Temperature Converter

Enter a value on either side and Celsius (°C), Fahrenheit (°F) and Kelvin (K) update live. Handy for foreign weather forecasts, US-style oven settings, lab data and physics homework.

From

Live conversion

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Tip: -40 °C and -40 °F are the same temperature; absolute zero = 0 K = -273.15 °C = -459.67 °F.

Formula

°F = °C × 9/5 + 32 K = °C + 273.15 °C = (°F − 32) × 5/9 K = (°F − 32) × 5/9 + 273.15

· Water freezes at 0 °C = 32 °F = 273.15 K (at one standard atmosphere).
· Water boils at 100 °C = 212 °F = 373.15 K.
· Normal human body temperature is about 37 °C ≈ 98.6 °F ≈ 310.15 K.
· −40 °C equals −40 °F — the unique crossover point of the two scales.
· Kelvin is the SI base unit, starting at absolute zero (0 K = −273.15 °C). No degree symbol — write “300 K”, not “300 °K”.
· Reference: NIST SP 811 (2008) §B.8 Temperature conversion.

Frequently asked

Hong Kong uses Celsius — why bother learning Fahrenheit?

The Hong Kong Observatory, news outlets and schools all use Celsius. But Fahrenheit is still everyday in the US — travel weather apps, American ovens and dryers, imported recipes and medical records often use °F. Memorise three anchors: 0 °C = 32 °F (freezing), 100 °C = 212 °F (boiling), body temp 37 °C ≈ 99 °F. Use this tool whenever the numbers don't line up.

When is Kelvin (K) actually useful?

Kelvin is the SI temperature unit, starting at absolute zero (0 K = −273.15 °C) — so it is never negative. It shows up in (1) physics and chemistry equations (PV = nRT requires Kelvin); (2) astronomy of stellar temperatures (the Sun is ~5,778 K); and (3) photography and design colour temperature (candle ~1,800 K, daylight ~5,500 K, cool white ~6,500 K). Rarely needed for everyday life, but unavoidable in DSE physics, chemistry and computer graphics.

Why does −40 °C equal −40 °F?

The two scales have different zero points and step sizes. Solving C = (F − 32) × 5 / 9 = F gives F = −40. Any two non-parallel lines must intersect somewhere, and −40 happens to be where Celsius and Fahrenheit cross. That is why polar weather or a Canadian cold snap reads the same value in both scales.

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