How PlainConvert works

What this is

PlainConvert is a small set of everyday converters: cups to grams, miles to kilometres, Fahrenheit to Celsius, kilograms to pounds, percentage change, Unix timestamps, Base64, JSON. The kind of thing you Google two or three times a week.

Most converter sites work, technically, but feel hostile: cookie banners, three ads above the input, a sidebar of two hundred half-broken tools, an explanation written for search engines rather than people. PlainConvert is the opposite. One thing per page, a clear input, a clear output, a sentence or two of context, and a small reference table for the values people actually look up.

Privacy

Everything runs in your browser. No values you type are sent to a server. No analytics, no cookies, no fingerprinting, no sign-up. The site is plain HTML, CSS, and a small amount of JavaScript — you can read it all by viewing source.

How the maths works

Each conversion uses published constants:

• Length and mass: the international yard and pound agreement (1959) — 1 inch is exactly 2.54 cm, 1 pound is exactly 0.45359237 kg.
• Temperature: the standard linear relationship between the Fahrenheit and Celsius scales.
• Fuel economy: US gallons (3.78541 L) and the international mile (1.609344 km).
• Cooking: per-ingredient densities cross-checked against USDA FoodData Central and the King Arthur Baker's ingredient weight reference. Cooking weights are inherently approximate — measuring methods vary, and humidity affects flour and sugar — so use these as a starting point, not a guarantee.
• Bytes: decimal (KB = 1,000 bytes) and binary IEC (KiB = 1,024 bytes) shown side by side.

What is missing

By design, PlainConvert does not try to be a complete unit database. It covers the conversions most people look up most days. If you want every obscure unit in physics, chemistry, and engineering, there are exhaustive sites for that. PlainConvert chooses depth over breadth on the units people actually need.

Built with

Plain static HTML, CSS, and JavaScript. No framework, no build dependencies, no analytics. The site is generated by a small Node script and served as static files. Typography is Satoshi from Fontshare, with JetBrains Mono for code.