circumflexus —a translation of the Greek περισπωμένη...
  
  , for example long o is written ô, unlike Hepburn, which uses a macron
  Macron
  A macron, from the Greek , meaning "long", is a diacritic placed above a vowel . It was originally used to mark a long or heavy syllable in Greco-Roman metrics, but now marks a long vowel...
  
  .
• Syllabic n ん is written as n before consonants but as n' before vowels and y.
• Geminate consonants are marked by doubling the consonant following the sokuon
  Sokuon
  The is a Japanese symbol consisting of a small hiragana or katakana tsu. In less formal language it is called or , meaning "little tsu". Compare to a full-sized tsu:The sokuon is used for various purposes...
  
  , っ, without exception.