Temperature scales are not simple ratios, so this converter uses exact formulas. It first turns your input into Celsius, then into every other scale: from Fahrenheit, °C = (°F − 32) × 5/9; from Kelvin, °C = K − 273.15; from Rankine, °C = (°R − 491.67) × 5/9. Going back out: °F = °C × 9/5 + 32, K = °C + 273.15, and °R = (°C + 273.15) × 9/5. Handy reference points: water freezes at 0 °C = 32 °F = 273.15 K = 491.67 °R and boils at 100 °C = 212 °F = 373.15 K = 671.67 °R.
Kelvin and Rankine are absolute scales that start at absolute zero (−273.15 °C = −459.67 °F), where all thermal motion stops; Celsius and Fahrenheit can go negative. Kelvin shares the size of the Celsius degree, while Rankine shares the size of the Fahrenheit degree. Every result keeps 12 significant figures to remove floating-point noise. All math runs locally in your browser; nothing is uploaded.