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)

100 °C converts to

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

Show Your Work

  1. 1. Start with the input temperature: C = 100 °C
  2. 2. F = (9/5 × 100) + 32 = 212 °F
  3. 3. K = 100 + 273.15 = 373.15 K
  4. 4. R = (100 + 273.15) × 9/5 = 671.67 °R
  5. 5. Answer = 212 °F, 373.15 K, 671.67 °R
Share:

Temperature Conversion Formula Guide

From Celsius

F = (9/5) × C + 32, K = C + 273.15, R = (C + 273.15) × 9/5

  • Use this when your input is already in Celsius.
  • Celsius and Kelvin share the same degree size.
  • Fahrenheit and Rankine use larger degree increments than Celsius.

From Fahrenheit

C = (F - 32) × 5/9, K = (F - 32) × 5/9 + 273.15, R = F + 459.67

  • Subtract 32 first because Fahrenheit and Celsius use different zero points.
  • Then scale by 5/9 to match Celsius-size degrees.
  • Rankine keeps Fahrenheit-size degrees but starts at absolute zero.

From Kelvin

C = K - 273.15, F = (K - 273.15) × 9/5 + 32, R = K × 9/5

  • Kelvin is the scientific absolute-temperature scale.
  • Kelvin and Celsius differ only by the 273.15 offset.
  • Converting Kelvin to Rankine changes degree size, not the zero reference.

From Rankine

C = R × 5/9 - 273.15, F = R - 459.67, K = R × 5/9

  • Rankine is the absolute-temperature partner of Fahrenheit.
  • Rankine and Kelvin both start at absolute zero.
  • Multiply by 5/9 to move from Rankine degrees to Kelvin/Celsius-sized degrees.

Worked Examples

Cooking

What is 180°C in Fahrenheit, Kelvin, and Rankine?

A baking recipe calls for a 180°C oven. Convert that setpoint into the other common temperature scales.

  1. Start with the Celsius temperature: C = 180°C.
  2. Convert to Fahrenheit: F = (9/5 × 180) + 32 = 356°F.
  3. Convert to Kelvin: K = 180 + 273.15 = 453.15 K.
  4. Convert to Rankine: R = (180 + 273.15) × 9/5 = 815.67°R.
  5. The same oven temperature is 356°F, 453.15 K, and 815.67°R.

This is a common kitchen conversion when a recipe uses Celsius but your oven uses Fahrenheit.

Weather

How cold is -4°F in Celsius, Kelvin, and Rankine?

A winter weather forecast reports -4°F. Convert it to the other temperature scales for science or travel use.

  1. Start with the Fahrenheit temperature: F = -4°F.
  2. Convert to Celsius: C = (-4 - 32) × 5/9 = -20°C.
  3. Convert Celsius to Kelvin: K = -20 + 273.15 = 253.15 K.
  4. Convert Fahrenheit to Rankine directly: R = -4 + 459.67 = 455.67°R.
  5. The same outdoor temperature is -20°C, 253.15 K, and 455.67°R.

Cold-weather engineering specs often use Kelvin or Rankine even when public weather reports use Fahrenheit.

Laboratory

What is 300 K in Celsius, Fahrenheit, and Rankine?

A laboratory process is documented at 300 K. Convert it for teams that prefer Celsius or Fahrenheit.

  1. Start with the Kelvin temperature: K = 300 K.
  2. Convert to Celsius: C = 300 - 273.15 = 26.85°C.
  3. Convert Celsius to Fahrenheit: F = (26.85 × 9/5) + 32 = 80.33°F.
  4. Convert Kelvin to Rankine: R = 300 × 9/5 = 540°R.
  5. The same process temperature is 26.85°C, 80.33°F, and 540°R.

Kelvin is the standard scientific temperature scale, so this conversion comes up often in lab, chemistry, and physics work.

Engineering

What is 1000°R in Fahrenheit, Celsius, and Kelvin?

A U.S. thermodynamics reference lists a heat-transfer condition at 1000°R. Convert it into the scales used by teammates working in metric or everyday units.

  1. Start with the Rankine temperature: R = 1000°R.
  2. Convert to Fahrenheit directly: F = 1000 - 459.67 = 540.33°F.
  3. Convert to Kelvin: K = 1000 × 5/9 = 555.56 K.
  4. Convert Kelvin to Celsius: C = 555.56 - 273.15 = 282.41°C.
  5. The same process temperature is 540.33°F, 555.56 K, and 282.41°C.

Rankine is common in U.S. thermodynamic engineering for steam-cycle and heat-transfer work where absolute temperature matters but Fahrenheit-sized degrees are preferred.

