Celsius to Fahrenheit

°F = °C × 9/5 + 32. Multiply the Celsius value by 9, divide by 5 (or just multiply by 1.8), then add 32. To go the other way: °C = (°F − 32) × 5/9. This tool runs both formulas live as you type and also shows the Kelvin equivalent.

The easiest approximation: double the Celsius value and add 30. So 20 °C → 40 + 30 = 70 °F (actual 68 °F). 25 °C → 50 + 30 = 80 °F (actual 77 °F). 30 °C → 60 + 30 = 90 °F (actual 86 °F). It overestimates by a few degrees but is good enough for weather, cooking, and most everyday conversation.

Water freezes at 0 °C / 32 °F and boils at 100 °C / 212 °F (at sea-level atmospheric pressure). Those two reference points are how Anders Celsius originally defined his scale in 1742. Fahrenheit set 32 °F and 212 °F for the same points, which is why the conversion involves both a multiplier and an offset.

Average healthy body temperature is around 37 °C, which is 98.6 °F — the figure most people memorise. Modern research shows the typical range is closer to 36.1–37.2 °C (97.0–99.0 °F) and varies by time of day, age, and how the reading is taken. A fever is generally considered 38 °C / 100.4 °F or higher.

Useful anchors: 0 °C = 32 °F (freezing), 10 °C = 50 °F (cool), 20 °C = 68 °F (mild), 25 °C = 77 °F (warm), 30 °C = 86 °F (hot), 35 °C = 95 °F (very hot), 40 °C = 104 °F (extreme heat). On the Fahrenheit side, 90 °F (32 °C) is a hot summer day in most places, and 100 °F (38 °C) is heat-wave territory.

The Fahrenheit scale (proposed by Daniel Gabriel Fahrenheit in 1724) became the standard across the English-speaking world. Most countries switched to Celsius during the 19th and 20th-century push to metric for consistency with science and trade. The United States is the main holdout for everyday temperature, alongside a handful of others (Belize, the Bahamas, the Cayman Islands, and Liberia). Scientists everywhere — including in the US — use Celsius and Kelvin.

Kelvin is the SI unit of temperature, used in physics and chemistry. It uses the same degree size as Celsius but starts at absolute zero (the theoretical point where all motion stops): 0 K = −273.15 °C = −459.67 °F. To convert: K = °C + 273.15. So 0 °C = 273.15 K, room temperature (20 °C) is 293.15 K, and water boils at 373.15 K. Kelvin is always written without the degree symbol.

It is the one temperature where the two scales cross. The formula °F = °C × 9/5 + 32 has exactly one fixed point. Set °F = °C and solve: C = (C × 9/5) + 32 → −32 = C × 4/5 → C = −40. Above that, Fahrenheit numbers are larger; below it, Celsius numbers are larger (more negative). It is a useful sanity check when working with very cold values.

Yes. For Fahrenheit to Celsius, subtract 30 and halve — gives the same level of approximation in reverse (90 °F → 60 → 30 °C, actual 32.2). For more precision, the exact factor is ×1.8 + 32 either way. If you need full precision (cooking, lab, medical), use the calculator above rather than mental math — the offsets matter for small differences in body or oven temperature.

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