Unit
Length, mass, temperature, data and time
Most unit conversions are a single multiplication by a defined factor. An inch is exactly 25.4 millimetres and a pound is exactly 0.45359237 kilograms — these are definitions rather than measurements, agreed internationally in 1959, so conversions between them are exact rather than approximate.
The exceptions are worth knowing. Temperature scales have different zero points, so Celsius to Fahrenheit needs an offset as well as a factor. Data sizes have two competing conventions, one based on powers of ten and one on powers of two, which is why a drive sold as one terabyte shows up smaller in an operating system. This converter covers length, mass, temperature, data and time.
How to use it
- Pick a categoryLength, mass, temperature, data or time. Keeping categories separate avoids the classic mistake of converting a quantity into a unit that does not measure the same thing.
- Enter a value and read the restEvery unit in the category updates at once, so you can see the value in all of them rather than converting twice to compare.
- Watch the precisionExact factors are used rather than rounded ones, so converting out and back returns the value you started with instead of drifting.
Frequently asked questions
How do I convert Celsius to Fahrenheit?
Multiply by 9/5 and add 32; reverse it by subtracting 32 first and then multiplying by 5/9. The offset exists because the two scales put zero in different places — water freezes at 0°C and 32°F. The scales cross at −40, which is the same temperature in both.
Is a kilobyte 1,000 or 1,024 bytes?
Both, depending on who is speaking. The SI prefix means 1,000, and that is what drive manufacturers use. Memory and many operating systems use 1,024, for which the correct name is kibibyte, KiB. The gap compounds with each prefix, reaching about 10% by terabyte — which is the whole explanation for a "1 TB" disk showing roughly 931 GB.
What is the difference between mass and weight?
Mass is how much matter something contains and does not change with location; weight is the force gravity exerts on that mass. Kilograms measure mass, newtons measure force. Everyday usage conflates them harmlessly on Earth, but converting pounds to kilograms is strictly a mass conversion.
Why do US and imperial gallons differ?
They descend from different historical standards and were never reconciled. A US liquid gallon is about 3.785 litres, an imperial gallon about 4.546 — a difference of roughly 20%. The same divergence affects pints and fluid ounces, so a recipe or a fuel figure needs to state which system it means.
Are conversion factors exact or approximate?
Length and mass conversions between imperial and metric are exact by definition. Others are not: a year is not a whole number of days, and a month has no fixed length at all, so any conversion involving them rests on a convention rather than a fact.