Quick answer
Temperature conversion uses °F = °C × 9/5 + 32 and K = °C + 273.15. 100 °C equals 212 °F.
Enter a value, choose the units and decimals. The calculator returns the converted temperature.
Related tools: Wet Bulb Temperature Calculator: Wet-bulb temperature from air temperature and relative humidity (Stull's formula). Volume Converter: Convert litres, gallons, cups, spoons and more.
How to use the Temperature Converter
- Enter value.
- Choose from: Celsius (°C), Fahrenheit (°F), Kelvin (K) and Rankine (°R).
- Choose to: Celsius (°C), Fahrenheit (°F), Kelvin (K) and Rankine (°R).
- Enter decimal places (between 0 and 10). It starts at 4.
- Press Calculate to see the result, and use Reset to start again.
| Input | What to enter | Allowed values |
|---|---|---|
| Value | A number | — |
| From | Choose one: Celsius (°C); Fahrenheit (°F); Kelvin (K); Rankine (°R) | Starts at Celsius (°C) |
| To | Choose one: Celsius (°C); Fahrenheit (°F); Kelvin (K); Rankine (°R) | Starts at Fahrenheit (°F) |
| Decimal places | A number | ≥ 0, ≤ 10, starts at 4 |
Formula and method
Formula
Convert to the base unit, then to the target unit (see methodology).
IEEE-754 double precision; displayed to the chosen number of decimal places (default 4). Very small or large results are shown in scientific notation.
Every unit is defined by an exact or published factor to the base unit (kelvin). The value is multiplied by the source factor and divided by the target factor.
Worked examples
These examples are verified: each one is an automated test case that the live calculator must reproduce exactly.
Example 1
Inputs: Value = 100; From = Celsius (°C); To = Fahrenheit (°F); Decimal places = 4.
| Result | Value |
|---|---|
| Celsius (°C) → Fahrenheit (°F) | 212 |
| Input | 100 Celsius (°C) |
Example 2
Inputs: Value = -40; From = Fahrenheit (°F); To = Celsius (°C); Decimal places = 4.
| Result | Value |
|---|---|
| Fahrenheit (°F) → Celsius (°C) | -40 |
| Input | -40 Fahrenheit (°F) |
Example 3
Inputs: Value = 0; From = Kelvin (K); To = Celsius (°C); Decimal places = 2.
| Result | Value |
|---|---|
| Kelvin (K) → Celsius (°C) | -273.15 |
| Input | 0 Kelvin (K) |
The first line is the headline result (celsius (°C) → Fahrenheit (°F)). Below it the temperature Converter lists input, which describe the same case from other angles. IEEE-754 double precision; displayed to the chosen number of decimal places (default 4). Very small or large results are shown in scientific notation.
Reference points
Water freezes at 0 °C = 32 °F = 273.15 K and boils at 100 °C = 212 °F = 373.15 K. Body temperature is about 37 °C = 98.6 °F. −40 is the same in Celsius and Fahrenheit.
Differences versus readings
A change of 1 °C equals a change of 1.8 °F, but readings need the offset of 32. Kelvin has no degree sign and starts at absolute zero, 0 K = −273.15 °C.
How the result changes with value
Holding every other input at the first worked example, this table changes only value. It shows how sensitive the answer is to that one value; each row was produced by running this calculator.
| Value | Celsius (°C) → Fahrenheit (°F) | Input |
|---|---|---|
| 50 | 122 | 50 Celsius (°C) |
| 100 | 212 | 100 Celsius (°C) |
| 200 | 392 | 200 Celsius (°C) |
| 400 | 752 | 400 Celsius (°C) |
What happens with invalid input
These messages are produced by the calculator itself, so you know what to fix.
- Value: left empty shows "Enter value." beside that field and no result.
Choosing between the Temperature Converter and similar calculators
Each row shows what a related calculator on this site asks for and what it returns, so you can pick the one that matches your question.
| Calculator | You enter | It returns |
|---|---|---|
| [Oven Temperature Converter](/cooking/oven-temperature-calculator/) | convert | Temperature |
| [Wet Bulb Temperature Calculator](/science/wet-bulb/) | air temperature and relative humidity | Wet-bulb temperature |
| [Volume Converter](/converters/volume-converter/) | value, from and to | US gallon → Litre (L) |
| [Weight Converter](/converters/weight-converter/) | value, from and to | Pound (lb) → Gram (g) |
| [Length Converter](/converters/length-converter/) | value, from and to | Mile (mi) → Kilometre (km) |
Background: unit conversion
Many customary units are defined exactly in terms of metric ones: since the 1959 International Yard and Pound Agreement an inch is exactly 2.54 cm and a pound is exactly 0.45359237 kg (NIST SP 811 lists these). So most length and mass conversions are exact apart from the rounding of the displayed result.
To convert, multiply the value by the source unit's factor to reach the base unit, then divide by the target unit's factor; the unit table on this page lists every factor used. Temperature and fuel economy are the exceptions, because they are not simple multiples.
Assumptions and limitations
- Negative values are allowed
- Zero converts to zero (except L/100 km, where zero is invalid)
- Units from different quantities cannot be converted
- Very large or tiny results switch to exponent notation
If a required value is empty, not a number, or outside its allowed range, the form marks that field with a message and shows no result instead of a misleading number. The automated checks deliberately try invalid entries for value to confirm this.
Frequently asked questions
What is 0 °F in Celsius?
0 °F is −17.78 °C, from (0 − 32) × 5 ÷ 9.
How do I convert °F to °C?
Subtract 32 and multiply by 5/9.
What is absolute zero?
Absolute zero is 0 K, which is −273.15 °C or −459.67 °F; select Kelvin as the source unit and 0 as the value.
What does the Temperature Converter calculate?
Celsius, Fahrenheit, Kelvin and Rankine. It returns Celsius (°C) → Fahrenheit (°F) and Input.
What formula does the Temperature Converter use?
Convert to the base unit, then to the target unit (see methodology). Every unit is defined by an exact or published factor to the base unit (kelvin).
What does the “From” option change?
It sets how the temperature is worked out. The choices are Celsius (°C), Fahrenheit (°F), Kelvin (K) and Rankine (°R).
What is an example of a temperature result?
With value 100, from Celsius (°C), to Fahrenheit (°F) and decimal places 4, the celsius (°C) → Fahrenheit (°F) is 212.
Where does the method come from?
The method follows: NIST SP 811 (2008), Appendix B.8: K = °C + 273.15; °F = °C × 9/5 + 32; Rankine = K × 9/5.
Related calculators
- Wet Bulb Temperature Calculator — Wet-bulb temperature from air temperature and relative humidity (Stull's formula).
- Volume Converter — Convert litres, gallons, cups, spoons and more.
- Weight Converter — Convert kilograms, pounds, ounces, stone and more.
- Length Converter — Convert between metric and imperial lengths.
- Energy Converter — Convert joules, calories, kWh, BTU and more.
Sources
- NIST SP 811 (2008), Appendix B.8: K = °C + 273.15; °F = °C × 9/5 + 32
- Rankine = K × 9/5
Content last reviewed 2026-11-04. Formulas and worked examples are checked by automated tests against independently computed values.