Temperature Converter

Use the formula: °F = °C × 9/5 + 32. For example, 25 °C = 25 × 1.8 + 32 = 45 + 32 = 77 °F. A quick mental shortcut: double the Celsius value, subtract 10%, then add 32 (so 25 °C → 50 − 5 + 32 = 77 °F).

Use the formula: °C = (°F − 32) × 5/9. For example, 98.6 °F = (98.6 − 32) × 5/9 = 66.6 × 5/9 = 37 °C. A quick shortcut: subtract 32, then divide by 1.8.

Absolute zero is the lowest theoretically possible temperature — the point at which particles have minimum thermal motion. It equals 0 K = −273.15 °C = −459.67 °F = 0 °R. It cannot be reached in practice, only approached asymptotically.

−40 degrees is the only temperature that is identical on both the Celsius and Fahrenheit scales: −40 °C = −40 °F. You can verify this: −40 × 9/5 + 32 = −72 + 32 = −40.

Kelvin (K) is the SI base unit of thermodynamic temperature. It uses the same interval size as Celsius but starts at absolute zero rather than the freezing point of water. Because it is an absolute scale with a fixed zero point, temperature values in Kelvin are written without a degree symbol (e.g. 300 K, not 300 °K).

Rankine (°R) is an absolute temperature scale that uses Fahrenheit-sized intervals but starts at absolute zero (0 °R = −459.67 °F). It is used in some fields of US engineering thermodynamics, particularly in aerospace and steam-power calculations, where imperial units are preferred but an absolute scale is required.

The Delisle scale (invented 1732) was originally calibrated from the boiling point of water downwards — 0 °De = 100 °C (boiling), and 150 °De = 0 °C (freezing). This inverted convention made sense when the scale was first created using the contraction of mercury in a thermometer, and it was widely used in Russia for much of the 18th century.

Normal human body temperature is approximately 37 °C = 98.6 °F = 310.15 K. Note that 98.6 °F is a commonly cited average; normal body temperature actually varies between individuals (roughly 36.1–37.2 °C / 97–99 °F).