Celsius to Fahrenheit Converter – Instant, With the Formula

One temperature, two scales

The marker sits on both scales at once. Celsius reads along the top, Fahrenheit along the bottom — watch them disagree everywhere except at one point, -40, where the two scales cross.

Temperatures people actually look up

Weather, bodies and water — the handful of conversions that cover almost every real question.

Oven temperatures, honestly

Recipe books round oven settings to the nearest friendly number. The exact conversion is in the middle column — and at the most-used setting of all, 180 °C, the exact figure is 356 °F, not the 350 °F printed in cookbooks. Both are shown, because your oven dial and the maths are answering slightly different questions.

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Converting in three steps

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Going deeper

Reference table: temperatures you actually meet

The three anchors on this page, 0 °C, 37 °C and 100 °C, cover freezing, body temperature and boiling, but most conversions people look up sit between or beyond them. The table below gives the exact conversions for the temperatures that come up most often, in all three scales, computed from the definitions on this page: Fahrenheit equals Celsius times 9/5 plus 32, and Kelvin equals Celsius plus 273.15. Every figure can be checked by typing the Celsius value into the converter above.

The freezer row is the one that catches people out, because a freezer set to 0 °F is not set to 0 °C, and a freezer set to −18 °C is not set to −18 °F. Zero Fahrenheit is −17.78 °C, so a home freezer at 0 °F runs at about −18 °C, and the two settings that look like they should match differ by eighteen degrees. The same confusion in reverse explains why weather reports from the two systems sound so different: a pleasant 20 °C day is 68 °F, a figure that sounds like a heatwave to someone raised on Celsius and like a mild day to someone raised on Fahrenheit. The table is worth bookmarking for exactly those two cases, the freezer and the weather, where the numbers are familiar in one system and misleading in the other.

Why Fahrenheit’s zero and 100 are odd numbers

Celsius was designed around water: zero where it freezes, one hundred where it boils, at sea level. Fahrenheit was designed around things its inventor could reproduce in a laboratory in the early 1700s, and its landmarks show it. Daniel Fahrenheit set zero at the coldest temperature he could reliably produce, a mixture of ice, water and ammonium chloride, which is a brine that freezes far below pure water. He set the freezing point of pure water at 32, and human body temperature, as he measured it, at 96, giving a scale with 64 divisions between freezing and body temperature, a number chosen partly because it divides neatly by two, four, eight and sixteen. Later, more precise thermometry moved body temperature to 98.6 °F on the scale as it now stands, which is why the scale’s original logic is invisible today: the landmarks were re-anchored to water’s freezing and boiling points, 32 °F and 212 °F, and body temperature drifted to its modern value.

That history explains the two features of Fahrenheit that annoy newcomers most. The first is the offset of 32: it exists because zero was defined by a brine mixture, not by water, so every conversion must shift by 32 before or after scaling. The second is the factor of 9/5: it exists because the interval between water freezing and water boiling contains 180 Fahrenheit degrees but only 100 Celsius degrees, so each Celsius degree is worth 1.8 Fahrenheit degrees. Neither feature is a mistake; both are the fossil record of a scale built before water became the standard. Celsius, adopted later and designed around water from the start, has neither problem, which is why science uses it, and why Kelvin, which keeps the Celsius degree size but moves zero to absolute zero, is the natural extension of it rather than of Fahrenheit.

Cooking conversions, and the mental shortcut’s error

Oven temperatures are the commonest conversion in practice, and they are also where the mental shortcut, double the Celsius and add 30, does the most damage, because ovens run hot enough for its error to matter. The shortcut is exactly right at 10 °C, giving 50 °F, and it stays within about two degrees of the truth at freezing and at room temperature, which is why it survives. At body temperature it is already about five degrees high, giving 104 °F against the exact 98.6 °F, and at oven temperatures it runs away: at 100 °C it gives 230 °F against the exact 212 °F, an error of eighteen degrees, and at 180 °C it gives 390 °F against the exact 356 °F, an error of thirty-four degrees, enough to burn food that should have baked. The error grows because the shortcut’s slope, two, is steeper than the true slope, 1.8, so every degree above 10 °C adds an extra 0.2 degrees of error, and ovens sit far above 10 °C.

Recipe conversions have a second, quieter source of error: rounding. A recipe written for 350 °F converts exactly to 176.67 °C, which no oven dial shows, so cooks round to 175 °C or 180 °C, and the difference between those two roundings is five degrees, larger than most ovens’ thermostat accuracy anyway. The practical rule is to convert exactly, then round to the nearest setting your oven actually offers, and to accept that the rounded figure, not the exact one, is what the food experiences. For baking, where a few degrees change the rise and the crust, use the converter above rather than the shortcut, and check the result against the table in the first section: 180 °C is 356 °F, 200 °C is 392 °F, and 220 °C is 428 °F, all figures worth memorising if you cook from sources in both systems.

