Convert Integers to Words

10²¹ − 1 = 999,999,999,999,999,999,999 (999 quintillion). Scales used: thousand (10³), million (10⁶), billion (10⁹), trillion (10¹²), quadrillion (10¹⁵), quintillion (10¹⁸). All arithmetic is BigInt-accurate; JavaScript’s regular Number type would silently round past 2^53 ≈ 9 × 10¹⁵.

JavaScript’s Number type is a 64-bit float. It can represent integers exactly only up to 2^53 – 1 = 9,007,199,254,740,991. Past that, precision degrades silently. 123456789012345678 + 1 returns 123456789012345680, not the correct result. BigInt avoids all that – every digit stays accurate up to our 10²¹ cap.

Two phrasings: “negative forty-two” (formal default) or “minus forty-two” (mathematical). Both are standard English. The sign is detected on the input string, the absolute value is converted, and the prefix is prepended.

Standard English: yes. Numbers 21 through 99 (except multiples of 10) hyphenate: twenty-one, forty-five, ninety-nine. We hyphenate by default. Turn off for informal writing or when downstream tools require space-separated words.

British English inserts “and” between the hundreds and the rest: “one hundred and twenty-three.” American English drops it. Both are widely understood; UK style is required for some British legal contexts and arithmetic-class conventions.

Title Case capitalizes every word (“Forty-Two”, “One Hundred Twenty-Three”) including the part after a hyphen. Sentence case only capitalizes the first letter of the first word (“Forty-two”). Title Case is for headings; Sentence case is for running text.

Yes – that’s a primary use case. For US checks, use Sentence case with hyphens on. The output for $1,234.56 would be “One thousand two hundred thirty-four”. Most banks accept either US or UK convention; pick what matches your bank’s preference.

No. All conversion runs in your browser using BigInt arithmetic and string lookups. Open DevTools → Network and watch zero requests fire after the page loads. Safe for payroll numbers, financial documents, or anything private.

A 100-line batch converts in under 50 ms on a modern laptop, even with trillion-sized numbers. The BigInt chunking is O(log₁₀₀₀ N) per number – bounded constant work for any practical input.

Yes. Total bundle is under 20 KB (HTML + CSS + JS, no external libraries). Once the page loads, disconnect and keep converting. Bookmark and use on flights, trains, or air-gapped machines.