A formula, not a factor
Lengths and weights all start from zero, so converting them is one multiplication. Temperature scales start from different places: water freezes at 0 °C, 32 °F and 273.15 K. So each conversion is a multiply and an add, shown under the boxes as you go, for example °F = °C × 9/5 + 32.
Points worth knowing
Water freezes at 0 °C (32 °F) and boils at 100 °C (212 °F) at sea level. Body temperature is about 37 °C (98.6 °F). A warm day of 25 °C is 77 °F. The two scales meet at −40, where −40 °C and −40 °F are the same temperature.
Kelvin
Kelvin starts at absolute zero, the coldest anything can be: 0 K is −273.15 °C or −459.67 °F. A step of 1 K is the same size as 1 °C, so a change reads the same in both. Kelvin is written without a degree sign.
One pair at a time
The pairs people look up most have a page each, opened on that pair with a table of common values: Celsius to Fahrenheit and Fahrenheit to Celsius.
Questions
Can I convert a change in temperature?
Not directly. The converter treats every number as a reading on a thermometer, so 10 °C becomes 50 °F. A rise of 10 °C is a rise of 18 °F: multiply a difference by 9/5 and leave out the 32.
What about Rankine or Réaumur?
They are not included. Only Celsius, Fahrenheit and Kelvin are in the list.