Temperature Unit Converter

Convert with F = C × 9/5 + 32. So 0 °C is 32 °F (water freezes), 100 °C is 212 °F (water boils), 25 °C is 77 °F (room temperature in summer), and 37 °C is 98.6 °F (body temperature). The 9/5 factor accounts for Fahrenheit's smaller degrees, and the +32 shifts the freezing point. Calculators do this instantly. For mental approximation, double the Celsius and add 30 — gives a rough Fahrenheit (close enough for weather forecasts). For precision, always use the full formula and don't round intermediate values.

C = (F − 32) × 5/9. Subtract 32 first, then multiply by five-ninths. So 70 °F = (70 − 32) × 5/9 = 38 × 5/9 ≈ 21.1 °C — a comfortable room. 32 °F is exactly 0 °C, and 212 °F is exactly 100 °C, since the formula is the inverse of the Celsius-to-Fahrenheit version. The calculator handles the arithmetic cleanly. Quick mental shortcut: subtract 30, then halve — gives a rough Celsius. Use the proper formula for any precision work, especially in scientific calculations or medical contexts where small differences matter.

K = C + 273.15. Just add 273.15 to the Celsius value. So 0 °C = 273.15 K (water freezing point), 100 °C = 373.15 K (water boiling), 25 °C ≈ 298.15 K (room temperature). The size of one degree is identical in both scales — only the zero point differs. Kelvin starts at absolute zero, where molecular motion stops, while Celsius starts at water's freezing point. Many physics formulas (ideal gas law, blackbody radiation, Carnot efficiency) require kelvin because they involve absolute temperature ratios that don't make sense on a Celsius scale that allows negative values.

Two-step conversion: Kelvin → Celsius → Fahrenheit. First C = K − 273.15, then F = C × 9/5 + 32. Combined: F = (K − 273.15) × 9/5 + 32, which simplifies to F = K × 9/5 − 459.67. So 300 K = 80.33 °F, and 0 K (absolute zero) = −459.67 °F. The calculator does both steps internally and just shows the answer. Useful in engineering applications where data may be reported in kelvin (especially blackbody temperatures of furnaces or stars) but final reports use Fahrenheit. Direct conversion saves you from doing two steps manually.

K = R × 5/9. Rankine is the absolute version of Fahrenheit, used mainly in some American engineering disciplines. Both Rankine and Kelvin start at absolute zero, but Rankine uses Fahrenheit-sized degrees while Kelvin uses Celsius-sized degrees. So 540 R = 300 K, and 0 R = 0 K = absolute zero. Going the other way: R = K × 9/5. The relationship mirrors how Fahrenheit and Celsius differ in degree size, just shifted to start at absolute zero. Most physics problems stick with kelvin; Rankine appears mostly in older American thermodynamics textbooks and specific engineering codes.

Three core formulas connect the four common scales: F = C × 9/5 + 32 (Celsius to Fahrenheit), K = C + 273.15 (Celsius to Kelvin), R = F + 459.67 (Fahrenheit to Rankine). Inverse versions follow by simple algebra. Memorise the freezing and boiling points of water in each: 0/32/273.15/491.67 (freezing), and 100/212/373.15/671.67 (boiling). Once you know two reference points and the degree size relationship, any conversion is straightforward. Calculators handle conversions in any direction, but knowing the underlying relationships catches errors and helps with sanity checks.

Absolute zero is the temperature at which all classical molecular motion ceases — the lowest possible temperature. In kelvin: 0 K. In Celsius: −273.15 °C. In Fahrenheit: −459.67 °F. In Rankine: 0 R. You can never quite reach it, only approach it asymptotically — the third law of thermodynamics says so. Modern labs have cooled gases down to a few nanokelvin above absolute zero, where quantum effects like Bose-Einstein condensation appear. The reason temperature scales like Kelvin and Rankine are useful is that they avoid negative absolute temperatures, which would be physically meaningless.