Convert °C to °F degrees Celsius ↔ degrees Fahrenheit Free Online Secure
Type a temperature in degrees Celsius and read it in degrees Fahrenheit at once. The relation is exact by definition, the arithmetic happens in your browser, and nothing is sent anywhere.
Nothing uploaded
Common values — Convert °C to °F (degrees Celsius ↔ degrees Fahrenheit)
| °C | °F |
|---|---|
| -40 | -40 |
| -10 | 14 |
| 0 | 32 |
| 10 | 50 |
| 20 | 68 |
| 25 | 77 |
| 37 | 98.6 |
| 100 | 212 |
Where these units come from
Fahrenheit set his zero in 1724 at the coldest thing he could make reliably — a brine of ice, water and salt — and put body heat near 96, so that his scale could be divided and divided again. Celsius published his in 1742 the other way up, with 0 for boiling and 100 for freezing; it was turned around after his death, which is why he is remembered for a scale he never used. Kelvin is the only one of the four that begins where there is nothing left to take away: absolute zero. Since 2019 it is defined by fixing the Boltzmann constant rather than by the triple point of water, so the kelvin no longer depends on a particular substance. Rankine is Fahrenheit's degree counted from absolute zero, and Réaumur, with 80 degrees between freezing and boiling, survives mostly in old recipes and in a few cheese dairies.
Where you meet them
Celsius runs weather, cooking and medicine almost everywhere; Fahrenheit does the same work in the United States and keeps a foothold in oven settings and in American recipes. Kelvin belongs to physics, to the colour temperature of lamps and screens, and to anything cold enough that negative numbers would be a nuisance. Rankine appears in American thermodynamics, and Réaumur mainly in historical texts — which is exactly why an old recipe can mislead someone reading it as Celsius.
Questions people ask
Why can't I just double the number to double the temperature?
Because three of these scales have arbitrary zeros. Twenty degrees Celsius is not twice as hot as ten; it is ten degrees further along a scale whose zero was chosen for the convenience of water. Only kelvin and Rankine begin at absolute zero, where there is genuinely nothing left, so only on those two does doubling the figure mean doubling the thermal energy. That is also why every conversion here adds or subtracts as well as multiplying.
Is it true that −40 °C and −40 °F are the same?
Yes, and it is the only place the two scales meet. Fahrenheit degrees are smaller than Celsius ones — nine of them to every five — and the two scales start from different zeros; the one temperature where the difference in size and the difference in starting point cancel out exactly is minus forty. Below that, the Fahrenheit number is the lower of the two.
Is the answer exact?
Where both units are defined in terms of one another by whole numbers, yes — the page says so above the figure, and the only rounding is in how many digits are shown. Where the ratio has no finite decimal, the page shows twelve significant digits and says the relation is approximate rather than pretending otherwise.
Does anything I type leave my device?
No. The arithmetic runs in your browser; nothing is uploaded and there is no server to upload it to. Load the page once and it keeps working with the network switched off.
Weather, fever and the world's extremes: Celsius into Fahrenheit
A forecast in New York says 86 degrees, a thermometer in a Berlin kitchen says 30, and both describe the same warm summer afternoon. Travellers, students, nurses, engineers and anyone who reads an American website meet both scales within a single day. To convert °C to °F, multiply by 9, divide by 5 and add 32: 30 °C is 86 °F, 0 °C is 32 °F and 37 °C is 98.6 °F. The calculator above does the arithmetic as you type, and the sections below show what the figures mean for weather, travel, health, homes and science.
You will find the formula with worked examples, a short profile of each scale, a comparison, a long set of practical cases and the slips to avoid. The arithmetic runs in your browser, and what you type is not sent anywhere.
How to convert °C to °F: multiply by 9/5 and add 32
The formula
The formula is °F = °C × 9/5 + 32, or with decimals °F = °C × 1.8 + 32. So 25 °C gives 25 × 1.8 + 32 = 77 °F, 100 °C gives 212 °F and −10 °C gives 14 °F. To go back, subtract 32 and divide by 1.8.
Worked examples
A mild spring day of 15 °C is 59 °F. A hot day of 35 °C is 95 °F. A freezing night of −5 °C is 23 °F. A fever of 39 °C is 102.2 °F, and boiling water at 100 °C is 212 °F.
