Temperature Converter Online Free — Celsius, Fahrenheit, Kelvin, Rankine and Réaumur

Instantly convert between temperature scales: Celsius, Fahrenheit, Kelvin, Rankine and Réaumur. Conversion formulas with examples, reference values and a complete temperature scale guide for everyday use, medicine and science

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Formula: °C = (°F − 32) × 5/9 · K = °C + 273.15 · −40 °F = −40 °C
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Temperature Reference Values
Absolute Zero (−273.15 °C)

The lowest possible temperature in the universe — the point at which molecular motion theoretically ceases. 0 K = −273.15 °C = −459.67 °F. Serves as the zero point of the Kelvin and Rankine scales. Physically unachievable in practice

Record Cold on Earth (−89.2 °C)

The lowest natural temperature ever recorded on Earth: −89.2 °C (−128.6 °F) at Vostok Station, Antarctica, in August 1983. For comparison, winters in Yakutia, Russia regularly reach −60 to −70 °C

Water Freezing Point (0 °C / 32 °F)

The reference point for the Celsius scale and one of the two anchor points for Fahrenheit. 0 °C = 32 °F = 273.15 K. Defined at normal atmospheric pressure (101,325 Pa). Below this point water becomes ice

Room Temperature (~20–22 °C)

Standard room temperature by international norms is 20–22 °C = 68–72 °F = 293–295 K. This range is the reference for most physical measurements, product storage conditions and building climate standards

Normal Body Temperature (36.6 °C / 98.6 °F)

Normal human body temperature range: 36.1–37.2 °C (97–99 °F). The classic "98.6 °F" is the exact Fahrenheit conversion of 37 °C. A temperature above 38 °C (100.4 °F) is considered a fever. Above 40 °C (104 °F) is dangerous

Water Boiling Point (100 °C / 212 °F)

The second anchor point of the Celsius scale: 100 °C = 212 °F = 373.15 K at standard atmospheric pressure. At high altitude water boils below 100 °C — at 3,000 m it boils at ~90 °C. In a pressure cooker it boils above 100 °C

Oven Temperature for Baking (~180 °C)

180 °C = 356 °F = 453.15 K — typical baking temperature for most recipes. 200 °C (392 °F) for pastries and pizza. 250 °C (482 °F) is the upper limit of most domestic ovens. American recipes usually list oven temperatures in °F

Surface of the Sun (~5,526 °C)

The photosphere of the Sun is ~5,526 °C = 9,980 °F = 5,799 K. The solar corona exceeds 1,000,000 °C. The Sun's core reaches ~15,000,000 °C. For comparison, the surface of the Moon during the day reaches up to 127 °C (261 °F)

Temperature Scales Explained
Degree Celsius (°C)

The most widely used temperature scale in the world. Proposed by Swedish astronomer Anders Celsius in 1742. Reference points: 0 °C — water freezing, 100 °C — water boiling (at standard pressure). The official SI unit. Used in everyday life, medicine and meteorology everywhere except the United States

Degree Fahrenheit (°F)

Introduced by Gabriel Fahrenheit in 1724. Reference points: 32 °F — water freezing, 212 °F — water boiling. Formula: °F = °C × 9/5 + 32. Reverse: °C = (°F − 32) × 5/9. Used in the United States, the Cayman Islands and a few other territories. Normal body temperature: 98.6 °F = 37 °C

Kelvin (K)

The thermodynamic scale proposed by Lord Kelvin in 1848. Starts from absolute zero (0 K = −273.15 °C). One kelvin equals one degree Celsius in size. Formula: K = °C + 273.15. The standard in physics, chemistry and astrophysics. Water boils at 373.15 K. Kelvin values are never negative

Degree Rankine (°Ra)

An absolute scale based on Fahrenheit, proposed by William Rankine in 1859. 0 °Ra = absolute zero = −459.67 °F. The degree size matches Fahrenheit. Formula: °Ra = (°C + 273.15) × 9/5. Used in American engineering thermodynamics. Water boils at 671.67 °Ra

Degree Réaumur (°Ré)

Proposed by René Réaumur in 1730. Reference points: 0 °Ré — water freezing, 80 °Ré — water boiling. Formula: °Ré = °C × 4/5. Reverse: °C = °Ré × 5/4. Fell out of use in the 19th century. Survived longest in France, Switzerland and Russia. Now only encountered in historical cookbooks and old scientific texts

Frequently Asked Questions
How do I convert Celsius to Fahrenheit?

Formula: °F = °C × 9/5 + 32. Examples: 0 °C = 32 °F, 20 °C = 68 °F, 37 °C = 98.6 °F, 100 °C = 212 °F. Quick mental estimate: multiply °C by 2 and add 30 — gives a result within ~2 °F. Exact multiply factor is 1.8, not 2.

