Number to Words Converter Guide: Rules, Edge Cases & Examples

Basic Number Naming Rules

English has unique words for numbers one through nineteen. After that, it switches to a compound system: twenty, thirty, forty, and so on, combined with the ones digit using a hyphen (twenty-one, thirty-five, ninety-nine).

Numbers above 99 introduce place value words: hundred, thousand, million, billion. The system groups digits in threes from right to left, and each group gets its scale name. The number 4,567,890 breaks down as: four million, five hundred sixty-seven thousand, eight hundred ninety.

The Hyphen Rule

Compound numbers between 21 and 99 always get a hyphen when written as words. Forty-two. Seventy-eight. Ninety-nine. This applies everywhere the number appears, including within larger numbers: “three hundred forty-two.”

Do not hyphenate hundreds or thousands. It’s “one hundred,” not “one-hundred.” It’s “two thousand,” not “two-thousand.” The only hyphens go between the tens and ones positions.

The “And” Question

American English convention: do not use “and” in whole numbers. Say “one hundred fifty,” not “one hundred and fifty.” Reserve “and” for the decimal point: “one hundred and 50/100” (on checks) or “three and one-quarter.”

British English takes the opposite approach. “One hundred and fifty” is standard in the UK, Australia, and most Commonwealth countries. Neither convention is wrong — just be consistent.

Large Number Scale Words

The US, UK, Canada, and Australia all use the short scale. Most of continental Europe and Latin America use the long scale, where a billion equals a million million (10¹²). This discrepancy has caused real confusion in international finance and journalism.

Writing Numbers on Checks

Checks require the dollar amount in both digits and words. The legal amount is the one written in words, so accuracy matters. Write the full dollar amount, add “and,” then write cents as a fraction over 100.

Example: $2,347.89 becomes “Two thousand three hundred forty-seven and 89/100 dollars.” Start at the left edge of the line, use a capital first letter, and draw a line through remaining space to prevent alterations.

When to Use Words vs. Digits

The AP Stylebook says: spell out one through nine, use digits for 10 and above. The Chicago Manual of Style says: spell out one through one hundred plus round numbers (two hundred, three thousand). Legal writing often spells out numbers and follows with digits in parentheses: “thirty (30) days.”

Always spell out a number that begins a sentence. “Forty-seven people attended” — never “47 people attended” at the start. If the number is unwieldy (“Three thousand four hundred twenty-seven people attended”), restructure the sentence to avoid starting with it.

Frequently Asked Questions

When should I write numbers as words vs. digits?

Most style guides say to write out numbers one through nine (or one through ninety-nine in Chicago Manual) and use digits for larger numbers. Always write out numbers at the start of a sentence.

How do you write large numbers in words?

Break the number into groups of three digits from right to left. Name each group with its scale word: thousand, million, billion, trillion. For example, 2,500,000 is “two million five hundred thousand.”

What is the difference between short scale and long scale?

In the short scale (US, UK, Canada), a billion is 10&sup9;. In the long scale (most of continental Europe), a billion is 10¹². This means a “billion” in France is a “trillion” in the US.

How do you write a check amount in words?

Write the dollar amount in words, add “and,” then write cents as a fraction over 100. For $1,250.75: “One thousand two hundred fifty and 75/100 dollars.”

Do you use hyphens in number words?

Hyphenate compound numbers from twenty-one through ninety-nine. Numbers above one hundred do not use hyphens between hundreds and tens: “one hundred forty-two,” not “one-hundred-forty-two.”