Kelvin, absolute zero, and why scientists shift scales

Kelvin keeps the Celsius degree size and moves zero to the coldest possible temperature, absolute zero, which is −273.15 °C and −459.67 °F. The reason scientists prefer it is that temperature differences and temperature ratios behave differently on different scales, and only a scale that starts at absolute zero gives meaningful ratios. A temperature difference is the same size in Celsius and Kelvin, because the two scales share their degree: a rise of 10 °C is a rise of 10 K. But a ratio is not: 20 °C is not twice as hot as 10 °C in any physical sense, because both figures are measured from water’s freezing point, an arbitrary zero. In Kelvin, 293.15 K is the room-temperature figure, 283.15 K is the cool-day figure, and their ratio, 1.035, is a genuine statement about the average kinetic energy of the molecules involved.

Absolute zero itself is a limit rather than a place anyone has reached: cooling approaches it without ever arriving, because removing the last of a system’s thermal energy would require infinite effort, and quantum mechanics leaves a residual zero-point energy even at the limit. For everyday conversion purposes, none of that matters beyond the shift: add 273.15 to go from Celsius to Kelvin, subtract it to go back, and remember that the Fahrenheit equivalent of absolute zero, −459.67 °F, is the coldest figure the Fahrenheit scale can meaningfully express. The converter above shows all three scales together for exactly this reason: Celsius for weather and cooking, Fahrenheit for the same in the United States, and Kelvin for the science that underlies both, with the same physical temperature wearing three different numbers.

Other scales you may meet: Réaumur and Rankine

Celsius, Fahrenheit and Kelvin are the three scales this page converts, but older books, older instruments and some engineering contexts use two more, and knowing their definitions stops a historical temperature from looking like nonsense. The Réaumur scale, used widely in Europe in the eighteenth and nineteenth centuries, sets water freezing at zero and water boiling at 80, so a Réaumur degree is larger than a Celsius degree: one Réaumur degree equals 1.25 Celsius degrees, and the conversion is Celsius equals Réaumur times 1.25. A summer day of 20 degrees Réaumur is therefore 25 °C, which is 77 °F, and a Réaumur thermometer reading 80 at boiling water is simply the same physical point as 100 °C, counted in larger steps. Réaumur survives today mainly in old cookbooks, in some cheese-making and sugar-refining traditions, and in the occasional antique thermometer, where a reading in the twenties means a warm room, not a freezing one.

The Rankine scale is the Fahrenheit analogue of Kelvin: it keeps the Fahrenheit degree size and moves zero to absolute zero, so Rankine equals Fahrenheit plus 459.67. Room temperature at 68 °F is 527.67 degrees Rankine, water freezes at 491.67 degrees Rankine, which is 32 plus 459.67, and water boils at 671.67 degrees Rankine, which is 212 plus 459.67. Rankine appears in older American engineering thermodynamics, particularly in steam and refrigeration work, where absolute temperatures were needed but the Fahrenheit degree was the working unit. Like Kelvin, it makes temperature ratios meaningful: a gas at 527.67 Rankine has about 1.07 times the absolute temperature of the same gas at 491.67 Rankine, the freezing point, a statement that has no equivalent on the Fahrenheit scale itself. If you meet a temperature in Rankine, subtract 459.67 to reach Fahrenheit and then use this page’s conversions; if you meet one in Réaumur, multiply by 1.25 to reach Celsius and proceed from there.

What 0 °F and 100 °F actually feel like

For a reader raised on Celsius, the Fahrenheit landmarks that matter most are not the freezing and boiling points of water but the round numbers of everyday life, and they translate to figures that are easy to misjudge. Zero Fahrenheit is −17.78 °C, because zero minus 32, times five ninths, is −17.78, which is the temperature of a deep winter night in a continental climate, cold enough that exposed skin is at risk within minutes and that a car left outside needs attention to start. One hundred Fahrenheit is 37.78 °C, because 100 minus 32, times five ninths, is 37.78, which is a very hot summer day, slightly above body temperature, and the point at which shade, water and rest stop being comfort and become safety. A forecast of 0 °F and a forecast of 100 °F are therefore both warnings, at opposite ends of the scale, and both are figures worth recognising without converting, because by the time the conversion is done the clothing decision has already been made.

Between those extremes, the Fahrenheit numbers Americans quote for weather cluster in a range that maps awkwardly onto Celsius: 50 °F is 10 °C, 60 °F is 15.56 °C, 70 °F is 21.11 °C, 80 °F is 26.67 °C, and 90 °F is 32.22 °C. The awkward decimals are the reason weather converters exist at all: unlike the Celsius anchors, which land on round numbers in their own system, Fahrenheit weather figures land on repeating decimals in Celsius, and the table in the first section of this guide is the quickest way through them. The practical rule for travellers is to learn five pairs, 32 and 0, 50 and 10, 68 and 20, 86 and 30, 212 and 100, and to interpolate between them, rather than converting every forecast exactly, because weather is itself an approximation, and a forecast converted to a tenth of a degree is no more accurate than one converted to the nearest whole degree.

Frequently asked questions

Related guides

The full reference chart, from this page’s own guide.

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