数to単語

What is 数to単語?

A number-to-words converter spells a numeral out in English words — for example, 1234 becomes "one thousand two hundred thirty-four". This is used on checks, legal documents, and invoices where a written amount reduces ambiguity and fraud risk. The tool handles integers and, optionally, decimals (expressing the fractional part as cents or a fraction). All conversion runs locally in the browser.

How It Works

The converter decomposes the integer into groups of three digits (units, thousands, millions, billions, etc.) using division and modulo. Each group is rendered into words using a lookup table for 0-19 and the tens multiples (20, 30, ..., 90), then combined with the appropriate scale word (thousand, million). Negative numbers are prefixed with "minus". Decimal fractions are rendered digit-by-digit or as "and N/100" for check-style amounts. The result is lowercased and hyphenated per English convention.

Common Use Cases

• Writing checks — spell the dollar amount to deter alteration
• Filling legal and financial documents — express amounts in words where required
• Generating invoices and receipts — show amounts in both figures and words
• Creating educational materials — display number words for early numeracy exercises

Technical Details

Range: integers up to the JavaScript safe-integer limit (2^53 - 1, ~9 quadrillion) with named scales through quintillions. Grouping: 3-digit groups with scale words (thousand, million, billion, ...). Hyphenation: twenty-one through ninety-nine use a hyphen. Negative numbers prefix "minus". Decimal handling renders the fractional part digit-by-digit or as cents. The algorithm is O(digits) and runs locally.