🌡️ Temperature Unit Converter
The Formulas
- °F = (°C × 9 ÷ 5) + 32; °C = (°F − 32) × 5 ÷ 9
- K = °C + 273.15 (no degree symbol, never negative)
Three anchors cover most daily life: 0°C = 32°F (freezing), 37°C = 98.6°F (body temperature), 100°C = 212°F (boiling at sea level).
Why Three Scales Exist at All
- Fahrenheit (1724): Daniel Fahrenheit pinned 0°F to the coldest thing he could reliably make — an ice/salt brine — and ~96°F to body temperature. The odd numbers are historical accident, but the fine granularity (180 steps between freezing and boiling) is why US weather reports still like it.
- Celsius (1742): Anders Celsius used water's freezing and boiling points as 0 and 100 — actually reversed in his original version (100 was freezing!) and flipped after his death.
- Kelvin (1848): Lord Kelvin anchored his scale at absolute zero (−273.15°C), where molecular motion is minimal. Kelvin uses Celsius-sized steps, which is why converting is a simple +273.15.
- The −40 crossover: −40°C = −40°F exactly — solve x = 1.8x + 32 and you get −40. A favorite trivia checkpoint, and genuinely useful in Arctic weather reports.
Oven Settings at a Glance
American recipes bake in Fahrenheit; most ovens elsewhere are marked in Celsius. Rounded values (a degree or two doesn't matter in practice):
| °F (recipe) | 300 | 325 | 350 | 375 | 400 | 425 | 450 |
|---|---|---|---|---|---|---|---|
| °C (oven dial) | 149 | 163 | 177 | 191 | 204 | 218 | 232 |
UK recipes may also cite Gas Marks: Gas Mark 4 = 350°F ≈ 177°C, and each mark step is 25°F.
Frequently Asked Questions
Which countries still use Fahrenheit?
Day-to-day: the United States plus a handful of territories and Belize. Nearly everyone else — including the UK for weather — has gone Celsius, though UK ovens and US science labs freely mix conventions.
Where would I meet Kelvin outside a lab?
Light bulbs and displays: color temperature. A "warm white" bulb is ~3000K, daylight ~5000–5500K, cool white ~6500K — Kelvin describing the color of an ideal glowing body at that temperature.
Is 98.6°F really "normal" body temperature?
It's the classic 37°C converted, from 19th-century data. Modern studies put average adult temperature slightly lower (~36.5°C / 97.7°F) and it varies by person and time of day; fever thresholds (38°C / 100.4°F) are what matter clinically.
Why can't the converter show −300°C?
It can display it, but no such temperature exists — absolute zero is −273.15°C (0 K). Any reading below that indicates a typo, not new physics.