Fahrenheit to Celsius Converter
Convert °F to °C and Celsius to Fahrenheit instantly — weather, oven and body temperatures with common reference points.
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How It's Calculated
Unlike most unit conversions, Fahrenheit and Celsius are not related by a simple multiplier — the relationship is an offset-and-scale formula, because the two scales place their zero points in different spots: °C = (°F − 32) × 5⁄9 and °F = °C × 9⁄5 + 32. You always subtract or add 32 first, then apply the 5/9 or 9/5 ratio — skipping the offset and only scaling gives a wrong answer.
Worked example: convert 98.6°F (normal body temperature) to Celsius. Subtract 32: 98.6 − 32 = 66.6. Multiply by 5⁄9: 66.6 × 5⁄9 = 37.0°C. Going the other way, convert 20°C to Fahrenheit: multiply by 9⁄5 first (20 × 9⁄5 = 36), then add 32 (36 + 32 = 68°F, a comfortable room temperature). A handful of anchor points make mental estimates easy without doing the math: water freezes at 32°F/0°C and boils at 212°F/100°C; −40° is the one temperature where both scales agree exactly.
What to Know
- Fahrenheit's original reference points weren't water. Daniel Fahrenheit defined his scale in 1724 using a brine (ice-salt) mixture for 0°F — the coldest stable temperature he could reliably reproduce in his lab — and human body temperature for the upper anchor, originally set near 96°F and later refined to 98.6°F as thermometry improved.
- Absolute zero is the same physical point on every scale. −273.15°C = −459.67°F = 0 Kelvin. Kelvin uses the same step size as Celsius but starts counting from absolute zero instead of the water freezing point, which is why science generally prefers it over Celsius for calculations.
- A common mistake is applying only the 5/9 or 9/5 ratio and forgetting the 32-degree offset — this works by coincidence near 0, but produces increasingly wrong results the further the temperature is from freezing.
- The US, its territories and a handful of other regions use Fahrenheit for everyday weather and cooking; nearly everywhere else, and all of science, uses Celsius.
- Because a Fahrenheit degree is a smaller step than a Celsius degree (9 Fahrenheit degrees span the same range as 5 Celsius degrees), Fahrenheit readings change by a larger number for the same physical temperature swing — one reason US weather forecasts can feel more granular day to day than Celsius ones.
Frequently Asked Questions
What is 350°F in Celsius (oven temperature)?
350°F ≈ 177°C — the standard "moderate oven". Other common settings: 325°F = 163°C, 375°F = 191°C, 400°F = 204°C, 425°F = 218°C.
Is 100°F a fever?
100°F equals 37.8°C — a low-grade fever by most definitions (fever is commonly ≥100.4°F / 38°C). Normal body temperature is around 98.6°F / 37°C.
Why isn't the Fahrenheit-Celsius conversion just a multiplication?
Because the two scales don't share a zero point. Celsius sets 0° at water's freezing point; Fahrenheit sets 0° at a brine mixture's freezing point, roughly 32 Fahrenheit degrees colder. That offset has to be added or subtracted before scaling by 5/9 or 9/5 — it is a linear equation (y = mx + b), not a pure ratio.
What was Fahrenheit's original 0° and 100° based on?
Daniel Fahrenheit, working in 1724, anchored 0°F to the coldest temperature he could stably produce — a mixture of ice, water and ammonium chloride (or salt) — and set his upper reference near human body temperature, originally about 96°F. Later, more precise thermometry moved the accepted body-temperature value to 98.6°F without redefining the scale itself.
Do Celsius and Fahrenheit ever show the same number?
Yes, at −40° — solving °F = °C for the crossing point gives exactly −40°F = −40°C, the only temperature where the two scales agree. This is also the only point where the offset and scale factor cancel out exactly.
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