Temperature Converter

Enter one temperature and all 5 scales fill in at once, because the conversion you need is rarely the one you expected to need. The Temperature Converter covers Celsius, Fahrenheit and Kelvin alongside Rankine, which engineering thermodynamics still uses, and Delisle, which runs backwards and is the reason the list is worth reading twice.

Every conversion pivots through Celsius rather than being hard-coded pair by pair. That keeps 20 possible conversions down to 10 short functions and means a rounding quirk cannot appear on one route and not another.

Six reference points sit at the foot, from absolute zero to a baking oven, each showing its Celsius and Fahrenheit values. Clicking one loads it into the input converted into whatever unit you currently have selected, which is a quicker way to sanity-check a scale you do not use daily than typing a number and hoping.

A Real Example: Body Temperature Across the Scales

Type 37 with °C selected. Fahrenheit returns 98.6, the familiar figure. Kelvin gives 310.15, since the two scales differ by a fixed 273.15 and share a degree size. Rankine gives 558.27, being Kelvin scaled by nine fifths. Delisle gives 94.5, and it falls as temperature rises, which is why boiling water sits at 0 on that scale and freezing water at 150.

The Formula Behind Each Scale

• Celsius to Fahrenheit multiplies by nine fifths and adds 32. The scales cross at -40, the one value that reads the same on both.
• Kelvin is Celsius plus 273.15 exactly, with no multiplication, because both use the same degree size. Rankine does the same job for Fahrenheit degrees and starts at absolute zero.
• Delisle is inverted and scaled by three halves from boiling point. It is the only scale here where a larger number means a colder temperature.
• Values are shown to 4 decimal places with trailing zeros trimmed, and anything at or above 1000, or below 0.001, switches to exponential notation to stay readable.
• Nothing prevents a value below absolute zero. Enter -300 in Celsius and you get a negative Kelvin figure, which is physically meaningless and mathematically exactly what the formula says.
• The copy button on each row copies the value fixed to 4 decimals with its unit, so 98.6000 F rather than the trimmed form on screen.