Temperature Converter - Celsius, Fahrenheit, Kelvin

Temperature is the one measurement where most of the world and the United States simply do not speak the same language.

If you grew up with Fahrenheit, a weather forecast of 28 degrees Celsius means nothing until you convert it. If you are accustomed to Celsius, seeing an oven recipe call for 350 degrees Fahrenheit requires a quick calculation before you can preheat. This temperature converter eliminates the guesswork by converting between Celsius, Fahrenheit, and Kelvin instantly.

Unlike length or weight conversions, temperature conversion is not a simple multiplication. The Celsius and Fahrenheit scales have different zero points and different degree sizes, which means the conversion formula involves both multiplication and addition. The Kelvin scale adds another layer because it starts at absolute zero rather than an arbitrary reference point. This tool handles all three scales and shows the exact formula used so you understand the math behind the result.

Whether you are checking international weather forecasts, adjusting cooking temperatures for a European or American recipe, interpreting a medical thermometer reading, or working on a science problem that requires Kelvin, this converter gives you accurate results with a single click.

The Three Temperature Scales

Each of the three major temperature scales was designed with different reference points and use cases in mind.

Celsius (Centigrade). The Celsius scale sets 0 degrees at the freezing point of water and 100 degrees at the boiling point of water, both at standard atmospheric pressure. This makes it intuitive for everyday weather and cooking. The scale was proposed by Anders Celsius in 1742, though his original version was inverted (100 for freezing, 0 for boiling). It was reversed to its current form shortly after. Celsius is the standard temperature unit in every country except the United States, the Bahamas, the Cayman Islands, and Palau.

Fahrenheit. The Fahrenheit scale was developed by Daniel Gabriel Fahrenheit in 1724. It sets 32 degrees as the freezing point of water and 212 degrees as the boiling point, creating a span of 180 degrees between those two reference points. Fahrenheit originally set 0 degrees at the temperature of a brine solution (the coldest he could reliably reproduce in his lab) and 96 degrees at approximately human body temperature. The scale offers finer granularity for weather temperatures, since the range of common outdoor temperatures (roughly 0 to 100 degrees Fahrenheit) spans a wider numeric range than the same span in Celsius (roughly -18 to 38 degrees).

Kelvin. The Kelvin scale is the SI unit of temperature used in science and engineering. It starts at absolute zero, the theoretical temperature where all molecular motion ceases, which equals -273.15 degrees Celsius or -459.67 degrees Fahrenheit. Kelvin uses the same degree size as Celsius, so a temperature change of 1 Kelvin equals a change of 1 degree Celsius. The Kelvin scale has no negative values, which simplifies many physics and chemistry equations. Note that Kelvin temperatures are written without a degree symbol: 300 K, not 300 degrees K.

Celsius to Fahrenheit Formula

The conversion from Celsius to Fahrenheit is the most commonly needed temperature formula.

Formula: F = (C x 9/5) + 32

The 9/5 factor (or 1.8) accounts for the difference in degree size between the two scales. One Celsius degree spans 1.8 Fahrenheit degrees. The addition of 32 accounts for the offset between the two zero points (water freezes at 0 C but 32 F).

Step-by-step example: Convert 25 degrees Celsius to Fahrenheit.

Multiply 25 by 9/5: 25 x 1.8 = 45
Add 32: 45 + 32 = 77
Result: 25 degrees Celsius = 77 degrees Fahrenheit

Common Celsius to Fahrenheit conversions:

-40 C = -40 F (the one point where both scales read the same)
0 C = 32 F (water freezes)
10 C = 50 F (cool day)
20 C = 68 F (comfortable room temperature)
25 C = 77 F (warm day)
30 C = 86 F (hot day)
37 C = 98.6 F (normal body temperature)
100 C = 212 F (water boils)

Fahrenheit to Celsius Formula

Formula: C = (F – 32) x 5/9

Step-by-step example: Convert 72 degrees Fahrenheit to Celsius.

Subtract 32: 72 – 32 = 40
Multiply by 5/9: 40 x 0.5556 = 22.22
Result: 72 degrees Fahrenheit = 22.22 degrees Celsius

Common Fahrenheit to Celsius conversions:

0 F = -17.8 C (very cold winter day)
32 F = 0 C (water freezes)
50 F = 10 C (cool autumn day)
72 F = 22.2 C (room temperature)
98.6 F = 37 C (body temperature)
212 F = 100 C (water boils)
350 F = 176.7 C (common baking temperature)
400 F = 204.4 C (high baking temperature)
450 F = 232.2 C (pizza oven temperature)

Quick Mental Math Tricks

You do not always have access to a converter, so here are reliable mental shortcuts.

Celsius to Fahrenheit shortcut: Double the Celsius temperature and add 30. This gives a rough approximation. For 20 C: double to 40, add 30, get 70 F (actual: 68 F). For 30 C: double to 60, add 30, get 90 F (actual: 86 F). The error increases as you move away from the 5 to 25 C range, but it is close enough for weather estimates.

Fahrenheit to Celsius shortcut: Subtract 30, then divide by 2. For 80 F: subtract 30 to get 50, divide by 2, get 25 C (actual: 26.7 C). Again, this is an approximation that works well in the everyday weather range.

The -40 degree anchor point. Both scales read exactly -40 at the same temperature. This is the only intersection point and can be useful as a mental anchor for extreme cold temperatures.

Kelvin Conversions

Converting to and from Kelvin is simpler than Celsius-Fahrenheit because Kelvin and Celsius share the same degree size.

