About the Scales
The US reads weather and ovens in Fahrenheit; nearly everyone else lives in Celsius; science runs on Kelvin. Recipes, travel forecasts, medical thermometers, and datasheet specs cross these borders constantly — and the conversion is simple enough that the real skill is sanity-checking the answer against known anchors.
Enter any temperature — negatives included — and get all three scales with the formula worked. The anchors table below is the part worth internalizing; with four or five reference points, most conversions become estimation rather than arithmetic.
Converting oven temperatures while scaling a recipe? Pair this with the Recipe Converter.
The Exact Formulas
The 9⁄5 factor exists because 100 Celsius degrees span the same range as 180 Fahrenheit degrees:
°F = °C × 9⁄5 + 32 °C = (°F − 32) × 5⁄9 K = °C + 273.15 Mental shortcut: °F ≈ °C × 2 + 30 (good within ~4° for weather)
Worked examples: 100 °C = 212 °F (boiling), 98.6 °F = 37 °C (the textbook body temperature), and −40° is the same in both scales — the crossover every physics teacher loves.
Anchor Points Worth Memorizing
Five anchors cover most real-world estimation:
| Reference | °C | °F |
|---|---|---|
| Scales cross | −40 | −40 |
| Water freezes | 0 | 32 |
| Room temperature | 20–22 | 68–72 |
| Body temperature | 37 | 98.6 |
| Hot summer day | 35 | 95 |
| Water boils (sea level) | 100 | 212 |
| Moderate oven | 180 | 356 |
Fever check without math: 38 °C ≈ 100.4 °F is the common clinical fever threshold — a pair worth knowing exactly.
Oven & Weather Quick Sense
Kitchens: UK/EU recipes bake at 160–220 °C, US recipes at 325–425 °F — the ranges map almost perfectly (180 °C ≈ 350 °F is the single most useful pair, the “moderate oven” both traditions share). Fan/convection ovens typically run recipes ~20 °C / 25 °F lower than conventional settings, a conversion layered on top of the scale change.
Weather intuition for travelers: 0 °C is freezing, 10 °C a jacket, 20 °C pleasant, 30 °C hot, 40 °C dangerous — versus 32/50/68/86/104 °F. Kelvin never appears in daily life precisely because its zero is absolute: it exists so equations don't need negative temperatures, not so forecasts can avoid them.