The Temperature Conversion Calculator converts among Celsius, Fahrenheit, Kelvin, and Rankine. Temperature scales include offsets, so conversion is not a single multiply like length. Enter a value on any scale, read the others with the active formula and substituted steps, and see all four results together for comparison.
Values below absolute zero (0 K, which is −273.15 °C or −459.67 °F) are refused. Reference points for freezing, body temperature, and boiling sit beside the converter for quick sanity checks against everyday experience.
Convert between temperature scales
The Temperature Conversion Calculator accepts Celsius (°C), Fahrenheit (°F), Kelvin (K), and Rankine (°R). Choose a source scale, enter the number, and read any target scale. Internal routing may pass through Kelvin for consistency, while the formula line still shows the pair the user selected when a direct formula exists.
Unlike mass or length converters, temperature needs both a scale factor and an offset for Celsius ↔ Fahrenheit. Kelvin and Rankine are absolute scales with zero at absolute zero, so they convert to Celsius or Fahrenheit with shifts as well as optional degree-size changes.
Live recalculation updates every field when one value changes. Blocking sub-absolute inputs prevents nonsensical negative kelvin results from typos.
Convert Celsius to Fahrenheit
Celsius converts to Fahrenheit with multiply by 9/5 (or 1.8) then add 32.
°F = (°C × 9/5) + 32Worked example: convert 25 °C to Fahrenheit.
1. Multiply by 9/5. 25 × 1.8 = 45.
2. Add 32. 45 + 32 = 77 °F.
So 25 °C equals 77 °F. Freezing water at 0 °C is 32 °F; boiling at 100 °C is 212 °F under standard conditions used for these fixed points. The Temperature Conversion Calculator prints the substituted steps for the entered Celsius value.
Convert Fahrenheit to Celsius
Fahrenheit converts to Celsius by subtracting 32, then multiplying by 5/9.
°C = (°F − 32) × 5/9Worked example: convert 68 °F to Celsius.
1. Subtract 32. 68 − 32 = 36.
2. Multiply by 5/9. 36 × 5/9 = 20 °C.
Room-temperature figures around 68 to 72 °F land near 20 to 22 °C. The Temperature Conversion Calculator uses the exact 5/9 factor rather than a rough "minus thirty divide by two" estimate, though that estimate can still help mental checks.
Convert to and from Kelvin
Kelvin is the SI absolute temperature scale. Celsius converts to Kelvin by adding 273.15. Kelvin converts to Celsius by subtracting 273.15. One kelvin degree has the same size as one Celsius degree.
K = °C + 273.15
°C = K − 273.15Worked example: 25 °C → K.
25 + 273.15 = 298.15 K.
Absolute zero is 0 K by definition, equal to −273.15 °C. Scientific equations that use absolute temperature need kelvin (or rankine), not Celsius. The Temperature Conversion Calculator shifts by 273.15 for those pairs and still blocks any result that would imply T < 0 K.
Convert to and from Rankine
Rankine is an absolute scale that uses Fahrenheit-sized degrees. Fahrenheit converts to Rankine by adding 459.67. Rankine converts to Fahrenheit by subtracting 459.67. Rankine also equals kelvin × 9/5, because Fahrenheit degrees are 9/5 the size of Celsius/kelvin degrees.
°R = °F + 459.67
°R = K × 9/5Water freezes at 491.67 °R (corresponding to 32 °F and 273.15 K). Absolute zero is 0 °R as well as 0 K. US engineering texts sometimes prefer Rankine when Fahrenheit is the everyday scale but absolute temperature is required for gas laws.
See a temperature in all four scales
Entering one value updates Celsius, Fahrenheit, Kelvin, and Rankine together. A classroom reference at 25 °C reads 77 °F, 298.15 K, and 536.67 °R in the same panel.
| Checkpoint | °C | °F | K | °R |
|---|---|---|---|---|
| Absolute zero | −273.15 | −459.67 | 0 | 0 |
| Ice point | 0 | 32 | 273.15 | 491.67 |
| Body (approx.) | 37 | 98.6 | 310.15 | 558.27 |
| Boiling (std) | 100 | 212 | 373.15 | 671.67 |
The Temperature Conversion Calculator uses these anchors as checks, not as climate models. Local boiling points change with altitude; the table's 100 °C / 212 °F pair is the standard sea-level reference taught with the formulas.
Read the temperature reference points
Absolute zero is the lower bound: 0 K, −273.15 °C, −459.67 °F, 0 °R. The ice point of water is 0 °C / 32 °F under standard conditions used for scale definitions. Average human body temperature is often cited as 37 °C / 98.6 °F. Standard boiling is 100 °C / 212 °F.
Comparing a thermometer reading to these points catches unit mistakes quickly. A weather report of "30" is mild in Celsius and dangerously hot in Fahrenheit. The Temperature Conversion Calculator's four-scale view removes that ambiguity when copying values between regions.
FAQ
How do I convert Celsius to Fahrenheit?
To convert Celsius to Fahrenheit, multiply by 9/5 and add 32. For example, 25 × 9/5 + 32 = 77 °F. The Temperature Conversion Calculator shows that formula with substituted steps.
What is the formula for Fahrenheit to Celsius?
The Fahrenheit to Celsius formula is (°F − 32) × 5/9. For example, (68 − 32) × 5/9 = 20 °C. The Temperature Conversion Calculator applies that reverse formula.
Why is Kelvin used?
Kelvin is an absolute SI scale starting at absolute zero, required by many science formulas. The Temperature Conversion Calculator converts to kelvin by adding 273.15 to Celsius.
What is absolute zero?
Absolute zero is 0 K, equal to −273.15 °C and −459.67 °F. The Temperature Conversion Calculator blocks inputs colder than that physical limit.
What is Rankine?
Rankine is an absolute temperature scale with Fahrenheit-sized degrees. °R = °F + 459.67, and 0 °R is absolute zero. The Temperature Conversion Calculator includes Rankine beside Kelvin.
Is 37 °C normal body temperature?
Yes, 37 °C is the common reference for normal human body temperature, equal to 98.6 °F. Individual readings vary; the Temperature Conversion Calculator only converts the number entered.
Why can temperature not use a pure factor table?
Celsius and Fahrenheit zero points differ, so an offset is required in addition to a scale factor. The Temperature Conversion Calculator therefore shows full formulas, not only multiply/divide factors.
How do I convert 100 °C to Fahrenheit?
One hundred Celsius equals 212 °F, because 100 × 9/5 + 32 = 212. The Temperature Conversion Calculator returns that boiling-reference conversion for the Celsius input.
Summary
The Temperature Conversion Calculator converts Celsius, Fahrenheit, Kelvin, and Rankine using full scale formulas such as °F = °C × 9/5 + 32 and K = °C + 273.15. Rankine pairs with Fahrenheit through a 459.67 offset and with kelvin through a 9/5 factor.
Absolute zero is blocked, all four scales can update together, and reference points for freezing, body temperature, and boiling support quick checks. Temperature needs offsets, so this page stays separate from pure factor converters on the hub.