Number to Words Converter

Converting Numbers to Words

Converting numbers to their word equivalents is essential in many professional and legal contexts. Cheques, legal documents, invoices, and contracts often require amounts written in words to prevent fraud and misinterpretation. A handwritten digit can be altered — changing "1" to "7" or adding a zero — but a written-out amount like "one thousand two hundred and thirty-four dollars" is much harder to modify undetected.

Different English-speaking countries have subtle variations in number naming. American English typically omits "and" between hundreds and tens ("one hundred twenty-three"), while British English includes it ("one hundred and twenty-three"). The word "billion" historically meant different things: in American English, it's 10^9 (one thousand million), while in traditional British English, it was 10^12 (one million million). Today, most countries have adopted the American convention.

Ordinal Numbers

Ordinal numbers indicate position or order: first, second, third, fourth. Most ordinals follow a predictable pattern (adding "-th"), but several are irregular: first (not "oneth"), second (not "twoth"), third (not "threeth"), fifth (not "fiveth"), eighth (not "eightth"), ninth (not "nineth"), and twelfth (not "twelveth"). These irregularities trace back to Old English and must be memorized rather than derived from rules.

Currency in Words

Writing currency amounts in words follows specific conventions. The main unit is written in words, followed by the subunit. For US dollars: "one hundred and twenty-three dollars and forty-five cents." For British pounds: "one hundred and twenty-three pounds and forty-five pence." In Nigerian naira: "one hundred and twenty-three naira and forty-five kobo." Legal documents often include both forms: "$1,234.56 (one thousand two hundred and thirty-four dollars and fifty-six cents)."

Large Number Names

Beyond billions, number names become less commonly known. A trillion is 10^12, a quadrillion is 10^15, and the names continue: quintillion (10^18), sextillion (10^21), septillion (10^24), octillion (10^27), nonillion (10^30), and decillion (10^33). These names follow a Latin-based naming system. The largest named number in common use is a googol (10^100), which inspired the name of the company Google.

Programming Number-to-Words

Implementing number-to-words conversion in code is a classic programming challenge. The algorithm typically works by breaking the number into groups of three digits (hundreds, tens, ones) and processing each group, attaching the appropriate scale word (thousand, million, billion). Edge cases include zero, negative numbers, and very large numbers. Libraries exist in most programming languages: Python's num2words, JavaScript's number-to-words npm package, and Java's ICU NumberFormat.