Below absolute zero — not physically possible
Below absolute zero — not physically possible
Below absolute zero — not physically possible
Below absolute zero — not physically possible
Type a value into any one of the four fields and the other three update instantly — there's no separate "convert" step, and no field is more important than another. Temperature scales differ by their zero points and the size of one degree.
Celsius sets 0° at the freezing point of water and 100° at boiling point, and is the standard scale almost everywhere outside the US. Fahrenheit sets 32° at freezing and 212° at boiling, based on an older reference mixture, and is still used for everyday temperatures in the US. Kelvin and Rankine are absolute scales — 0 is absolute zero, the coldest temperature theoretically possible, with no negative values. Kelvin uses Celsius-sized degrees; Rankine uses Fahrenheit-sized degrees. Scientists and engineers use Kelvin (and occasionally Rankine in US engineering contexts) because absolute scales make calculations involving gas laws, thermodynamics and radiation much simpler.
°F = °C × 9/5 + 32. K = °C + 273.15. °Ra = (°C + 273.15) × 9/5. To go the other way: °C = (°F − 32) × 5/9, °C = K − 273.15, °C = °Ra × 5/9 − 273.15. This calculator uses Celsius internally as the common reference point and converts to and from it, regardless of which field you actually type into.
Absolute zero (−273.15°C, 0 K, −459.67°F, 0 Ra) is the lowest temperature theoretically possible — the point at which particles have minimal thermal motion. It can't be reached in practice, only approached extremely closely in laboratory conditions. If you enter a value that would convert to below −273.15°C, this calculator flags it as not physically possible rather than showing a misleading negative-Kelvin result.