Temperature Converter

What this tool is used for

• Moving one reading between Celsius, Fahrenheit and Kelvin without three separate conversions.
• Converting a scientific figure quoted in Kelvin into something intuitive.
• Checking an operating range that a datasheet gives in one scale against a requirement in another.
• Comparing weather, oven and laboratory figures in a single set of units.
• Converting a temperature for an audience that uses a different scale.

Frequently Asked Questions

Which scales are supported and how do they relate?

Celsius, Fahrenheit, Kelvin and Rankine. Kelvin and Celsius share a degree size (offset 273.15); Rankine and Fahrenheit share theirs (offset 459.67). So conversions between same-size scales are pure offsets, and only crossing families needs the 9/5 factor.

Why does Kelvin have no degree symbol?

Because it is an absolute unit, not a scale of degrees — SI writes 300 K, never 300°K. The symbol was formally dropped in 1967. Rankine is written °R and retains it, which is a genuine inconsistency.

What is absolute zero in each scale?

0 K, −273.15°C, −459.67°F and 0°R. It is a floor, not merely a very low temperature: it is unreachable in principle, and the third law of thermodynamics says no finite process can get there.

Do temperature differences convert the same way?

No, and this is the most common error. Differences use only the SCALE factor, never the offset: a 10°C rise is an 18°F rise and a 10 K rise. Applying the +32 to an interval produces nonsense.

Why is 37°C often written as 98.6°F?

It is a false-precision artefact. The original 19th-century measurement was 37°C to two significant figures; converting gives 98.6, which implies a precision the source never had. Modern studies put average body temperature nearer 36.6°C.

At what temperature do Celsius and Fahrenheit agree?

−40, the single point where the two scales cross. It is a useful sanity check on a conversion — if −40 does not map to −40, the formula has the offset and the ratio the wrong way round.

What is the Rankine scale?

An absolute scale using Fahrenheit-sized degrees, so it starts at absolute zero like Kelvin but counts in Fahrenheit increments. It survives in some US engineering thermodynamics work and almost nowhere else.

Common errors and gotchas

• Applying the Fahrenheit offset to a Kelvin conversion, where the offset is 273.15 and there is no 9/5 factor.
• Converting a temperature difference as if it were a temperature, which wrongly includes the offset.
• Writing degrees Kelvin. It is kelvin, without the degree sign, because it is an absolute scale.
• Rounding at an intermediate step, which the 9/5 factor then amplifies.
• Producing a Kelvin value below zero and not recognising that as impossible rather than merely cold.