Temperature Converter
Convert between Celsius, Fahrenheit, Kelvin and Rankine instantly. Enter a temperature in either field to see the equivalent, the right formula and a conversion chart. Baking? Use the oven Gas Mark guide below.
Convert Temperature Instantly
Type a value in either box. Unlike ordinary unit factors, most temperature conversions use an offset as well as a multiplier.
20 °C equals 68 °F
Popular temperature conversions
How to Use This Temperature Converter
Use this free calculator to translate one temperature reading into another scale. It works for weather forecasts, science exercises, technical specifications and everyday temperatures.
Enter your temperature
Type a value into From or To. Negative temperatures are supported in Celsius and Fahrenheit.
Select the scales
Choose °C, °F, K or °R. Use Swap to reverse the conversion and the quick buttons to change the pair.
Read and copy
See the result, the formula and the updated comparison chart. Copy the answer with its unit symbol.
Temperature Conversion Formulas
Temperature scales do not all begin at the same zero point. Celsius and Fahrenheit require both multiplication and an offset, while Kelvin and Rankine are absolute-temperature scales. That's why you cannot convert temperatures simply by multiplying by one fixed factor for every pair.
Common formulas
Fahrenheit = (Celsius × 9/5) + 32
Celsius = (Fahrenheit − 32) × 5/9
Kelvin = Celsius + 273.15
Rankine = Kelvin × 9/5
Example: 25°C to °F
Multiply 25 by 9/5, then add 32. The result is 77°F.
Example: 300 K to °C
Subtract 273.15 from 300. The result is 26.85°C.
Live formula example for your selected scales: 20 °C converts to 68 °F.
Temperature Conversion Chart
This table updates when you change the From or To scales. The calculator treats the values as actual temperatures, not temperature differences. Any sample below absolute zero is excluded.
| Celsius (°C) | Fahrenheit (°F) |
|---|---|
| −40 | −40 |
| 0 | 32 |
| 20 | 68 |
| 100 | 212 |
Display values are rounded for readability. Reference formulas use the defined temperature-scale relationships.
Celsius, Fahrenheit, Kelvin and Rankine Explained
Each temperature scale serves a different purpose. The same physical temperature can have four different numbers depending on the scale.
Absolute zero: 0 K = −273.15°C = −459.67°F = 0°R. This calculator rejects physical temperature readings below that limit. Temperature differences follow different rules: a change of 1°C equals a change of 1 K, but equals 1.8°F.
Common Temperature Reference Points
These familiar temperatures make it easier to check a conversion at a glance. Water's freezing and boiling temperatures are approximate reference points under standard atmospheric conditions.
| Example | Celsius | Fahrenheit | Kelvin |
|---|---|---|---|
| Same value on °C and °F scales | −40°C | −40°F | 233.15 K |
| Water freezes (approx.) | 0°C | 32°F | 273.15 K |
| Mild room temperature | 20°C | 68°F | 293.15 K |
| Warm day | 30°C | 86°F | 303.15 K |
| Water boils at sea level (approx.) | 100°C | 212°F | 373.15 K |
Oven Gas Mark to Celsius and Fahrenheit
UK recipes sometimes use Gas Marks instead of degrees. Select a setting to see its commonly quoted conventional-oven Celsius, Fahrenheit and fan-oven equivalents. These are approximate cooking settings, not mathematically exact temperature-scale conversions.
Fan values are common recipe guidance, often around 20°C lower than conventional settings. Follow your oven's instructions.
| Gas Mark | Conventional °C (approx.) | Recipe °F (approx.) | Fan °C (guide) |
|---|---|---|---|
| ¼ | 110°C | 225°F | 90°C |
| ½ | 120°C | 250°F | 100°C |
| 1 | 140°C | 275°F | 120°C |
| 2 | 150°C | 300°F | 130°C |
| 3 | 160°C | 325°F | 140°C |
| 4 | 180°C | 350°F | 160°C |
| 5 | 190°C | 375°F | 170°C |
| 6 | 200°C | 400°F | 180°C |
| 7 | 220°C | 425°F | 200°C |
| 8 | 230°C | 450°F | 210°C |
| 9 | 240°C | 475°F | 220°C |
Oven dials, fan settings and published conversion charts can differ. For example, 350°F equals about 176.7°C mathematically, though many baking charts round Gas Mark 4 to 180°C.
Frequently Asked Questions
What is 20°C in Fahrenheit?
20°C equals exactly 68°F. Multiply 20 by 9/5 and add 32.
What is 100°F in Celsius?
100°F equals approximately 37.78°C. Subtract 32 and multiply by 5/9.
How do I convert Celsius to Kelvin?
Add 273.15 to the Celsius value. For example, 25°C = 298.15 K. Kelvin is written without a degree sign.
What is Rankine used for?
Rankine is an absolute thermodynamic temperature scale with Fahrenheit-sized increments, used in some engineering fields. Kelvin and Rankine both begin at absolute zero.
At what temperature are Celsius and Fahrenheit equal?
Both scales read −40 at the same physical temperature: −40°C = −40°F.
Can Kelvin or Rankine be negative?
Not for ordinary absolute thermodynamic temperatures. These scales begin at absolute zero. The calculator therefore does not accept values below 0 K or 0°R.
Can I convert temperature differences with this tool?
This calculator converts absolute readings, not differences. For changes in temperature, 1°C change = 1 K change, and 1°F change = 5/9°C change. Don't apply the 32-degree offset to a temperature difference.
What Gas Mark is 180°C?
A conventional oven at about 180°C is commonly listed as Gas Mark 4. A recipe may suggest approximately 160°C for a fan oven, but oven manuals take priority.
Why does an oven chart differ from the exact Fahrenheit conversion?
Oven temperatures in recipes often use rounded conventional settings. For example, 350°F is roughly 176.7°C, but is commonly printed as 180°C (Gas Mark 4). Both represent approximate cooking settings, rather than an exact mathematical identity.
Related Conversion Calculators
Looking for a different kind of measurement? Try another calculator from the same conversion directory.
Temperature Standards and Sources
The absolute temperature-scale conversions follow the definitions in the NIST temperature conversion reference and NIST Guide to the SI. Oven Gas Mark values use common recipe-chart approximations as described in Which?'s oven conversion table.
Precision note: Displays are rounded for readability. Formula calculations use JavaScript double-precision arithmetic. For scientific or regulated applications, check measurement uncertainty and required significant figures independently.