Why two steps
The two scales differ in degree size and in their zero points. One Celsius degree is 1.8 Fahrenheit degrees, and water freezes at 0 °C but 32 °F. A conversion therefore needs a multiplication for the size and an addition for the offset.
A quick sanity test
The scales meet at −40, where −40 °C equals −40 °F. If your method gives anything else for −40, a step is wrong.
The Celsius scale
Built on water
The Celsius scale sets 0 at the freezing point of water and 100 at its boiling point at sea-level pressure. It is the everyday scale in almost every country and the base of the kelvin in science.
Where it appears
Weather forecasts, thermostats, medical thermometers and laboratory work.
The Fahrenheit scale
The American scale
On the Fahrenheit scale water freezes at 32 and boils at 212, so 180 degrees separate the two points. It remains the everyday scale in the United States and a few other places, and appears on many American products.
Where it appears
American weather reports, home thermostats, ovens and clinical thermometers.
Celsius against Fahrenheit
From freezing to boiling there are 100 Celsius degrees or 180 Fahrenheit degrees. A Fahrenheit degree is therefore about 0.56 °C, which makes it a finer unit. A change of 10 °C is a change of 18 °F, a point that matters when you read a forecast that says the temperature will fall by so many degrees.
The formula is exact, so rounding only occurs when you display the result. The traps are the order of the operations and the confusion between a temperature and a temperature difference.
Where the conversion shows up
Weather and travel
0 °C is 32 °F, 10 °C is 50 °F, 20 °C is 68 °F, 30 °C is 86 °F and 40 °C is 104 °F. A traveller flying from London in 12 °C to Phoenix in 100 °F lands in a place about 26 °C hotter than home, since 100 °F is 37.8 °C. A quick convert °C to °F before packing avoids a suitcase of the wrong clothes.
Health and the body
Normal body temperature is about 37 °C, or 98.6 °F. A fever starts around 38 °C, which is 100.4 °F. 39 °C is 102.2 °F and 40 °C is 104 °F. Hypothermia begins below 35 °C, or 95 °F. Parents using an American thermometer need a quick convert °C to °F in mind.
Homes and offices
Comfortable room temperature is 20 to 22 °C, which is 68 to 71.6 °F. A thermostat set to 21 °C reads 69.8 °F. Lowering a thermostat by one degree Celsius is often said to save around 6 per cent on heating, which is about 3.3 per cent per Fahrenheit degree, though real savings vary from home to home.
Record temperatures
The lowest air temperature reliably measured on Earth is −89.2 °C, at Vostok Station in Antarctica, which is −128.6 °F. The highest, recorded at Death Valley in 1913, is 56.7 °C, or 134 °F. The range between the two is 145.9 °C, or 262.6 °F. Climate reports quote records in the local scale, so a “convert °C to °F” calculation helps when you compare records across countries.
Data centres
Data centre guidelines recommend an inlet air temperature of 18 to 27 °C, which is 64.4 to 80.6 °F. Each degree above that raises cooling costs and equipment stress. Operators of global facilities keep dashboards in both scales, because engineers from different regions read them.
Wine cellars and aquariums
A wine cellar is best at 12 to 13 °C, or 53.6 to 55.4 °F, with little variation. A tropical aquarium is kept at 24 to 26 °C, or 75.2 to 78.8 °F. A heater with a Fahrenheit dial set to 78 °F gives 25.6 °C, right in the range for most tropical fish.
Gardening and frost
Frost damages tender plants at 0 °C, which is 32 °F. Many seedlings need soil of at least 10 °C, or 50 °F, to germinate. Tomatoes slow down below 13 °C, or 55 °F, and above 32 °C, or 90 °F, their flowers may drop. Seed packets from American suppliers give soil temperature in Fahrenheit, so a “convert °C to °F” calculation on the packet saves seeds.
Construction work
Concrete should not be placed when the air is below 5 °C, which is 41 °F, without cold-weather protection. Paint is usually applied between 10 and 30 °C, or 50 and 86 °F. Adhesives and sealants have similar limits on their labels, often given in both scales, and contractors working with American products check them carefully.
Food storage
Refrigerators should hold 4 °C, which is 39.2 °F, and freezers −18 °C, or −0.4 °F. The danger zone for bacterial growth runs from 5 to 60 °C, or 41 to 140 °F. American food guidance quotes 40 to 140 °F, so the same range appears in two scales.
