Temperature Converter: Celsius, Fahrenheit, Kelvin
Convert between Celsius, Fahrenheit, and Kelvin instantly. Includes formulas, quick reference tables, and visual comparison charts. Explore all measurement categories at our Unit Converter, or calculate annual energy expenses with the Heating Cost Calculator.
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Quick Reference Table
Complete Conversion Reference
Unit Definitions
How it works
Unlike length or weight, temperature conversions are non-linear. Each scale has a different zero point and step size: Celsius sets 0 at water's freezing point, Fahrenheit sets 32 there, and Kelvin starts at absolute zero (−273.15 °C). This means conversion requires both scaling and an offset — not a simple multiplication.
The key formulas are: °F = °C × 9/5 + 32, °C = (°F − 32) × 5/9, and K = °C + 273.15. Enter a value in either field and the converter instantly calculates the result. Use the swap button to reverse direction. The quick reference table covers everyday temperatures from −40 to 100 °C.
How Temperature Conversion Works
Unlike most unit conversions that use simple multiplication, temperature conversion involves both multiplication and addition because Celsius, Fahrenheit, and Kelvin scales have different zero points and step sizes. The formulas are: Fahrenheit = Celsius x 9/5 + 32, Celsius = (Fahrenheit - 32) x 5/9, and Kelvin = Celsius + 273.15. The Fahrenheit degree is smaller than the Celsius degree (a 1 degree C change equals a 1.8 degree F change), and the scales intersect at -40, where -40 C equals exactly -40 F.
Common Temperature Conversions
The most searched temperature conversions involve weather (Celsius to Fahrenheit for travel), cooking (oven temperatures between C and F), body temperature (37 C = 98.6 F), and science (Celsius to Kelvin). Key reference points that people frequently look up: water freezes at 0 C (32 F) and boils at 100 C (212 F). Room temperature is approximately 20-22 C (68-72 F). A fever in adults begins at 38 C (100.4 F). Common oven temperatures range from 150 C (300 F) for slow cooking to 230 C (450 F) for pizza and bread.
When You Need Temperature Conversion
Temperature conversion is needed when following recipes from other countries (American recipes use Fahrenheit, European ones use Celsius), checking weather forecasts while traveling, understanding medical information across systems, and working in science or engineering where Kelvin is standard. HVAC professionals convert between systems when working with international equipment specifications. Travelers from the US visiting Europe need Celsius for weather, while Europeans visiting the US encounter Fahrenheit on thermostats, weather apps, and oven dials.
Temperature Scales Explained
Celsius (centigrade) sets 0 at the freezing point of water and 100 at its boiling point at standard atmospheric pressure. It is used by most countries worldwide. Fahrenheit sets 32 as the freezing point of water and 212 as the boiling point, creating a 180-degree range. Only the United States, its territories, and a few Caribbean nations use Fahrenheit as the primary scale. Kelvin is the SI unit for thermodynamic temperature, starting at absolute zero (-273.15 C), where all molecular motion stops. Each Kelvin step equals one Celsius degree, making conversions straightforward.
Tips for Accurate Temperature Conversion
Memorize a few key reference points rather than calculating every time: 0 C = 32 F, 100 C = 212 F, 37 C = 98.6 F, and the crossover point -40. For quick mental math from Celsius to Fahrenheit, double the Celsius value and add 30 — this gives an approximation within a few degrees for everyday temperatures. For cooking, note that many oven temperatures come in round numbers in one system but not the other: 180 C is 356 F (typically rounded to 350 F), and 400 F is 204.4 C (rounded to 200 C).
Practical Examples
A summer day at 30 C equals 86 F. A cold winter morning at -10 C is 14 F. A medium-rare steak reaches an internal temperature of 57 C (135 F). Liquid nitrogen boils at -196 C (-320.8 F, 77.15 K). The surface of the Sun is approximately 5,500 C (9,932 F, 5,773 K). Normal human body temperature of 37 C is 98.6 F or 310.15 K. A comfortable pool temperature is 26-28 C (79-82 F).
FAQ
- How do I convert Celsius to Fahrenheit?
- Multiply the Celsius value by 9/5 (or 1.8) and then add 32. The formula is: F = C x 9/5 + 32. For example, 25 C x 1.8 + 32 = 77 F. For a quick mental estimate, double the Celsius value and add 30 — this is accurate within a few degrees for everyday temperatures (e.g., 20 C becomes about 70 F instead of the exact 68 F).
- How do I convert Fahrenheit to Celsius?
- Subtract 32 from the Fahrenheit value, then multiply by 5/9 (or divide by 1.8). The formula is: C = (F - 32) x 5/9. For example, 98.6 F: subtract 32 = 66.6, multiply by 5/9 = 37 C. This is the normal human body temperature. For quick mental math, subtract 30 and divide by 2 — approximate but useful for daily weather.
- What is the formula for Celsius to Kelvin?
- Add 273.15 to the Celsius value to get Kelvin. The formula is: K = C + 273.15. For example, 100 C + 273.15 = 373.15 K (boiling point of water). One Kelvin step is the same size as one Celsius degree, so only the zero point differs. Kelvin starts at absolute zero (-273.15 C), the theoretically lowest possible temperature.
