Converters
Currency conversion across 162 currencies with the mid-market rate, the inverse rate and the quote source shown for every figure.
2 tools
Converters fall into two families that behave very differently. Unit conversion is deterministic: an inch is exactly 25.4 millimetres by definition, so the same input always yields the same output and any disagreement between tools means one of them used a wrong constant. Currency conversion is the opposite — the rate is a market price with a timestamp and a source, so a figure without a date is not a number you can act on.
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Currency Converter
Convert between 162 currencies at the mid-market rate, with the inverse rate, a typical bank spread, and the quote date and source shown.
Unit Converter
Convert length, weight, temperature, area, volume, speed, data and time as you type, computed from the exact international definitions.
About Converters
Within units there is a further distinction worth knowing. Most conversions are a single multiplicative factor; temperature is not, because the scales have different zero points, which is why 0 °C is 32 °F but 0 °C is not twice 0 °F. Wherever possible the factors here use values fixed by the SI brochure or by national legislation rather than rounded approximations, so results agree to the precision you can type.
Everything runs in the browser, including the exchange rate bundled at build time. Nothing about your figures is sent anywhere.
Frequently asked questions
Which conversion factors are exact?
The definitional ones. The international inch has been exactly 25.4 mm since 1959; the pound is exactly 0.45359237 kg; a litre is exactly one cubic decimetre; the thermochemical calorie is exactly 4.184 J. One acre is 4046.8564224 m² by definition, and one US gallon is exactly 3.785411784 L — while the imperial gallon is a different number, which is why naming the variant matters. Where a factor is a measurement rather than a definition the result is quoted only to the precision the source supports.
Why is temperature handled differently from other units?
Because the scales do not share a zero point, so conversion is not multiplication. Celsius and Fahrenheit are related by an affine function: °F = °C × 9/5 + 32. Kelvin uses the same degree size as Celsius but starts at absolute zero, which is why adding temperatures in kelvin is meaningful while adding them in Celsius is not an absolute quantity. Routing temperature through a single reference scale prevents an offset scale being silently combined with a ratio scale.
Why do currency rates change, and which rate is used?
A currency pair is a traded price, quoted by banks and exchanges and moving continuously through the trading week. Unlike a unit factor it is not fixed by definition, so any usable figure needs three things: the value, the direction of the pair (which currency is the base), and the moment it was observed. The rate bundled here is shown with the date it was captured, next to the result. For anything consequential — a payment, an invoice, a contract — treat that date as the expiry of the number and confirm with your bank or payment provider.
Why does my calculator disagree with this one?
For units the cause is almost always a rounded constant on one side: using 2.2 lb/kg instead of 2.20462262 lb/kg introduces an error of about 0.2%, which is invisible in a recipe and material in an engineering quantity. For currency the cause is almost always timing or spread — a rate captured a day earlier, or a bank's customer rate with its margin built in, against an interbank mid rate. Check the assumptions before assuming an arithmetic error.
Do you cover unusual or historical units?
The coverage is the units that appear in everyday work and study: length, mass, temperature, area, volume, speed, data and time. Deliberately excluded are units whose definition varies by jurisdiction or era — the bushel, gallons other than the US and imperial forms, and historical units such as the league. Offering a name that means three different quantities in three countries would produce confident wrong answers, which is worse than not offering it at all.
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This space is reserved for a sponsor. Every tool on this site stays free and runs locally in your browser.