A temperature converter moves a reading between Celsius, Fahrenheit and Kelvin (plus Rankine for engineering). Temperature is different from length or weight: because Celsius and Fahrenheit each start their zero at a different point, you can't just multiply — you need a scale factor of 9/5 and an offset. The cleanest approach is to pivot everything through Celsius, which is exactly what this tool does, so one input lights up all four scales at once.
Reviewed: June 20, 2026 · Author: Naveen P N, Founder — AI Calculator · Verified against: the standard scale definitions, recomputed in code.
The conversion formulas
To convert any pair, first turn the input into Celsius — subtract 32 and scale by 5/9 for Fahrenheit, or subtract 273.15 for Kelvin — then build the others back out. The 9/5 factor reflects that a Celsius degree is 1.8 times the size of a Fahrenheit degree; the 32 and 273.15 offsets line up the zero points. Kelvin and Rankine are absolute scales whose zero is absolute zero, the coldest possible temperature.
Worked example — 100 °C across the scales
Scenario: convert 100 °C (boiling water) to every scale.
Boiling water is 100 °C = 212 °F = 373.15 K = 671.67 °R. The same machinery handles the everyday cases: 0 °C is 32 °F (freezing), 37 °C is 98.6 °F (body temperature), and the famous crossover where the scales agree is −40 °C = −40 °F. Because Kelvin starts at absolute zero, you'll never see a negative Kelvin value — a quick sanity check on any conversion.
Frequently Asked Questions
°F = °C × 9/5 + 32. 100 °C = 212 °F; 37 °C = 98.6 °F.
°C = (°F − 32) × 5/9. 32 °F = 0 °C; 98.6 °F = 37 °C.
K = °C + 273.15. 0 °C = 273.15 K; 100 °C = 373.15 K.
At −40: −40 °C = −40 °F exactly.
Absolute scale with °F-sized degrees: °R = K × 9/5 = °F + 459.67.