21 degrees Celsius = 69.8°F (exact). Rounded: 69.8°F. In Kelvin: 294.15 K. In Rankine: 529.47°R.
Comfortable warm — typical summer day in Europe and much of the US.
For context: 0°C = 32°F (freezing), 20°C = 68°F (room temp), 37°C = 98.6°F (body temp), 100°C = 212°F (boiling). The Celsius scale places 0° and 100° at the freezing and boiling points of water at sea level.
All temperature units: 69.8°F · 294.15 K (Kelvin) · 529.47°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 21°C: (21 × 1.8) + 32 = 37.8 + 32 = 69.8°F. Reverse: °C = (°F − 32) × 5/9 = (69.8 − 32) × 0.5556 = 21°C.
21°C = 69.8°F (exact: 69.8°F). Formula: (21 × 9/5) + 32 = 69.8°F.
Multiply by 1.8 then add 32: 21 × 1.8 = 37.8, + 32 = 69.8°F. Quick estimate: double the Celsius value and add 30 → 72°F (approximate).
Add 273.15: 21 + 273.15 = 294.15 K. Kelvin is used in science — 0 K is absolute zero (the coldest possible temperature).
Comfortable warm — typical summer day in Europe and much of the US. In Fahrenheit: 69.8°F is warm.