- What temperature is the same in Celsius and Fahrenheit?
- Celsius and Fahrenheit are equal at exactly -40 degrees. At -40 C = -40 F, both scales intersect. You can verify this with the formula: F = -40 x 1.8 + 32 = -72 + 32 = -40. This is the only point where the two scales give the same numerical reading. It corresponds to 233.15 Kelvin.
- What is normal body temperature in Celsius, Fahrenheit, and Kelvin?
- Normal human body temperature is approximately 37 C, 98.6 F, or 310.15 K. A fever is typically defined as a temperature above 38 C (100.4 F). The 98.6 F figure comes from a 19th-century German study that measured 36.6 C, which was converted to 98.6 F. Modern research suggests average body temperature may be slightly lower, around 36.6-37 C (97.9-98.6 F).
- How do I convert oven temperatures between Celsius and Fahrenheit?
- Common oven conversions: 150 C = 302 F (slow/low), 180 C = 356 F (moderate, often rounded to 350 F), 200 C = 392 F (moderately hot, rounded to 400 F), 220 C = 428 F (hot), and 250 C = 482 F (very hot). Gas mark equivalents: Gas 4 = 180 C = 350 F, Gas 6 = 200 C = 400 F, Gas 8 = 230 C = 450 F. Always round to the nearest standard setting on your oven.
- What is absolute zero and why does it matter?
- Absolute zero is 0 Kelvin, -273.15 C, or -459.67 F. It is the theoretical lowest temperature where all atomic and molecular motion stops. No object has ever been cooled to exactly absolute zero, though scientists have reached within fractions of a Kelvin. The Kelvin scale starts at this point, making it useful in physics because there are no negative Kelvin temperatures.
- Which countries still use Fahrenheit?
- The United States, its territories (Puerto Rico, US Virgin Islands, Guam), and a few Caribbean nations (Bahamas, Belize, Cayman Islands) use Fahrenheit as their primary temperature scale. Every other country uses Celsius for weather, cooking, and daily life. The UK officially uses Celsius but many people still reference Fahrenheit informally, especially for summer temperatures and body temperature.
- How do I convert cooking temperatures for meat doneness?
- Internal meat temperatures for doneness: Rare = 49-52 C (120-125 F), Medium-rare = 54-57 C (130-135 F), Medium = 60-63 C (140-145 F), Medium-well = 66-68 C (150-155 F), Well-done = 71+ C (160+ F). Poultry must reach 74 C (165 F) for food safety. These are internal temperatures measured with a meat thermometer, not oven settings.
- What is the Kelvin scale used for?
- The Kelvin scale is the SI unit for temperature and is used in all branches of science, engineering, and technology. It is essential in thermodynamics, physics, chemistry, and astronomy. Color temperature of light is measured in Kelvin: daylight is about 5,500-6,500 K, warm incandescent light is about 2,700 K, and candlelight is roughly 1,800 K. Kelvin has no degree symbol — write "300 K" not "300 degrees K."
- What are common weather temperature conversions?
- Key weather reference points: -18 C = 0 F (very cold), 0 C = 32 F (freezing), 10 C = 50 F (cool), 20 C = 68 F (comfortable), 25 C = 77 F (warm), 30 C = 86 F (hot), 35 C = 95 F (very hot), 40 C = 104 F (extreme heat). Each 5 C increment equals 9 F. Memorizing a few of these makes it easy to estimate conversions while traveling.
- How does wind chill affect perceived temperature?
- Wind chill describes how cold air feels on exposed skin when wind is factored in. It is not a direct temperature conversion but a calculated index. For example, an air temperature of -10 C (14 F) with a 30 km/h wind has a wind chill of about -20 C (-4 F). Wind chill is always expressed in the same unit as the base temperature — it does not convert between Celsius and Fahrenheit.
- What is the heat index and how is it calculated?
- The heat index (or "feels like" temperature) combines air temperature and relative humidity to indicate how hot it actually feels. At 33 C (91 F) with 60 percent humidity, the heat index is about 40 C (104 F). Heat index is relevant above approximately 27 C (80 F). Like wind chill, it is expressed in the same unit system as the base temperature, not as a conversion between scales.
- What is the Rankine scale?
- The Rankine scale is the Fahrenheit equivalent of Kelvin — it starts at absolute zero but uses Fahrenheit-sized degrees. The formula is: R = F + 459.67. Water freezes at 491.67 R and boils at 671.67 R. Rankine is used in some US engineering applications, particularly in thermodynamics and the aerospace industry, but is rare outside the US. Most scientific work uses Kelvin instead.
- Why does temperature conversion use addition, not just multiplication?
- Temperature scales have different zero points and different step sizes. Celsius sets 0 at the freezing point of water, while Fahrenheit sets 32 there. This offset means you must add or subtract a constant, not just multiply. Additionally, Fahrenheit degrees are smaller than Celsius degrees (180 F degrees span the same range as 100 C degrees), requiring a 9/5 scaling factor. Together, these create the formula F = C x 9/5 + 32.