Core answer: °F = °C × 1.8 + 32; °C = (°F − 32) / 1.8. Anchors: water freezes at 0 °C = 32 °F, boils at 100 °C = 212 °F; body temperature 37 °C = 98.6 °F; −40 °C = −40 °F (the crossover). Oven recipes: 180 °C = 356 °F — the most common baking temperature.

The anchor table

°C°FMeaning
−40−40the crossover point
−180freezer
032water freezes
2068room temperature
3798.6body temperature
40104fever threshold (high)
100212water boils (sea level)
180356standard baking
220428high-heat roasting

Mental math shortcuts

  • °C → °F fast: double it, minus 10% of that, add 32. 25 °C → 50 − 5 + 32 = 77 °F ✓
  • °F → °C fast: minus 32, halve, plus 10% of that half. 95 °F → 63/2 = 31.5 + 3 = ~35 °C ✓

Kelvin: the scientist's scale

K = °C + 273.15. Kelvin has no negative values — 0 K is absolute zero, where molecular motion stops. Ratios make sense only in Kelvin: 300 K is "twice as hot" as 150 K in physics terms; 30 °C is NOT twice 15 °C.

Worked examples

Example 1 — US oven recipe. "Bake at 350 °F" → (350 − 32)/1.8 = 176.7 → set your oven to 175–180 °C.

Example 2 — Travel weather. Phoenix at 110 °F: (110 − 32)/1.8 = 43.3 °C — genuinely dangerous heat.

Example 3 — Fever check. A US thermometer reads 100.4 °F: (100.4 − 32)/1.8 = 38.0 °C — yes, that's a fever (≥ 37.3 °C by Chinese standards).

Example 4 — Weather parity day. 16 °C ≈ 61 °F and 28 °C ≈ 82 °F — memorize ±: every 5 °C step is exactly 9 °F.

Common mistakes and myths

  1. Forgetting the +32 — multiplying by 1.8 alone converts *differences*; absolute temperatures need the offset.
  2. Thinking 30 °C is twice 15 °C — temperature ratios are meaningless outside Kelvin.
  3. Body temp drift myth — 37 °C is a rounded 19th-century average; normal range is 36.0–37.2 °C by site (armpit reads ~0.3–0.5 °C lower than oral).
  4. Assuming °F is more precise — the scales are arbitrary; 1 °F steps are just smaller (1 °C = 1.8 °F).
  5. Ignoring altitude in boiling points — water boils at ~93 °C in Lhasa (3,650 m); recipes and sterilization times need adjustment above ~2,000 m.