The Temperature Calculator converts a value between any two of the four common temperature scales: Celsius, Fahrenheit, Kelvin and Rankine. Pick a source scale and a target scale, enter the value, and the tool shows the exact formula used along with the substituted arithmetic.
Temperature scales differ in two ways: where they place zero, and how large one degree is. Celsius and Kelvin share a degree size but different zero points; Fahrenheit and Rankine share a degree size but different zero points; and Celsius/Kelvin degrees differ in size from Fahrenheit/Rankine degrees by a factor of 9/5. This page routes any pair through the right combination of scaling and shifting.
Convert between the four temperature scales
Every conversion in this family reduces to two possible operations: multiplying by 9/5 or 5/9 to change degree size, and adding or subtracting an offset to change the zero point. The table below lists the direct formula for each of the twelve ordered pairs.
°F = (°C × 9/5) + 32 °C = (°F − 32) × 5/9
K = °C + 273.15 °C = K − 273.15
°R = (°C + 273.15) × 9/5 °C = (°R × 5/9) − 273.15
K = (°F − 32) × 5/9 + 273.15 °F = (K − 273.15) × 9/5 + 32
°R = °F + 459.67 °F = °R − 459.67
°R = K × 9/5 K = °R × 5/9Worked example: convert 20 °C to each of the other three scales.
Fahrenheit: 20 × 1.8 + 32 = 68 °F Kelvin: 20 + 273.15 = 293.15 K Rankine: (20 + 273.15) × 1.8 = 527.67 °R
Understand degree size versus zero point
Two separate ideas explain every formula on this page. Degree size answers "how much does one unit of this scale represent?" Celsius and Kelvin use the same size; Fahrenheit and Rankine use a smaller size, in a 5-to-9 ratio against Celsius and Kelvin.
Zero point answers "where does this scale start counting from?" Kelvin and Rankine start at absolute zero; Celsius starts at water's freezing point; Fahrenheit starts at a historical reference roughly matching a brine mixture's freezing point.
Any conversion that keeps the same degree size (Celsius↔Kelvin, Fahrenheit↔Rankine) needs only addition or subtraction. Any conversion that changes degree size (Celsius↔Fahrenheit, Kelvin↔Rankine, and the cross pairs) needs a multiplication or division as well.
Check every scale at three reference points
| Celsius | Fahrenheit | Kelvin | Rankine |
|---|---|---|---|
| −273.15 °C | −459.67 °F | 0 K | 0 °R |
| 0 °C | 32 °F | 273.15 K | 491.67 °R |
| 100 °C | 212 °F | 373.15 K | 671.67 °R |
Absolute zero is the one point where all four scales agree that nothing can be colder, though they use very different numbers to say so. Water's freezing and boiling points anchor the everyday range that Celsius and Fahrenheit were originally built around.
Work through a full conversion by hand
Take a temperature of 50 °F and convert it to Kelvin. 1. Convert to Celsius first. (50 − 32) × 5/9 = 18 × 5/9 = 10 °C. 2. Add the Kelvin offset. 10 + 273.15 = 283.15 K.
Routing an unfamiliar pair through Celsius, the scale in the middle of the size-and-offset relationships, is often the easiest way to avoid combining constants incorrectly by hand.
The Temperature Calculator does this internally regardless of which two scales are selected.
Choose the right scale for the task
Celsius is standard for weather, cooking and most non-US science education. Fahrenheit remains standard in US weather reporting and home use. Kelvin is required for scientific formulas involving absolute temperature, such as gas laws and radiation equations. Rankine appears in some US engineering and thermodynamics work where Fahrenheit-sized degrees are conventional but an absolute-zero reference is needed.
Convert practical reference temperatures across all four scales
Everyday reference points show how the twelve formulas connect. An oven set to 180 °C converts to 180 × 1.8 + 32 = 356 °F, 180 + 273.15 = 453.15 K, and 453.15 × 1.8 = 815.67 °R.
A household freezer at −18 °C converts to −18 × 1.8 + 32 = −0.4 °F, −18 + 273.15 = 255.15 K, and 255.15 × 1.8 = 459.27 °R.
A fever reading of 38.5 °C converts to 38.5 × 1.8 + 32 = 101.3 °F, 38.5 + 273.15 = 311.65 K, and 311.65 × 1.8 = 560.97 °R.
Each row applies the same Celsius-based formulas already shown above, just at values outside the freezing-to-boiling range. Working through a cold, a warm, and a hot example across all four scales is a fast way to confirm the Temperature Calculator applies its formulas consistently.
Frequently asked questions
How do I convert between any two temperature scales?
Select the source and target scales, enter the value, and the tool applies the matching formula automatically, whether that requires only an offset (Celsius↔Kelvin, Fahrenheit↔Rankine) or both a scaling factor and an offset (Celsius↔Fahrenheit and the remaining pairs).
What is the fastest way to convert Celsius to Fahrenheit?
Multiply by 9/5 and add 32: °F = (°C × 9/5) + 32.
Which scales share the same degree size?
Celsius and Kelvin share one degree size. Fahrenheit and Rankine share a smaller degree size, in a 5-to-9 ratio to Celsius and Kelvin.
Which scales are anchored at absolute zero?
Kelvin and Rankine both start counting from absolute zero. Celsius and Fahrenheit use other historical reference points instead.
What is absolute zero on all four scales?
Absolute zero is −273.15 °C, −459.67 °F, 0 K and 0 °R.
Why do some conversions need multiplication and others only addition?
Conversions between scales that share a degree size (Celsius↔Kelvin, Fahrenheit↔Rankine) need only an offset. Conversions between scales with different degree sizes need a multiplication or division as well.
Is there a dedicated calculator for just one pair, like Celsius to Fahrenheit?
Yes. Single-pair pages such as the Celsius to Fahrenheit Calculator and Celsius to Kelvin Calculator focus on one conversion with more worked detail, while this page handles any combination of the four scales.
Summary
Every temperature conversion combines two possible operations: a 9/5 or 5/9 scaling factor when degree sizes differ, and an additive offset when zero points differ. Celsius and Kelvin share a degree size and need only an offset; Fahrenheit and Rankine do the same.
Crossing between the two families, such as Celsius to Fahrenheit or Kelvin to Rankine, needs both operations. This calculator applies the correct combination for any of the twelve ordered pairs among Celsius, Fahrenheit, Kelvin and Rankine.