Teacher’s Introduction: Welcome to "The Matrix"

If you have been studying Japanese for a while, you know the feeling. You learn the number for "One" (ichi). But then you go to a restaurant, order one beer, and suddenly you have to say "ippai." You order one burger, and it’s "hitotsu." You say you have one friend, and it’s "hitori."

Why?!

As your teacher today, I am going to tell you the truth: Japanese is obsessed with categories. The language changes based on what you are counting and when it happens.

It looks scary, but there is a system. In this guide, we are going to break down the entire mathematical universe of Japanese: Numbers, Days, Weeks, Months, Time, and the dreaded Counters.

Grab a large coffee (ippai). Let’s do this.

Part 1: The Foundation (Numbers 0-10)

These are the "On-Yomi" (Chinese-derived) readings. You will use these for math, money, and phone numbers.

Number Kanji Reading Mnemonic
0 零 / ゼロ Zero It’s a loan word from English!
1 一 Ichi One finger holding up the line.
2 二 Ni Two lines. Easy.
3 三 San Three lines. (Santa says "San-San-San").
4 四 Yon / Shi Looks like a window with curtains.
5 五 Go Looks like a runner crossing the finish line "GO!"
6 六 Roku A person doing jumping jacks.
7 七 Nana / Shichi An upside down 7.
8 八 Hachi Looks like a volcano (Mt. Fuji).
9 九 Kyuu / Ku Looks like a person doing a pushup. Sounds like "Q".
10 十 Juu A plus sign. 10 is a "Plus".

Part 2: The "Native" Counting System (The 'Tsu' System)

Important: When you are counting "abstract things" (ideas, shapes, boxes, orders) or things that don't have a specific category, you cannot use Ichi/Ni/San. You must use the native Japanese system.

Teacher’s Note: You only need to memorize this up to 10. After 10, you switch back to normal numbers.

  1. Hitotsu (一つ) - "He toasts" to one success.
  2. Futatsu (二つ) - "Foo" fighter fights two people.
  3. Mittsu (三つ) - "Me too!" (Three sounds like Me).
  4. Yottsu (四つ) - Yo, that’s four!
  5. Itsutsu (五つ) - "It suits" (Itsutsu) you five times better.
  6. Muttsu (六つ)
  7. Nanatsu (七つ) - Nana loves seven.
  8. Yattsu (八つ) - Usually sounds like "Yacht".
  9. Kokonotsu (九つ) - Coco-nuts.
  10. Too (十) - Note: No "tsu" at the end! Just "Too".

Part 3: The Calendar (Time Travel)

This is where students get confused. We need to learn the Names of the days and the Relative Time (Past/Future).

A. The Days of the Week (Elements)

  • Sunday: 日曜日 (Nichiyoubi) – Sun Day
  • Monday: 月曜日 (Getsuyoubi) – Moon Day
  • Tuesday: 火曜日 (Kayoubi) – Fire Day
  • Wednesday: 水曜日 (Suiyoubi) – Water Day
  • Thursday: 木曜日 (Mokuyoubi) – Tree/Wood Day
  • Friday: 金曜日 (Kinyoubi) – Gold/Money Day
  • Saturday: 土曜日 (Doyoubi) – Earth/Soil Day

B. "Time Travel" (Relative Days)

You need to know how to say "Day after tomorrow."

English Kanji Reading Teacher's Hint
Day before Yesterday 一昨日 Ototoi Think "Oh... that was long ago."
Yesterday 昨日 Kinou "Key-no"
Today 今日 Kyou -
Tomorrow 明日 Ashita -
Day after Tomorrow 明後日 Asatte "Ah, satty" (Saturday is later).

Part 4: Months (Names vs. Duration)

A. Calendar Months (The Name)

This is easy! It is just Number + Getsu (月).

  • January: Ichigatsu (1月)
  • February: Nigatsu (2月)
  • April: Shigatsu (4月) — Watch out! Use "Shi" not "Yon".
  • July: Shichigatsu (7月) — Use "Shichi" not "Nana".
  • September: Kugatsu (9月) — Use "Ku" not "Kyuu".
  • December: Juunigatsu (12月)

B. Counting Duration (How long?)

To say "For two months," you add the small Katakana "Ka" (カ or ヶ) in the middle.

  • 1 Month Duration: Ikkagetsu (一ヶ月)
  • 2 Months Duration: Nikagetsu (二ヶ月)
  • 6 Months Duration: Rokkagetsu (六ヶ月) — Note the small 'tsu' jump!

C. Relative Months

  • Last Month: Sengetsu (先月)
  • This Month: Kongetsu (今月)
  • Next Month: Raigetsu (来月)

Part 5: Weeks (週 - Shuu)

A. Relative Weeks

  • Last Week: Senshuu (先週)
  • This Week: Konshuu (今週)
  • Next Week: Raishuu (来週)
  • Week after Next: Saraishuu (再来週)

B. Counting Weeks (Duration)

Just add "Kan" (間) which means "Interval."