How do I convert Fahrenheit to Celsius?

Formula: °C = (°F − 32) × 5/9. Examples: 32 °F = 0 °C, 72 °F ≈ 22 °C, 98.6 °F = 37 °C, 212 °F = 100 °C. At −40 both scales meet: −40 °F = −40 °C — the only point where Fahrenheit and Celsius are equal.

How do I convert Celsius to Kelvin?

Simply add 273.15: K = °C + 273.15. Examples: 0 °C = 273.15 K, 20 °C = 293.15 K, 100 °C = 373.15 K. Reverse: °C = K − 273.15. Kelvin is never negative — it starts at absolute zero, the coldest possible temperature.

What is normal body temperature in Fahrenheit?

Normal body temperature is 36.6 °C ≈ 97.9 °F. The commonly cited 98.6 °F is the exact conversion of 37 °C. The healthy range is 97–99 °F (36.1–37.2 °C). A fever starts at 100.4 °F (38 °C). Above 104 °F (40 °C) is considered dangerous.

At what temperature are Celsius and Fahrenheit the same?

At −40 degrees. −40 °C = −40 °F exactly. This is the only point where both scales show the same number. You can verify: −40 × 9/5 + 32 = −72 + 32 = −40 °F. A useful fact for extreme cold weather contexts.

What is absolute zero?

Absolute zero is the lowest theoretically possible temperature: 0 K = −273.15 °C = −459.67 °F. At this point molecules would completely stop their thermal motion. It is physically unachievable — only approachable. It defines the zero point of the Kelvin and Rankine scales.

What is the difference between Kelvin and Celsius?

The degree size is identical: 1 K = 1 °C difference. The only difference is the zero point. Celsius: 0 °C = water freezing. Kelvin: 0 K = absolute zero (−273.15 °C). So Kelvin = Celsius + 273.15. Kelvin is used in science; Celsius in everyday life.

What are the Rankine and Réaumur scales used for?

Rankine (°Ra) is an absolute scale based on Fahrenheit, used in American engineering thermodynamics: 0 °Ra = absolute zero, degree size = Fahrenheit degree. Réaumur (°Ré) is an 18th-century scale where boiling = 80 °Ré. Now obsolete — only found in historical texts and old French recipes.

Temperature Converter — How to Convert Between Celsius, Fahrenheit and Kelvin

Temperature is one of the most commonly encountered physical quantities in daily life. Most of the world uses degrees Celsius, the United States uses Fahrenheit, and science uses Kelvin. The same temperature looks completely different in each scale: 100 °C = 212 °F = 373.15 K. This free online temperature converter instantly translates between all five scales — no manual formulas needed.

How to Convert Celsius to Fahrenheit and Back

The formula from Celsius to Fahrenheit is: °F = °C × 9/5 + 32. Key reference points: 0 °C = 32 °F (freezing), 20 °C = 68 °F (room temperature), 37 °C = 98.6 °F (body temperature), 100 °C = 212 °F (boiling). Reverse formula: °C = (°F − 32) × 5/9. One useful fact worth remembering: at −40 degrees both scales show the same number — −40 °C = −40 °F. For a quick mental estimate, double the Celsius value and add 30 to get an approximate Fahrenheit result within ~2 °F.

How to Convert Celsius and Fahrenheit to Kelvin

Converting Celsius to Kelvin is the simplest of all: K = °C + 273.15. So water boils at 373.15 K, room temperature is ~293 K, and absolute zero is 0 K = −273.15 °C. To convert Fahrenheit to Kelvin: K = (°F + 459.67) × 5/9. Kelvin can never be negative — it starts at absolute zero. The size of one kelvin equals one degree Celsius, so temperature differences are the same in both scales.

Practical Reference Points — Body, Oven and Weather

A few reference points make everyday conversions much easier. Normal body temperature: 37 °C = 98.6 °F. Fever threshold: 38 °C = 100.4 °F. Room temperature: 20 °C = 68 °F. Typical baking oven: 180 °C = 356 °F. If a US weather forecast says "90 °F" — that is 32 °C, a hot summer day. Freezing: 32 °F = 0 °C. When reading American recipes, always check whether oven temperatures are in °F — they usually are.

Rankine and Réaumur — Rare but Real Scales

Rankine (°Ra) is an absolute thermodynamic scale built on Fahrenheit: 0 °Ra = absolute zero, and the degree size matches Fahrenheit. Used in American engineering applications such as aerospace and heat engine calculations. Water boils at 671.67 °Ra. Réaumur (°Ré) is an 18th-century scale where water freezes at 0 °Ré and boils at 80 °Ré — formula: °Ré = °C × 0.8. Now obsolete but occasionally found in old European cookbooks and historical scientific texts. Use the converter above to translate any of these scales instantly.

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