Temperature Converter

F equals 9/5 times C plus 32; K equals C plus 273.15; R equals 9/5 times (C plus 273.15)

Converted =

212 °F | 373.15 K | 671.67 °R
UnitValue
Celsius (°C)100
Fahrenheit (°F)212
Kelvin (K)373.15
Rankine (°R)671.67
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Common Temperature Reference Points

Description°C°FK°R
Absolute Zero-273.15-459.6700
Water Freezing Point032273.15491.67
Room Temperature2068293.15527.67
Body Temperature3798.6310.15558.27
Water Boiling Point100212373.15671.67

Celsius to Fahrenheit

The Celsius scale places 0 at freezing and 100 at boiling. Fahrenheit uses 32 and 212 for the same points, spanning 180 degrees. Each Celsius degree is 1.8 times a Fahrenheit degree.

F = (9/5) × C + 32

How It Works

Temperature scales measure thermal energy using different reference points and degree intervals. Every conversion formula accounts for two differences between scales: the offset (where zero falls) and the size of each degree. Celsius and Kelvin share degree size but differ by 273.15 in offset. Fahrenheit and Rankine share degree size but differ by 459.67. Between Celsius and Fahrenheit, both the offset and degree size differ, requiring a multiply-then-shift formula.

Example Problem

Normal human body temperature is 37°C. Convert to Fahrenheit, Kelvin, and Rankine.

  1. Fahrenheit: F = (9/5) × 37 + 32 = 66.6 + 32 = 98.6°F
  2. Kelvin: K = 37 + 273.15 = 310.15 K
  3. Rankine: R = (9/5)(37 + 273.15) = (9/5)(310.15) = 558.27°R

A fever is typically above 38°C (100.4°F). Converting 101.3°F to Celsius: (5/9)(101.3 − 32) = 38.5°C, confirming a mild fever.

Frequently Asked Questions

What is absolute zero?

Absolute zero is the lowest possible temperature where all molecular motion ceases. It corresponds to 0 Kelvin, 0° Rankine, −273.15°C, or −459.67°F.

Why are there different temperature scales?

Different temperature scales were developed for different purposes. Celsius is used worldwide for everyday measurement, Fahrenheit is common in the United States, Kelvin is the scientific standard starting at absolute zero, and Rankine serves engineering needs using Fahrenheit-sized degrees from absolute zero.

At what temperature are Celsius and Fahrenheit equal?

Celsius and Fahrenheit are equal at −40 degrees. Setting C = F in the formula F = (9/5)C + 32 solves to C = −40.

How do I quickly estimate Celsius to Fahrenheit?

A quick mental shortcut: double the Celsius value and add 30. For example, 20°C gives roughly 70°F (exact: 68°F). This works well for everyday temperatures.

What is the Rankine scale used for?

The Rankine scale is used in engineering and thermodynamics in the United States, particularly for the Rankine cycle in steam turbines and power plants. Like Kelvin, it starts at absolute zero but uses Fahrenheit-sized degree intervals.

Why does the United States still use Fahrenheit?

The United States adopted Fahrenheit during the colonial era when it was the dominant scale in the British Empire. Although Congress passed the Metric Conversion Act in 1975, the transition never gained widespread public momentum, so Fahrenheit persists for daily use while Celsius and Kelvin dominate in American scientific and military contexts.

How do you convert Kelvin to Fahrenheit directly?

To convert Kelvin to Fahrenheit, use the formula F = (9/5)(K − 273.15) + 32. For example, 300 K converts to (9/5)(300 − 273.15) + 32 = 80.33°F. You can also go through Rankine: R = (9/5) × K, then F = R − 459.67.

Is there a temperature where Kelvin and Fahrenheit are equal?

Yes. Setting K = F in the conversion formula and solving yields approximately 574.59. So 574.59 Kelvin equals 574.59°F (about 301.44°C).

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