How to convert a unit
- Pick a category: Length, Weight, Volume, Area, Speed, or Temperature.
- Choose the units in each dropdown.
- Type a value into either field — the other updates instantly.
- Use the swap button to flip the two units without retyping.
Every conversion is a local calculation — no server round-trip, no delay waiting for a response.
Why unit conversion isn't always "just multiply"
Most unit conversions are a straightforward scale factor: multiply a value in one unit by a fixed ratio to get the equivalent in another. A mile is always exactly 1,609.344 meters; a pound is always exactly 0.45359237 kilograms. This tool stores each supported unit as a ratio to a base unit (meters for length, kilograms for weight, and so on) and converts by going through that base — convert to the base unit, then from the base unit to the target.
Temperature is the exception. Celsius, Fahrenheit, and Kelvin don't just use different-sized degrees — they have different zero points. 0°C is not the same physical temperature as 0°F (0°C is 32°F), so converting between them requires an offset calculation, not pure multiplication: Fahrenheit = Celsius × 9/5 + 32, not Celsius × some constant. This is a common source of manual conversion errors, and exactly the kind of arithmetic worth letting a tool handle.
A note on precision
Some common conversion factors are exact by international standard (an inch is defined as exactly 25.4mm, and everything else in the imperial length system derives from that). Others — most volume and weight conversions between metric and US customary units — are exact rational numbers but with enough decimal places that manual arithmetic invites rounding drift. This tool uses the full-precision conversion factors and only rounds for display, so chaining conversions (convert A→B, then B→C) stays accurate.
Metric vs. US customary: a quick reference
Nearly the entire world uses the metric system (meters, kilograms, liters, Celsius) for everyday measurement; the United States primarily uses US customary units (feet/miles, pounds, gallons, Fahrenheit) alongside metric in science, medicine, and some industries. Recipes, home improvement measurements, road signs, and body weight are the categories where US-based readers most often need a metric conversion — and where international readers most often need the reverse.
Privacy: what happens to your numbers
Every conversion is plain arithmetic running in your browser — nothing is sent anywhere, logged, or stored.