Heating and hot water
Many American water heaters ship at 120 °F, which is 48.9 °C, to reduce scalding. In Europe 60 °C, or 140 °F, is standard to keep Legionella bacteria under control. At 60 °C a child can be scalded within a few seconds, so mixing valves at taps are an important safety feature.
Altitude and boiling water
Water boils at 100 °C, or 212 °F, at sea level, and about 1 °C lower for each 300 metres of altitude. At 3,000 m it boils near 90 °C, or 194 °F. Mountain cooks adjust times because food cooks more slowly in water that is cooler than 100 °C.
Spreadsheet formulas
Put Celsius values in column A and use =A2*9/5+32 in column B. For the reverse, use =(B2-32)*5/9. For differences, use =A2*9/5 with no offset. Format the result with one decimal, and label the unit in the header so that nobody mistakes a °C column for a °F column.
Rounding and precision
The formula is exact, but real thermometers are not. A household thermometer is good to about one degree. Writing 98.6 °F for 37 °C is correct, while writing 98.60 °F suggests precision that the original reading lacked. Round to the resolution of the instrument.
A mental shortcut
Double the Celsius value and add 30. For 20 °C, that gives 70 °F against an exact 68 °F. For 30 °C, it gives 90 against 86. The method is good within a few degrees for everyday weather but drifts at high or low temperatures, so use the exact formula when it matters.
Absolute zero and the kelvin
Absolute zero is −273.15 °C, which is −459.67 °F. The kelvin scale starts there and uses Celsius-sized steps, so 0 °C is 273.15 K. Scientists seldom use Fahrenheit in the laboratory, but American textbooks may list a freezing point of liquid nitrogen at −320.8 °F, which is −196 °C.
Landmarks to memorise
Four pairs cover much of daily life: 0 °C is 32 °F, 10 °C is 50 °F, 20 °C is 68 °F and 30 °C is 86 °F. Each step of 10 °C adds 18 °F. With these four points you can place any forecast between two known values and judge it by eye.
Reference ladder
−40 °C is −40 °F. −20 °C is −4 °F. 0 °C is 32 °F. 15 °C is 59 °F. 25 °C is 77 °F. 37 °C is 98.6 °F. 50 °C is 122 °F. 100 °C is 212 °F. A ladder like this helps check a figure at a glance.
Checking by reversing
To check any convert °C to °F result, subtract 32 and multiply by 5/9 to see whether you return to the start. If 25 °C became 77 °F, then 77 minus 32 is 45 and 45 times 5/9 is 25. A second test is the direction: above −40, the Fahrenheit value is larger.
Temperature differences
When a forecast says the temperature will rise by 10 degrees, the size depends on the scale: 10 °C is 18 °F. A heating engineer who says the boiler raises water by 20 °C means 36 °F. For differences, only multiply by 1.8, never add 32.
Thermostats and smart homes
Smart thermostats let you switch units, but some store the setting in Fahrenheit internally and round. A target of 21 °C may appear as 70 °F, and then convert back as 21.1 °C. Small rounding like this is harmless, but in a laboratory or a cold storage unit it can matter, so check the scale.
Teaching the scales
Students learn that Anders Celsius chose a scale based on water and that Daniel Fahrenheit built his earlier around brine and body temperature. Comparing the two on a chart shows a straight line crossing at −40. Drawing that line from a few points is a good exercise in linear functions.
Skiing and snow
Ski resorts report snow and air temperature in both scales for international guests. A cold morning of −10 °C is 14 °F, and a spring afternoon of 5 °C is 41 °F. Wax for skis is chosen by snow temperature: a cold wax suits snow below −10 °C, or 14 °F, while a warm wax works near 0 °C, or 32 °F. A quick convert °C to °F before a trip tells you which wax and which layers to pack.
Sleeping and bedroom comfort
Sleep researchers often suggest a bedroom temperature of around 16 to 19 °C, which is 60.8 to 66.2 °F. A room above 24 °C, or 75.2 °F, makes it harder to fall asleep. Sleeping bags carry comfort ratings, for instance 0 °C, or 32 °F, and the American label may show only the Fahrenheit value, so the “convert °C to °F” calculation step helps when you buy abroad.
