100 C to F

100 degrees Celsius is 212 degrees Fahrenheit

The conversion is exact and short: 100 x 9 / 5 + 32 = 212. One hundred degrees Celsius equals 212 degrees Fahrenheit, and that pair is the boiling point of pure water at one atmosphere of pressure. In kelvin the same temperature is 100 + 273.15 = 373.15 K, and in Rankine it is 373.15 x 9 / 5 = 671.67 R.

Nothing in that arithmetic depends on the weather, the pot or the stove. Celsius and Fahrenheit are two scales pinned to the same physical events, the freezing and boiling of water, and 100 C is one of the two pins. The Fahrenheit scale sets 32 at freezing and 212 at boiling, which is why the two scales share 180 degrees over the same span that Celsius covers in 100.

For a cook, 212 F is the temperature of a rolling boil at sea level, the number behind every boiling water bath canning chart and every pasta pot. For a student, it is the second fixed point of the Celsius scale, and the cleanest example of why the conversion formula works the way it does.

The converter above starts at 100, so the first reading on screen is 212 F. Move the input down to 90 and the answer slides to 194 F, 1.8 degrees for every single Celsius degree.

The formula, worked one step at a time

Two steps, in this order: multiply by 1.8, then add 32. At 100 degrees the multiplication gives 100 x 1.8 = 180, and 180 + 32 = 212 F. Going back, subtract 32 first: 212 - 32 = 180, then 180 x 5 / 9 = 100 C. Order matters, because adding 32 before multiplying turns 212 into 439, a mistake that shows up often in spreadsheet formulas.

The reason for 1.8 is the size of the degree. A Celsius degree is 1.8 times a Fahrenheit degree, so any span of 100 Celsius degrees covers 180 Fahrenheit degrees. The same ratio makes a 5 C day read 41 F and a 10 degree Celsius warm-up equal 18 Fahrenheit degrees.

Around 100 the formula is worth checking against known pairs: 90 C is 194 F, 95 C is 203 F, 99 C is 210.2 F and 101 C is 213.8 F. Each single Celsius degree near boiling moves the Fahrenheit reading 1.8 degrees, which is why a thermometer marked in whole Fahrenheit degrees is coarser than one marked in Celsius.

100 C and 100 F are not the same temperature

This is the mix-up that sends people to a converter in the first place. 100 C is boiling water at 212 F. 100 F is a warm body at 37.78 C, close to a low-grade fever and nowhere near a boil. The two readings look alike and sit 112 Fahrenheit degrees apart.

The arithmetic behind the fever rows: 100 - 32 = 68, and 68 x 5 / 9 = 37.78 C. The fever line converts the same way, 100.4 - 32 = 68.4, then 68.4 x 5 / 9 = 38 C. A thermometer that beeps at 100.4 F is beeping at 38 C, not at 100 C.

Weather adds a third source of confusion. A 100 F afternoon is 37.78 C, the kind of heat Phoenix gets. A 100 C afternoon does not happen on Earth. When a US headline says temperatures hit 100, the scale is Fahrenheit and the story is about heat, not about boiling.

Boiling point at altitude: a pot in Denver never reaches 100 C

Water boils when its vapor pressure matches the air pressure above it, and air pressure falls with elevation. At sea level the match happens at 100 C, or 212 F. In Denver, at about 5,280 feet, the pressure is roughly 12.1 psi instead of 14.7, and water boils near 202 F, which is 94.4 C. No amount of stirring or salting moves the pot back to 100 C.

The rule of thumb is about 1.8 Fahrenheit degrees per 1,000 feet. At 5,000 feet the drop is 5,000 / 1,000 x 1.8 = 9 Fahrenheit degrees, taking 212 down to 203. A candy thermometer or a canning chart calibrated at sea level reads low in the mountains for that reason.

This is why high-altitude baking instructions exist, and why pressure canning times are longer than boiling water bath times. The water is doing the same job at a lower temperature, so food needs more time to reach the same internal heat.

100 C in the kitchen: boiling water bath canning and sterilization

A rolling boil at 212 F is the working temperature of a boiling water bath canner, the standard method for high-acid foods such as fruit, pickles, jams and acidified tomatoes. The USDA canning guidance sets those process times at 212 F for elevations below 1,000 feet and adds minutes as the boiling point falls with altitude. Jars sit under at least an inch of water, and the clock starts only when the pot returns to a full boil.

Boiling water also sterilizes. Glass jars, tongs and lids held in a rolling boil for 10 minutes are considered sanitized for home use, and 100 C is hot enough to kill the molds and yeasts that spoil jam. It is not hot enough to destroy bacterial spores, which is why low-acid foods such as beans, corn and meat require a pressure canner at 240 F or above.

Other kitchen landmarks near 100 C: milk scalds at about 180 F (82 C), a gentle simmer sits between 185 and 205 F, and a full rolling boil is 212 F. Sugar work starts above boiling, with the thread stage near 230 F, so a pot of syrup passes 212 F on its way up and keeps climbing as the water cooks off.

Above 100 C: what pressure does to the boiling point

If 100 C is where water boils at one atmosphere, raising the pressure raises the boiling point. A pressure cooker holds roughly 15 psi above ambient, which pushes the boiling point to about 250 F, or 121 C. That 21 degree jump turns a 90 minute bean cook into 25 minutes, and it is what makes low-acid canning safe.

The relationship is not linear: each pound of pressure buys less temperature than the last, because the vapor pressure curve of water steepens as temperature rises. The first 5 psi adds about 16 Fahrenheit degrees, while the next 5 adds about 11.

Below one atmosphere the same logic runs in reverse, which is the altitude table from the previous section. A vacuum chamber at half an atmosphere boils water near 81 C, and freeze dryers exploit the same physics at far lower pressures.

Kelvin, Rankine and the absolute scales at 100 C

Absolute scales start at absolute zero instead of at the freezing point of water, so they never carry negative numbers. Kelvin keeps the Celsius degree size and shifts the zero: 100 + 273.15 = 373.15 K. Rankine keeps the Fahrenheit degree size: 373.15 x 9 / 5 = 671.67 R, which is also 212 + 459.67.

Kelvin is the scale of physics and chemistry, and 373.15 K is the number that appears in steam tables, engine cycles and lab protocols. Rankine survives in US engineering practice alongside pounds per square inch and British thermal units.

One style note: the unit is the kelvin, written K without a degree sign, per the NIST SI units page. Fahrenheit and Rankine keep their degree symbols. A reading of 373.15 K and 373.15 degrees Kelvin mean the same thing, but the second phrasing is dated.

The double-and-add-30 shortcut and other rounding traps

The mental shortcut doubles Celsius and adds 30: 100 x 2 + 30 = 230. The true answer is 212, so at this temperature the shortcut runs 18 degrees high, an 8.5 percent miss. The shortcut is tuned to mild weather near 10 C, where it is nearly exact, and it drifts at both extremes.

A better mental method for cooking is to remember a few fixed pairs and interpolate between them: 100 C is 212 F, 150 C is 302 F, 180 C is 356 F and 200 C is 392 F. Oven dials in Europe are marked in Celsius and US recipes in Fahrenheit, so those four pairs cover most baking.

Rounding is the other trap. 373.15 K is often printed as 373 K, a 0.04 percent difference that matters only in a lab. 212 F is exact by the definition of the old scale, while the modern ITS-90 realization of the boiling point of water at one atmosphere is 99.974 C. For anything in a kitchen, 100 C and 212 F remain the right pair.