Currency
European Central Bank reference rates, updated each working day.
Same quantity, different words
1 lb 0.45359237 kg
Exact Not rounded, not measured — that is the definition of a pound, agreed in 1959. Every factor on this site is sourced the same way, and pages say when a figure is exact.
Length
Metres, feet, inches, miles and the rest of the distance family.
Weight & mass
Kilograms to pounds, grams to ounces, and the three different tons.
Temperature
Celsius, Fahrenheit, Kelvin and Rankine — offsets handled properly.
Volume
Litres, cups, pints and gallons — US and Imperial kept separate.
Area
Square metres, square feet, acres and hectares.
Speed
km/h, mph, knots, metres per second.
Pressure
Bar, psi, pascal, atmospheres — tyres to weather charts.
Energy
Joules, calories, kilowatt-hours, BTU.
Power
Watts, kilowatts, horsepower — metric and mechanical.
Time
Seconds to years, with a plain-English breakdown of the leftovers.
Digital storage
Bytes, kilobytes, megabytes — decimal (MB) and binary (MiB) both.
Angle
Degrees, radians, gradians, arcminutes.
Fuel economy
mpg and L/100 km — an inverse relationship, not a simple factor.
Why another converter
Most conversion sites give you a number and nothing else. This one shows the arithmetic, marks which factors are exact by definition, and refuses to pretend that a US gallon and an Imperial gallon are the same thing. Where a conversion has a trap in it — the three different tons, megabytes against mebibytes, miles per gallon running backwards — the page explains the trap instead of averaging it away.