25 °C in Fahrenheit
25 × 9/5 = 45, and 45 + 32 = 77. So 25 °C is 77 °F.
A useful approximation for mental arithmetic: double the Celsius value and add 30. That gives 80 here — close enough to judge the weather, though not to cook with.
Temperature converter
Convert a temperature between the four scales in use. You get the formula, the substitution and the same temperature expressed on every scale.
Result
Fill in the fields to see your result.
How it works
Temperature scales differ in two ways: the size of a degree, and where zero sits. Celsius and Kelvin share the same degree size and differ only by an offset of 273.15. Fahrenheit and Rankine share a smaller degree — exactly five-ninths of a Celsius degree — and also differ only by an offset.
That is why converting temperature is not like converting length. A metre is a pure scaling, so 0 m is 0 ft. A degree is a scaling plus a shift, so 0 °C is 32 °F. Any conversion that forgets the offset will be wrong by a constant, which is the single most common mistake.
Kelvin and Rankine are absolute scales: their zero is the point at which molecular motion stops, so negative values do not exist. This calculator refuses any input below that point, whichever scale you enter it in.
Formulas used
Celsius and Fahrenheit
°F = °C × 9/5 + 32 °C = (°F − 32) × 5/9
The 9/5 factor is the ratio of degree sizes; the 32 is the offset between the two zeros.
Absolute scales
K = °C + 273.15 °R = °F + 459.67 °R = K × 9/5
Worked examples
350 °F for an oven
(350 − 32) × 5/9 = 318 × 5/9 = 176.7 °C.
Most recipes round this to 175 °C or 180 °C, which is why oven dials rarely show the exact conversion.
Assumptions and limits
- Conversions use the exact defined relationships between scales; no rounding is applied before the final display.
- Water’s freezing and boiling points are quoted at standard atmospheric pressure.
- Values below absolute zero are rejected rather than converted.
Frequently asked questions
What is 100 °F in Celsius?
(100 − 32) × 5/9 = 37.8 °C. That is just above normal body temperature, which is why 100 °F is the traditional fever threshold in countries using Fahrenheit.
Is there a temperature where Celsius and Fahrenheit are equal?
Yes, exactly one: −40. Setting x = x × 9/5 + 32 gives x = −40, so −40 °C is −40 °F. It is the only crossing point of the two scales.
Why is Kelvin written without a degree symbol?
Because the kelvin is an SI base unit, not a degree on a scale with an arbitrary zero. Since 1967 the correct form is 300 K. Writing 300 °K is outdated.
What is Rankine used for?
It is the absolute counterpart of Fahrenheit, still used in some thermodynamics and engineering work in the United States. Zero rankine is absolute zero, and a rankine degree is the same size as a Fahrenheit degree.
Sources
- BIPM — The International System of Units (SI), definition of the kelvin
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