Temperature Converter

The conversion formulas

Temperature scales differ in both the size of a degree and where zero sits, so converting needs a multiplication and an offset. The converter first turns the input into Celsius, then turns Celsius into the target scale:

°C = (°F − 32) × 5/9  ·  °F = °C × 9/5 + 32
K = °C + 273.15  ·  °R = (°C + 273.15) × 9/5 = °F + 459.67

A Celsius degree and a kelvin are the same size; a Fahrenheit degree and a Rankine degree are both 5/9 of that. Kelvin and Rankine start at absolute zero, the lowest possible temperature, so they never go negative.

Worked examples

Example 1: an oven at 350 °F

(350 − 32) × 5/9 = 318 × 5/9 = 176.67 °C. Recipes often round this to 180 °C, or 160 °C for a fan oven.

Example 2: room temperature in kelvin

20 °C + 273.15 = 293.15 K. In Fahrenheit, 20 × 9/5 + 32 = 68 °F.

Example 3: liquid nitrogen

Nitrogen boils at about 77 K at sea-level pressure. 77 − 273.15 = −196.15 °C, which is −321.07 °F.

Example 4: the scales meet

Set °F equal to °C in the formula and solve: x = x × 9/5 + 32 gives x = −40. So −40 °F is exactly −40 °C.

How to read the result

The large figure is the temperature in the scale you picked as the target. The thermometer bar runs from −40 °C to 120 °C and marks where water freezes, normal body temperature and where water boils at sea level, with a dark line at your value; anything outside that range sits at the end of the bar. The table repeats the value in Celsius, Fahrenheit, Kelvin and Rankine, rounded to four decimal places.

Converting differences, not readings

A change of temperature converts without the offset. A rise of 10 °C is a rise of 18 °F, not 50 °F, because only the degree size differs. If a forecast says it will be 5 °C warmer tomorrow, that is 9 °F warmer. Using the reading formula on a difference is a common mistake in science homework and in comparing climate figures; multiply or divide by 1.8 instead.

A short history of the scales

Daniel Gabriel Fahrenheit proposed his scale in 1724, and Anders Celsius his in 1742 (originally with 0 for boiling and 100 for freezing, inverted soon after). Lord Kelvin described an absolute scale in 1848, and William Rankine proposed the Fahrenheit-sized equivalent in 1859. Since 2019 the kelvin has been defined by fixing the value of the Boltzmann constant, and the Celsius scale is defined from the kelvin, which is why 0 °C is exactly 273.15 K.

Common uses

Cooks convert oven settings between American and European recipes; travellers translate weather forecasts; parents check a child's temperature reading from a thermometer set to the other scale; students convert between Celsius and kelvin in chemistry and physics; and engineers working with US thermodynamic tables meet Rankine. Aquarium, brewing and gardening guides frequently quote ideal temperatures in only one scale. For the single most searched direction, the Fahrenheit to Celsius converter adds a mental-math shortcut and a printable table.

Limits and good practice

The converter accepts any temperature at or above absolute zero (0 K, −273.15 °C, −459.67 °F). Below that it shows an error, because such temperatures do not exist in the ordinary thermodynamic sense. Household thermometers are usually accurate to a few tenths of a degree, so round the answer accordingly. A fever threshold or a food-safety temperature should come from a medical or food-safety authority in the scale you use, rather than from a rounded conversion. For other measurements, see the length converter and the weight converter.

Reference temperatures worth remembering

A few anchor points make conversions easy to sanity-check. Water freezes at 0 °C (32 °F, 273.15 K) and boils at 100 °C (212 °F) at standard sea-level pressure; at altitude it boils lower, around 95 °C in Denver at about 1,600 m. A comfortable room is 20–22 °C, or 68–72 °F. Hot tap water is commonly set near 50–60 °C (122–140 °F). A moderate oven runs 180 °C (356 °F) and a hot one 220 °C (428 °F). On the cold side, a typical home freezer is −18 °C, which is almost exactly 0 °F, a handy coincidence. If a converted figure lands far from these anchors for an everyday task, check whether the input scale was picked correctly.