Celsius to Fahrenheit Converter

Celsius to Fahrenheit — quick reference

The formula, worked line by line

Celsius and Fahrenheit are both linear scales, but they disagree on two things at once: where zero falls, and how large one degree is. Fahrenheit puts the freezing point of water at 32 rather than 0, and it divides the gap between freezing and boiling into 180 steps rather than 100. So the conversion needs a scale factor of 180/100, which reduces to 9/5 or 1.8, and then an offset of 32 to shift the zero into place.

Order matters more than people expect. Multiply first, then add. Adding the 32 before scaling gives an answer that is wrong by 25.6 degrees at every single temperature — (°C + 32) × 1.8 works out to 1.8 × °C + 57.6 instead of 1.8 × °C + 32 — and that one transposition is the most common mistake in hand conversions.

°F = °C × 9/5 + 32
°F = °C × 1.8 + 32
180 °C → 180 × 1.8 = 324, then 324 + 32 = 356.0 °F
For a temperature difference, drop the offset: Δ°F = Δ°C × 1.8

The crossover at minus 40

The two scales cross exactly once. Set the Fahrenheit value equal to the Celsius value and solve: x = 1.8x + 32 gives −0.8x = 32 and x = −40. So −40 °C and −40 °F are the same physical temperature, and feeding −40 into any conversion method is the fastest test that it is set up correctly — a formula with the offset in the wrong place will not return −40.

Two more checkpoints worth memorising are the pair the Celsius scale was built on: 0 °C is 32 °F and 100 °C is 212 °F, water freezing and boiling at sea level. If you need an absolute scale instead, Kelvin shares the size of the Celsius degree, so K = °C + 273.15, while the Fahrenheit-sized absolute scale is Rankine, °R = °F + 459.67.

How to use the celsius to fahrenheit converter

Type a Celsius figure and the Fahrenheit equivalent appears as you type, to one decimal place; Swap turns the page into a Fahrenheit to Celsius converter without retyping the number, which is the fastest way to check an answer in reverse.

Celsius reaches a US reader from a handful of predictable places: the weather app on a trip abroad, a hotel or rental-car thermostat set in metric, a European recipe that gives the oven in degrees C, a thermometer bought overseas, and almost any scientific, industrial or medical figure, since Celsius is the working scale nearly everywhere outside the United States.

The arithmetic here is a multiply and an add rather than a single factor, which is exactly why so many mental conversions come out wrong. The two scales disagree about two things at once: where zero sits, and how big one degree is.

For weather, five anchors do most of the work, and the strip above holds three of them. 10 °C is 50 °F, jacket weather. 30 °C is 86 °F, properly hot. Drop a forecast between two of those and you know what to pack without doing any arithmetic. For the gaps, the rule to hold on to is that every 5 °C is exactly 9 °F, so a five-degree Celsius rise is a nine-degree Fahrenheit rise.

That same ratio explains why Celsius forecasts feel coarse to an American ear: one Celsius degree covers almost two Fahrenheit degrees, so the same weather gets described in fewer, larger steps, and a one-degree change abroad is a bigger deal than it sounds.

Two more places the number has to be right. Food storage: FDA guidance is to keep a refrigerator at 40 °F (4 °C) or below and a freezer at 0 °F (−18 °C), while the UK Food Standards Agency advises a fridge at 5 °C or below, which is 41 °F. Notice that the authorities publish rounded pairs rather than exact conversions, since 0 °F is really −17.8 °C and 40 °F is 4.4 °C.

Body temperature: the NHS treats 38 °C, which is exactly 100.4 °F, as a high temperature, and that is guidance for reading a thermometer rather than medical advice — a reading you are worried about is a reason to call a clinician, not a converter.

Ovens, gas marks and fan settings

Cooking is where the exact figure earns its keep, and where a second layer of convention sits on top of the conversion. British recipes add gas marks, and those are trade conventions rather than exact conversions: Which? publishes gas mark 4 as 180 °C and 350 °F side by side, even though 350 °F is really 176.7 °C.

The reference table above lays out the whole gas ladder from mark 1 to mark 9 so you can move between all three notations in a single look.

Every Celsius value, worked out

71 common Celsius figures each get their own page, with the answer at full precision, the arithmetic, what rounding costs, and the nearest real-world reference point on the scale.

Questions people ask