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05 tools

Convert

Units, number bases, colour codes and CSV.

01Colour ConverterConvert colours between HEX, RGB and HSL with a live swatch and a light/dark contrast hint. Useful for design tokens and CSS.→02Unit ConverterConvert between metric and imperial units for length, mass, temperature, area, volume and speed, with exact factors.→03Number Base ConverterTurn a number between binary, octal, decimal and hexadecimal at once. Handles arbitrarily large integers without losing precision.→04Roman Numeral ConverterConvert 1–3999 into Roman numerals, or read a Roman numeral back as a number. Rejects malformed strings instead of guessing.→05CSV to JSON ConverterTurn comma or tab separated data into a JSON array of objects. Handles quoted fields, embedded commas and escaped quotes.→

Formats that refuse to agree

Conversion problems are rarely arithmetic. They are definitional: which gallon, which alphabet order, which decimal separator, whether the leading zero in a phone number survived. Each tool here is built around one of those disagreements, and each one shows what the input was actually understood to be rather than silently applying a rule.

Read the units before the number

The most expensive conversion errors come from using the right number with the wrong unit: a US cup of flour is 120 grams, an imperial one is closer to 140; a US gallon is 3.785 litres, an imperial one 4.546. If a result is off by 4% or 20%, the arithmetic was fine and the unit assumption was not. That is why every converter on this site names both sides of the conversion explicitly.

Colour and numbers are the same problem

Hex, RGB and HSL describe one colour in three coordinate systems, and base conversions describe one quantity in different bases. Neither is a transformation of meaning — only of notation, which is exactly why converting is safe and why the result is always the same value.