英語の数字と日付：完全ガイド

基数

"one hundred"

the number 100, written as a word

"There are one hundred students in the auditorium."

基数

"a thousand"

1,000 — use "a" instead of "one" in informal speech

"The ticket costs a thousand dollars."

基数

"two million"

2,000,000 — no plural -s on "million" after a number

"The city has two million inhabitants."

基数

"twenty-one"

compound numbers 21–99 are hyphenated

"She turned twenty-one last Friday."

基数

"nought / zero"

the number 0 — "nought" (BrE), "zero" (AmE)

"The temperature dropped to zero overnight."

基数

"a dozen"

twelve items — informal collective expression

"Can you buy a dozen eggs on your way home?"

基数

"a score"

twenty — formal or literary

"Four score and seven years ago…"

基数

"oh"

spoken form of 0 in phone numbers, room numbers, and years

"Call me on oh-seven-seven-oh-three."

序数

"first (1st)"

position number one in a sequence

"She finished first in the race."

序数

"second (2nd)"

position number two in a sequence

"He came second in the spelling contest."

序数

"third (3rd)"

position number three — irregular spelling

"The third chapter is the most important."

序数

"twenty-first (21st)"

ordinal for 21 — hyphenate and use -st suffix

"The meeting is on the twenty-first of June."

序数

"hundredth (100th)"

ordinal for 100 — add -th to "hundred"

"This is the hundredth episode of the podcast."

序数

"on the + ordinal + of"

standard British date spoken format

"The concert is on the fifth of March."

序数

"nth degree"

an extreme or unspecified ordinal position

"He rehearsed his speech to the nth degree."

序数

"in the Xth place"

formal way to present ranked arguments

"In the first place, the data is unreliable."

分数とパーセント

"one half (½)"

one part of two equal parts — also "a half"

"Mix one half cup of flour with two eggs."

分数とパーセント

"one third (⅓)"

one part of three equal parts

"About one third of the budget goes to marketing."

分数とパーセント

"three quarters (¾)"

three parts of four equal parts

"Three quarters of the team agreed with the plan."

分数とパーセント

"two fifths"

two parts of five equal parts

"Two fifths of respondents prefer online learning."

分数とパーセント

"per cent / percent"

parts per hundred — BrE two words, AmE one word

"Sales rose by fifteen percent last quarter."

分数とパーセント

"percentage point"

a difference of 1% in absolute terms (not relative)

"Unemployment fell by two percentage points."

分数とパーセント

"decimal point"

the dot separating whole number from fraction

"The rate is three point five percent."

分数とパーセント

"ratio of X to Y"

the proportional relationship between two quantities

"The ratio of students to teachers is twenty to one."

日付とフォーマット

"MM/DD/YYYY"

American date format: month first, then day, then year

"The contract was signed on 06/18/2026."

日付とフォーマット

"DD/MM/YYYY"

British date format: day first, then month, then year

"The bill is dated 18/06/2026."

日付とフォーマット

"June 18, 2026"

American written format — month name, day, comma, year

"Please respond by June 18, 2026."

日付とフォーマット

"18 June 2026"

British written format — no comma between month and year

"The event takes place on 18 June 2026."

日付とフォーマット

"ISO 8601 (YYYY-MM-DD)"

international standard format for data and documents

"The log entry shows 2026-06-18T09:00:00Z."

日付とフォーマット

"in + month/year"

use "in" for months, years, seasons, and centuries

"The report was published in March 2025."

日付とフォーマット

"on + specific date"

use "on" for specific calendar dates and named days

"We will meet on Monday, June 22nd."

日付とフォーマット

"BC / AD / BCE / CE"

era designations in historical dates

"The pyramid was built around 2560 BC."

時間表現

"quarter past / quarter to"

BrE expressions for :15 and :45 minutes

"The train leaves at quarter past seven."

時間表現

"half past"

BrE expression for :30 minutes past the hour

"Dinner is at half past six."

時間表現

"a.m. / p.m."

before noon and after noon in 12-hour clock format

"The meeting starts at 9:30 a.m."

時間表現

"24-hour clock"

hours 0–23 used in military, transport, and formal contexts

"Departure is scheduled for 14:45."

時間表現

"o'clock"

exact hour with no minutes — apostrophe replaces missing letters

"Please be here at nine o'clock sharp."

時間表現

"noon / midnight"

precise terms for 12:00 p.m. and 12:00 a.m.

"Submissions close at midnight on Friday."

時間表現

"in the morning / afternoon / evening"

general time-of-day phrases used with a.m./p.m. context

"She usually exercises in the morning."

時間表現

"at dawn / at dusk"

literary or precise expressions for sunrise/sunset time

"The fishermen set out at dawn."

大きな数

"billion"

1,000,000,000 — one thousand million in modern English

"The company is valued at five billion dollars."

大きな数

"trillion"

1,000,000,000,000 — one million million

"Global GDP exceeds 100 trillion dollars."

大きな数

"million vs. millions of"

no -s after a number; add -s + "of" without a number

"Three million people watched. Millions of people watched."

大きな数

"tens of thousands"

an imprecise large quantity between 10,000 and 99,999

"Tens of thousands of fans attended the concert."

大きな数

"in the hundreds"

somewhere between 100 and 999 — informal estimate

"The complaints numbered in the hundreds."

大きな数

"roughly / approximately"

adverbs signalling an estimate rather than an exact figure

"The project cost approximately two million euros."

大きな数

"order of magnitude"

a factor of ten difference between two values

"The new model is an order of magnitude faster."

大きな数

"six-figure salary"

a salary between $100,000 and $999,999

"After the promotion she earned a six-figure salary."