Temperature Converter
Convert between Celsius, Fahrenheit, and Kelvin in real time. Enter a value in any unit and see all three equivalents instantly. Visual thermometer shows the relative temperature scale.
0°C
Freezing point of water
Common Temperatures
Temperature Converter — Convert °C, °F, K Online Free: Convert temperatures between Celsius, Fahrenheit, and Kelvin instantly. Real-time conversion with visual thermometer. Free online temperature converter.
How to Convert Temperatures
Enter a Value
Type a temperature in any of the three fields — Celsius, Fahrenheit, or Kelvin. The other two fields update instantly.
See All Scales
The visual thermometer and stats bar show the equivalent temperature in all three scales. The color indicates relative hot/cold.
Quick Presets
Click common temperature buttons (freezing, body temp, boiling) to see their equivalents across all three scales instantly.
Understanding Temperature Scales
Temperature measures the average kinetic energy of particles in a substance. Three scales are in common use worldwide, each defined by different reference points and developed for different purposes. Understanding when and why each scale was created helps explain their seemingly arbitrary relationships.
Celsius (°C), also called centigrade, was proposed by Swedish astronomer Anders Celsius in 1742. It's defined by water: 0°C is the freezing point and 100°C is the boiling point at standard atmospheric pressure. This clean 0-100 scale makes Celsius intuitive for everyday weather, cooking, and scientific measurements. It's the standard temperature scale in virtually every country except the United States.
Fahrenheit (°F) was developed by Daniel Gabriel Fahrenheit in 1724. He set 0°F as the temperature of an ice-salt-water mixture (the coldest he could reliably create in a lab), and 96°F as human body temperature (later adjusted to 98.6°F). Water freezes at 32°F and boils at 212°F — a 180-degree range. The U.S. is the only major country still using Fahrenheit for everyday purposes.
Kelvin (K) is the SI base unit for temperature, used in science and engineering. It starts at absolute zero (0 K = -273.15°C), the theoretical point where all molecular motion stops. The Kelvin scale uses the same degree size as Celsius but shifts the zero point. Water freezes at 273.15 K and boils at 373.15 K. Note that Kelvin doesn't use the degree symbol — it's "273 K," not "273°K."
Conversion Formulas
°C → °F
Multiply by 9/5 (or 1.8), then add 32. Formula: °F = (°C × 9/5) + 32. Quick trick: double °C and add 30 for a rough estimate.
°F → °C
Subtract 32, then multiply by 5/9. Formula: °C = (°F − 32) × 5/9. Quick trick: subtract 30, then halve for a rough estimate.
°C → K
Add 273.15. Formula: K = °C + 273.15. The degree size is identical — only the zero point differs between Celsius and Kelvin.
Fun Fact: −40°
−40 is the only temperature where Celsius and Fahrenheit are equal. The formulas intersect at exactly −40. Try it: (−40 × 9/5) + 32 = −40.
Frequently Asked Questions
Absolute zero is 0 Kelvin (−273.15°C / −459.67°F). It's the theoretical lowest temperature possible — the point at which all atomic motion would stop. In practice, absolute zero can never be fully reached, but scientists have cooled matter to within billionths of a degree above it.
Historical inertia. Fahrenheit was the dominant scale when the US was founded. While most countries switched to Celsius through the metric system adoption in the 19th-20th centuries, the US never completed metrification. For weather, Fahrenheit's finer granularity (180 degrees between freezing and boiling vs. 100 in Celsius) can actually be useful — 1°F is a smaller, more perceptible change than 1°C.
The traditional value is 98.6°F (37°C), but modern research shows the average is closer to 97.9°F (36.6°C) and varies throughout the day. Normal ranges are 97–99°F (36.1–37.2°C). A fever is generally defined as 100.4°F (38°C) or higher.
For °C to °F: double the Celsius value and add 30. This gives an approximate Fahrenheit value (within 1-2 degrees for normal weather ranges). Example: 25°C → 25×2+30 = 80°F (actual: 77°F). For °F to °C: subtract 30, then halve. Example: 80°F → (80-30)/2 = 25°C (actual: 26.7°C).