-398 degrees Celsius = -684.4°F (exact). Rounded: -684.4°F. In Kelvin: -124.85 K. In Rankine: -224.73°R.
−40°C = −40°F — the unique point where both scales meet. Found in extreme continental winters.
Below freezing: -398°C = -684.4°F. Key landmarks: 0°C = 32°F (freezing), −10°C = 14°F (cold winter), −20°C = −4°F (severe cold), −40°C = −40°F (where scales meet).
All temperature units: -684.4°F · -124.85 K (Kelvin) · -224.73°R (Rankine). Kelvin starts at absolute zero (−273.15°C). Rankine is used in some US engineering applications.
Formula: °F = (°C × 9/5) + 32. For -398°C: (-398 × 1.8) + 32 = -716.4 + 32 = -684.4°F. Reverse: °C = (°F − 32) × 5/9 = (-684.4 − 32) × 0.5556 = -398°C.
-398°C = -684.4°F (exact: -684.4°F). Formula: (-398 × 9/5) + 32 = -684.4°F.
Multiply by 1.8 then add 32: -398 × 1.8 = -716.4, + 32 = -684.4°F. Quick estimate: double the Celsius value and add 30 → -766°F (approximate).
Add 273.15: -398 + 273.15 = -124.85 K. Kelvin is used in science — 0 K is absolute zero (the coldest possible temperature).
−40°C = −40°F — the unique point where both scales meet. Found in extreme continental winters. In Fahrenheit: -684.4°F is below freezing.