Celsius to Kelvin: K = C + 273.15 Kelvin to Celsius: C = K – 273.15

Fahrenheit to Kelvin: K = (F – 32) x 5/9 + 273.15 Kelvin to Fahrenheit: F = (K – 273.15) x 9/5 + 32

Important Kelvin reference points:

0 K = -273.15 C = -459.67 F (absolute zero)
77 K = -196 C (boiling point of liquid nitrogen)
273.15 K = 0 C (water freezes)
373.15 K = 100 C (water boils)
5,778 K = approximate surface temperature of the Sun

Kelvin is used in scientific contexts because many physical formulas require an absolute temperature scale. The ideal gas law (PV = nRT), blackbody radiation equations, and thermodynamic calculations all require Kelvin. Using Celsius or Fahrenheit in these formulas produces incorrect results.

Cooking Temperature Conversions

One of the most practical applications of temperature conversion is adjusting recipes between American and international sources.

Oven temperature equivalents:

250 F = 120 C = Gas Mark 1/2 (very slow oven)
300 F = 150 C = Gas Mark 2 (slow oven)
325 F = 163 C = Gas Mark 3 (moderately slow)
350 F = 177 C = Gas Mark 4 (moderate oven)
375 F = 191 C = Gas Mark 5 (moderately hot)
400 F = 204 C = Gas Mark 6 (hot oven)
425 F = 218 C = Gas Mark 7 (hot oven)
450 F = 232 C = Gas Mark 8 (very hot oven)
500 F = 260 C = Gas Mark 10 (extremely hot)

Practical tip: Most ovens are not precisely calibrated, and actual temperature can vary by 10 to 25 degrees from the dial setting. A difference of a few degrees in conversion rounding (e.g., using 175 C instead of 177 C for 350 F) is well within this margin of error and will not affect your results. An oven thermometer is a better investment than worrying about exact conversion precision.

Meat doneness temperatures are commonly referenced in Fahrenheit in American sources:

Rare beef: 125 F (52 C)
Medium-rare beef: 135 F (57 C)
Medium beef: 145 F (63 C)
Well-done beef: 160 F (71 C)
Chicken (safe minimum): 165 F (74 C)

Medical and Scientific Temperature References

Body temperature. Normal human body temperature is often cited as 98.6 F (37 C), but modern research suggests the average is closer to 97.9 F (36.6 C), with a normal range of approximately 97 to 99 F (36.1 to 37.2 C). A fever is generally defined as 100.4 F (38 C) or higher.

Medical thermometers sold in the US typically display Fahrenheit, while those sold internationally display Celsius. Many digital thermometers can switch between both scales. When communicating temperature readings to a healthcare provider in a different country, having the conversion handy avoids miscommunication.

Laboratory and industrial temperatures are typically expressed in Celsius or Kelvin. Liquid nitrogen boils at -196 C (77 K). Dry ice (solid CO2) sublimates at -78.5 C (-109.3 F). Lead melts at 327.5 C (621.5 F). Steel melts at approximately 1,370 to 1,530 C (2,500 to 2,790 F).

The Rankine Scale

A fourth temperature scale, Rankine, is occasionally used in engineering, particularly in the United States for thermodynamic calculations. The Rankine scale is to Fahrenheit what Kelvin is to Celsius: an absolute scale that starts at absolute zero but uses Fahrenheit-sized degrees.

Conversion: R = F + 459.67. Absolute zero is 0 Rankine. Water freezes at 491.67 R. Water boils at 671.67 R.

Rankine appears in some American engineering textbooks and HVAC calculations. This converter supports Rankine for those specialized needs.

Frequently Asked Questions

What is the formula to convert Celsius to Fahrenheit?

The formula is F = (C x 9/5) + 32. Multiply the Celsius temperature by 1.8 (or 9/5), then add 32. For example, 30 C = (30 x 1.8) + 32 = 86 F. For a quick estimate, double the Celsius value and add 30.

What is the formula to convert Fahrenheit to Celsius?

The formula is C = (F – 32) x 5/9. Subtract 32 from the Fahrenheit temperature, then multiply by 0.5556 (or 5/9). For example, 72 F = (72 – 32) x 5/9 = 22.2 C. For a quick estimate, subtract 30 and divide by 2.

What temperature is the same in Celsius and Fahrenheit?

The two scales intersect at exactly -40 degrees. Both -40 C and -40 F represent the same temperature. This is the only point where the two scales are equal.

What is absolute zero?

Absolute zero is 0 Kelvin, which equals -273.15 degrees Celsius or -459.67 degrees Fahrenheit. It is the lowest theoretically possible temperature, where all molecular motion ceases. It has been closely approached in laboratory settings but never actually reached.

What is normal body temperature in Celsius and Fahrenheit?

Normal body temperature is traditionally cited as 98.6 F (37 C), though modern research suggests the average is closer to 97.9 F (36.6 C). A fever is generally considered 100.4 F (38 C) or higher.

What oven temperature is 180 C in Fahrenheit?

180 degrees Celsius equals 356 degrees Fahrenheit. This is close to the common baking temperature of 350 F (177 C). Most recipes calling for 180 C can be set to 350 F with no noticeable difference, since oven calibration varies more than this 6-degree gap.

Why does the US use Fahrenheit instead of Celsius?

The Fahrenheit scale was widely adopted in English-speaking countries before the metric system gained international acceptance. While most countries switched to Celsius during the 20th century, the US retained Fahrenheit for everyday use due to cultural inertia and the costs of transitioning infrastructure. US science uses Celsius and Kelvin.

Conversion formulas based on internationally defined temperature scale relationships. Data accurate as of: March 2026