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

How It Works

Temperature conversion works by accounting for two differences between scales: where zero starts and how large each degree is. Celsius and Kelvin use the same size degree, but Kelvin starts 273.15 units above Celsius at absolute zero. Fahrenheit and Rankine also share the same size degree, but Rankine starts at absolute zero while Fahrenheit starts 459.67 degrees below it. When you convert between Celsius and Fahrenheit, or between Kelvin and Rankine, you must handle both the offset and the degree-size change. This converter does that instantly and shows all four scales at once so you can compare everyday, scientific, and engineering temperature systems on one screen.

Example Problem

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

  1. Start with the Celsius temperature: C = 37°C.
  2. Convert Celsius to Fahrenheit using F = (9/5 × C) + 32.
  3. Substitute the value: F = (9/5 × 37) + 32 = 66.6 + 32 = 98.6°F.
  4. Convert Celsius to Kelvin using K = C + 273.15, so K = 37 + 273.15 = 310.15 K.
  5. Convert Celsius to Rankine using R = (C + 273.15) × 9/5, so R = (37 + 273.15) × 9/5 = 558.27°R.
  6. The same temperature is 98.6°F, 310.15 K, and 558.27°R.

This is why body temperature appears as 98.6°F in the United States but 37°C in most medical references elsewhere.

Key Concepts

Absolute zero is the anchor point that connects Kelvin and Rankine to Celsius and Fahrenheit. Kelvin and Rankine never go below zero because they begin at absolute zero, while Celsius and Fahrenheit can be negative because their zero points were defined for practical measurement rather than thermodynamic limits. Another key concept is degree size: one Celsius degree equals one Kelvin unit, while one Fahrenheit degree equals one Rankine degree. That is why some conversions need only an offset, while others require both an offset and a multiplication factor.

Applications

  • Converting cooking temperatures between Celsius ovens and Fahrenheit recipes
  • Reading weather reports when traveling between countries that use different scales
  • Checking laboratory, chemistry, and physics temperatures reported in Kelvin
  • Interpreting engineering and thermodynamics values reported in Rankine
  • Comparing medical temperatures such as fever thresholds across Celsius and Fahrenheit
  • Building spreadsheets, calculators, or control systems that need consistent temperature units

Common Mistakes

  • Adding or subtracting the offset in the wrong order when converting Fahrenheit and Celsius
  • Forgetting that Kelvin and Rankine start at absolute zero, not at the freezing point of water
  • Using the same degree step for Celsius and Fahrenheit without applying the 9/5 or 5/9 scale factor
  • Rounding too early in a multi-step conversion, which can slightly shift the final answer
  • Assuming negative Kelvin or negative Rankine values are valid in normal physical temperature measurement
  • Treating Fahrenheit and Rankine as the same scale even though they use different zero references

Frequently Asked Questions

How do I convert Celsius to Fahrenheit?

Use the formula F = (9/5 × C) + 32. For example, 20°C becomes (9/5 × 20) + 32 = 68°F.

What is the formula for converting Celsius to Fahrenheit?

The exact formula is Fahrenheit = (9/5 × Celsius) + 32. To reverse it, use Celsius = (Fahrenheit - 32) × 5/9.

What is absolute zero?

Absolute zero is the lowest possible temperature in thermodynamics. It equals 0 K, 0°R, -273.15°C, and -459.67°F.

Why are there different temperature scales?

Different scales were created for different uses. Celsius became the everyday metric scale, Fahrenheit remained common in the United States, Kelvin is standard in science, and Rankine is used in some engineering systems that prefer Fahrenheit-sized degrees.

At what temperature are Celsius and Fahrenheit equal?

Celsius and Fahrenheit are equal at -40 degrees. So -40°C is exactly the same as -40°F.

Can Kelvin or Rankine be negative?

In ordinary thermodynamic temperature measurement, no. Kelvin and Rankine both begin at absolute zero, so values below 0 K or 0°R are not valid for normal physical temperatures.

How do I convert Kelvin to Fahrenheit directly?

Use F = (9/5 × (K - 273.15)) + 32. For example, 300 K converts to about 80.33°F.

What is Rankine used for?

Rankine is used in thermodynamics and engineering fields that work with absolute temperature but keep Fahrenheit-sized degrees, such as some power-cycle and heat-transfer calculations in the United States.

What is a quick way to estimate Celsius to Fahrenheit?

A rough mental shortcut is to double the Celsius value and add 30. It is not exact, but it gives a fast everyday estimate. For example, 20°C becomes about 70°F, while the exact answer is 68°F.

Reference: Exact scale anchors used here: 0°C = 32°F = 273.15 K = 491.67°R, and absolute zero = -273.15°C = -459.67°F = 0 K = 0°R.

Related Calculators

Related Sites