Temperature Converter

This temperature converter has four modes:

• Quick Convert – Pick your units, type a value, and hit Convert. The swap button flips your "from" and "to" units.
• All Scales – Shows your temperature in all eight scales at once. Turn on historical scales if you need Rankine, Réaumur, and others.
• Cooking Reference – Oven temps and food safety temperatures.
• Body Temperature – Enter a reading and see if it's normal, a fever, or something that needs attention.

The preset buttons at the top give you quick access to temperatures you'll use often—freezing, boiling, body temp, and absolute zero. Click any preset to fill in the value automatically.

Swedish astronomer Anders Celsius created his temperature scale in 1742, originally calling it centigrade. He designed it around the physical properties of water, with freezing at one end and boiling at the other, putting a hundred degrees between them. These are reference points that are easy to recreate. Celsius actually proposed the scale in reverse, with 100 degrees at the freezing point and 0 at boiling, but this was later inverted to the form we use now.

The term centigrade comes from the Latin words centum meaning hundred and gradus meaning step or degree. The scale was officially renamed to Celsius in 1948 to honor its creator and to avoid confusion with an angle measurement term used in some countries.

Daniel Gabriel Fahrenheit, a German physicist, developed his temperature scale in 1724, making it one of the earliest standardized temperature measurement systems. He chose his reference points differently from Celsius, using a salt-ice-water mixture for 0 degrees and body temperature for his upper mark, which he originally set at 96 degrees. Water's freezing point ended up at 32°F and boiling at 212°F, creating a span of 180 degrees between these points.

The Fahrenheit scale remains the primary temperature measurement system in the United States, as well as in a few other territories including the Bahamas, Belize, and the Cayman Islands. Fahrenheit sticks around in American daily life because it works well for weather—the 0 to 100 range covers most weather temperatures people actually deal with, with 0°F representing very cold weather and 100°F representing very hot weather. The smaller degree size also provides slightly more precision without requiring decimal places in everyday use. Old habits die hard.

William Thomson, 1st Baron Kelvin, took a different approach in 1848. Rather than using arbitrary reference points like the freezing of water, Kelvin based his scale on absolute zero—the temperature where molecules stop moving and matter has no heat energy left. This makes Kelvin an absolute thermodynamic temperature scale, needed for scientific calculations where ratios matter. Kelvin uses the same degree increment as Celsius, so a temperature change of one Kelvin equals a change of one degree Celsius—the only difference is the zero point: 0 K equals -273.15°C. This makes converting between them simple. Kelvin is the SI base unit for temperature and is used throughout physics, chemistry, and astronomy. Unlike Celsius and Fahrenheit, Kelvin temperatures are stated without the degree symbol—we write 300 K, not 300°K—because Kelvin is a unit in its own right.

Celsius and Fahrenheit differ in two ways: the scales have different zero points, and they use different-sized degrees. Water freezes at 0°C but at 32°F, creating a 32-degree offset. The 100 degrees between freezing and boiling in Celsius corresponds to 180 degrees in Fahrenheit, giving a ratio of 9 to 5 (or 1.8). The conversion formulas account for both of these differences.

Celsius to Fahrenheit:

1. Multiply by 9/5 (or 1.8)
2. Add 32

Fahrenheit to Celsius:

1. Subtract 32
2. Multiply by 5/9

A common mistake is doing these steps in the wrong order—remember to handle the offset at the right step for each direction.

Absolute zero represents the lowest limit of the thermodynamic temperature scale, the point at which particles have minimal vibrational motion and a system is in its lowest possible energy state. At absolute zero, which occurs at 0 Kelvin, -273.15°C, or -459.67°F, classical physics predicts that all molecular motion would cease entirely. Quantum mechanics shows it's more complicated than that—particles retain zero-point energy even at absolute zero, but no temperature below this point is possible to reach or even define.

Reaching absolute zero would take an infinite number of steps, according to the Third Law of Thermodynamics—so it's practically impossible. Scientists have gotten extremely close, achieving temperatures within billionths of a degree of absolute zero using techniques like laser cooling and magnetic evaporative cooling. At these extreme temperatures, matter does strange things—superfluids and superconductors only exist at these temperatures. We can get close, but never all the way there.

Getting the temperature right makes or breaks your cooking, affecting everything from food safety to the chemical reactions that create flavor and texture. Different cuisines and recipe traditions use different temperature scales, so you need to convert when following recipes from other countries. European recipes typically use Celsius, American recipes use Fahrenheit, and some British recipes still reference the old Gas Mark system. Understanding these conversions prevents the common mistake of setting an oven to 180 when the recipe means 180°C (350°F), not 180°F (which would be too cool for most baking).