Airports, flights and cabins
Aircraft cabins are kept near 22 to 24 °C, which is 71.6 to 75.2 °F. Outside at cruising altitude the air is about −55 °C, or −67 °F. Pilots and dispatchers work with both scales, and weather reports for airports carry temperatures in Celsius internationally, but American METARs may differ in format from local forecasts that passengers read.
The Sun and volcanoes
The surface of the Sun is about 5,500 °C, which is 9,932 °F. Lava from basaltic volcanoes flows at 1,000 to 1,200 °C, or 1,832 to 2,192 °F. At such temperatures a difference of 1 °C is 1.8 °F, but the offset of 32 becomes unimportant: 1,100 °C is 2,012 °F, close to double.
Metals and melting points
Lead melts at 327.5 °C, or 621.5 °F. Aluminium melts at 660 °C, or 1,220 °F. Gold melts at 1,064 °C, or 1,947 °F, and iron at 1,538 °C, or 2,800 °F. Blacksmiths and jewellers who work from American books use these figures in Fahrenheit, while their thermocouples may read in Celsius.
Dry ice and liquid nitrogen
Dry ice sublimes at −78.5 °C, which is −109.3 °F, and liquid nitrogen boils at −196 °C, which is −320.8 °F. Both can cause severe burns on contact. Safety notices in the US quote the Fahrenheit values, and a “convert °C to °F” calculation puts them in the same terms as a European data sheet. Handle them with insulated gloves in a ventilated place.
Saunas, spas and pools
A Finnish sauna runs at 80 to 100 °C, which is 176 to 212 °F. A hot tub should never exceed 40 °C, or 104 °F, and many are set at 38 °C, or 100.4 °F. A swimming pool at 26 to 28 °C is 78.8 to 82.4 °F. Seas vary: the Mediterranean in August reaches 25 °C, or 77 °F, and the North Sea stays near 10 °C, or 50 °F.
Running and sport
The best temperature for a marathon is around 10 to 12 °C, which is 50 to 53.6 °F. Performance drops as it rises toward 25 °C, or 77 °F. Race organisers in the US often publish forecasts in Fahrenheit, so runners from Europe convert quickly to decide what to wear and how much to drink.
Cars and engines
An engine coolant runs near 90 °C, which is 194 °F. Asphalt on a sunny day can reach 60 °C, or 140 °F. Tyre pressure rises with temperature: about 1 psi for every 10 °F, or each 5.6 °C. Dashboards in American cars show coolant in Fahrenheit, with the normal range marked around 195 to 220 °F.
Phones and laptops
Phone makers specify an operating range such as 0 to 35 °C, which is 32 to 95 °F. A laptop processor runs near 60 to 80 °C, which is 140 to 176 °F, and throttles above about 95 to 100 °C, or 203 to 212 °F. Leaving a phone on a car seat in summer can exceed these limits, and a “convert °C to °F” calculation shows how quickly.
More values for convert °C to °F
A longer list of conversions
If the value you need is not in the first list, these further conversions may be close enough to read off directly:
- -273.15 °C = -459.67 °F
- -100 °C = -148 °F
- -20 °C = -4 °F
- 10 °C = 50 °F
- 15 °C = 59 °F
- 25 °C = 77 °F
- 30 °C = 86 °F
- 50 °C = 122 °F
Common slips when you convert °C to °F
Forgetting the 32
Multiplying by 1.8 alone gives a figure that is too low. 100 °C is not 180 °F but 212 °F.
Converting a difference as a temperature
A rise of 10 °C is a rise of 18 °F, with no 32 added.
Mixing the scales
Check whether a number on an appliance or label is Celsius or Fahrenheit before you use it.
Short answers
How do I convert °C to °F?
Multiply by 1.8 and add 32.
What is 30 °C in Fahrenheit?
86 °F.
What is 0 °C in Fahrenheit?
32 °F.
When do the scales agree?
At −40.
Does my number leave my device?
No, the calculation runs in your browser.
More pages and a wrap-up
For other temperature conversions see Convert °C to °R, Convert °C to °Ré, Convert °R to °F, Convert °Ré to °F, Convert °F to K, Convert km to mi, Convert mi to km, Convert L to gal, Convert gal to L. The reverse direction is Convert °F to °C.
In short, a “convert °C to °F” calculation means multiplying by 1.8 and adding 32, then writing the unit beside the answer. Your number is computed locally, with no account and no upload.