  • For 1 Week: Isshuukan (一週間)
  • For 2 Weeks: Nishuukan (二週間)
  • For 3 Weeks: Sanshuukan (三週間)

Part 6: Days of the Month (The Crazy 1-10)

This is the hardest part of the calendar. The days from the 1st to the 10th have special names. You simply have to memorize these.

  • 1st: Tsuitachi (1日)
  • 2nd: Futsuka (2日)
  • 3rd: Mikka (3日)
  • 4th: Yokka (4日)
  • 5th: Itsuka (5日)
  • 6th: Muika (6日)
  • 7th: Nanoka (7日)
  • 8th: Youka (8日)
  • 9th: Kokonoka (9日)
  • 10th: Touka (10日)
  • 14th: Jyuu-yokka (Exception!)
  • 20th: Hatsuka (Big Exception!)
  • 24th: Nijuu-yokka (Exception!)
  • Rest are normal: 11th = Juuichi-nichi.

Part 7: The Clock (Time)

A. The Hours (時 - Ji)

  • 1:00 - Ichiji
  • 4:00 - Yoji (NOT Yonji, NOT Shiji) — Critical Warning!
  • 7:00 - Shichiji (NOT Nanaji)
  • 9:00 - Kuji (NOT Kyuuji)

B. The Minutes (分 - Fun/Pun)

  • 1 min: Ippun (1分) — (Jump sound)
  • 2 min: Nifun
  • 3 min: Sanpun — (Pun)
  • 4 min: Yonpun
  • 5 min: Gofun
  • 6 min: Roppun — (Jump sound)
  • 8 min: Happun — (Jump sound)
  • 10 min: Juppun — (Jump sound)

Part 8: The Ultimate "Counter" List (1-10 Examples)

Here is the deep dive. In Japanese, the sound of the number often changes to blend with the counter. We call these "Sound Changes."

Category 1: People (人 - Nin)

Exceptions are in Red/Bold.

  1. Hitori (Alone/1 Person)
  2. Futari (Pair/2 People)
  3. San-nin
  4. Yo-nin (Drop the 'n' from Yon)
  5. Go-nin
  6. Roku-nin
  7. Nana-nin
  8. Hachi-nin
  9. Kyuu-nin
  10. Juu-nin

Category 2: The "H" Group (Changes to P/B)

Applies to: Long things (本 - Hon), Cups (杯 - Hai), Small Animals (匹 - Hiki).

Let's use "Long Things" (Hon) as the example.

  1. Ippon (Jump + P)
  2. Ni-hon
  3. San-bon (Changes to B!)
  4. Yon-hon
  5. Go-hon
  6. Roppon (Jump + P)
  7. Nana-hon
  8. Happon (Jump + P)
  9. Kyuu-hon
  10. Juppon (Jump + P)

Category 3: The "K" Group

Applies to: Small Round Things (個 - Ko), Floors (階 - Kai), Frequency (回 - Kai), Houses (軒 - Ken).

Let's use "Small Round Things" (Ko) as the example.

  1. Ikko (Jump sound)
  2. Ni-ko
  3. San-ko
  4. Yon-ko
  5. Go-ko
  6. Rokko (Jump sound)
  7. Nana-ko
  8. Hakko (Jump sound)
  9. Kyuu-ko
  10. Jukko (Jump sound)

Category 4: The "S" Group

Applies to: Books (冊 - Satsu), Age (歳 - Sai), Shoes/Socks (足 - Soku).

Let's use "Age" (Sai) as the example.

  1. Issai (Jump sound)
  2. Ni-sai
  3. San-sai
  4. Yon-sai
  5. Go-sai
  6. Roku-sai
  7. Nana-sai
  8. Hassai (Jump sound)
  9. Kyuu-sai
  10. Jussai (Jump sound)

Category 5: The "Flat & Machine" Group (The Easy Ones!)

Applies to: Flat things (枚 - Mai), Machines/Vehicles (台 - Dai). These DO NOT change sounds. Just add the number.

  1. Ichimai / Ichidai
  2. Nimai / Nidai
  3. Sanmai / Sandai

Category 6: Thin & Long Things vs. Thin & Flat Things

  • Thin & Long (Cylindrical): Use Hon (本). (Pencils, Bottles, Trees, Umbrellas).
  • Thin & Flat (Paper-like): Use Mai (枚). (Paper, Shirts, Plates, Tickets).

Category 7: Order (番 - Ban)

  1. Ichiban (Number 1 / The Best)
  2. Niban
  3. Sanban

Conclusion: How to Master This Mess

Okay, student. Take a deep breath.

You just digested about 2,000 words worth of Japanese grammatical rules. It looks overwhelming, but the secret is patterns.

  • The "1, 6, 8, 10" numbers almost always have a "Jump" sound (Ikk-, Ropp-, Happ-, Jupp-).
  • The number 3 often changes "H" to "B" (San-bon).

Your Homework Assignment:

Don't try to memorize this whole blog post today. Bookmark this page. Use it as your dictionary.

  • Week 1: Master the "Tsuitachi to Touka" (1st-10th days).
  • Week 2: Master the "H" group counters (Hon/Hai/Hiki).
  • Week 3: Master the Clock.

Japanese is a beautiful language, but it requires patience. You are doing great.

Gambatte ne! (Good luck!)

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