Food safety relies heavily on reaching specific internal temperatures to kill harmful bacteria. Poultry must reach 74°C (165°F), ground meats need 71°C (160°F), and whole cuts of beef and pork are safe at 63°C (145°F). Candy making needs exact temperatures at each sugar stage—thread stage is 110°C, hard crack is 150°C. The Maillard reaction, responsible for browning and flavor development in seared meats and baked goods, occurs most effectively between 140°C and 165°C. Understanding these temperature thresholds takes the guesswork out of cooking.

The traditional normal body temperature of 98.6°F (37°C), established by German physician Carl Reinhold August Wunderlich in 1851, has been updated by newer research. Studies now show the average human body temperature is closer to 97.9°F (36.6°C), and normal temperatures can range from 97°F to 99°F (36.1°C to 37.2°C) depending on the individual, time of day, activity level, and measurement method. Body temperature naturally fluctuates, running lower in the morning and higher in the late afternoon.

Fever, defined as an elevated body temperature, serves as an immune response to infection. Low-grade fevers (99.1°F to 100.4°F or 37.3°C to 38°C) often require only rest and fluids, while high fevers above 103°F (39.4°C) warrant medical attention, especially in children and elderly individuals. Hypothermia occurs when core body temperature drops below 95°F (35°C), causing shivering, confusion, and dangerous heart problems. The measurement method affects readings: rectal temperatures run about 0.5-1°F higher than oral readings, while armpit measurements typically read 0.5-1°F lower.

Weather temperatures affect daily life in obvious ways, from clothing choices to health risks. Understanding temperature scales helps when traveling between regions that use different systems. A pleasant 20°C day translates to 68°F, while 30°C represents a hot 86°F. Freezing weather at 0°C corresponds to 32°F, and extreme cold at -20°C means a dangerous -4°F. These benchmarks help travelers and weather watchers interpret reports from any part of the world.

Apparent temperature, or "feels like" temperature, accounts for factors beyond air temperature. Wind chill makes cold air feel colder by accelerating heat loss from exposed skin—a temperature of 0°F with 15 mph wind feels like -19°F. On the flip side, the heat index combines temperature and humidity to express how hot weather actually feels. A 90°F day with 65% humidity can feel like 103°F because high humidity prevents sweat from evaporating effectively. These numbers are more useful for planning outdoor activities and help prevent hypothermia and heat-related illnesses.

Before Celsius and Fahrenheit took over, scientists came up with several other temperature scales. Scottish engineer William Rankine created his scale in 1859 as the Fahrenheit equivalent of Kelvin—an absolute scale starting at absolute zero but using Fahrenheit-sized degrees. Rankine remains used in some American engineering applications, particularly in thermodynamics calculations.

René Antoine Ferchault de Réaumur, a French scientist, introduced his scale in 1730 with freezing at 0 and boiling at 80 degrees. It was widely used in parts of Europe until the mid-20th century. French astronomer Joseph-Nicolas Delisle came up with something different in 1732—a scale that works backward: 0 degrees marks boiling water, and higher numbers indicate colder temperatures, with freezing at 150 degrees.

Scientific work requires temperature measurements in absolute scales, primarily Kelvin. The ideal gas law (PV = nRT) requires temperature in Kelvin to produce meaningful results—using Celsius or Fahrenheit would give nonsensical negative volumes or pressures. Chemical reaction rates double approximately every 10 Kelvin increase—this applies to cooking just as much as factories.

Color temperature, measured in Kelvin, describes what color light looks like based on how hot an object would need to be to glow that color. A standard incandescent bulb emits light at approximately 2700 K, appearing warm and yellowish, while daylight measures around 5500-6500 K with a bluer, cooler appearance. This matters for photography, video, and display calibration.

Star types match up with surface temperature. Red dwarfs run around 3000 K, our Sun hits 5778 K, and blue giants go past 30,000 K.

The most common mistake is doing the formula steps in the wrong order. When converting Celsius to Fahrenheit, you must multiply by 9/5 before adding 32; reversing this order produces incorrect results. For Fahrenheit to Celsius, subtract 32 first, then multiply by 5/9. Another common mistake is confusing which conversion factor to use—remember that Celsius to Fahrenheit uses 9/5 (expanding the scale), while Fahrenheit to Celsius uses 5/9 (contracting it).

Some errors involve impossible temperatures. Kelvin and Rankine cannot have negative values because they are absolute scales with zero at absolute zero—any negative Kelvin value represents a physically impossible temperature. Rounding too early in multi-step calculations compounds errors; keep all the decimals until the end, then round. When converting temperatures for cooking, be especially careful to verify which scale a recipe uses, as confusing 180°F and 180°C gives you completely different results—lukewarm food vs. actually cooked food.