Temperature Converter
Unit Converters
Convert Celsius, Fahrenheit, Kelvin, or Rankine readings and temperature differences. Compare common reference points, copy every result, and share a conversion link.
Common reference temperatures
0 °C = 32 °F
Equivalent temperatures
Historical scale: Réaumur (°Ré)
Temperature scale
0.00°C · 32.00°F · 273.15 K · 491.67°R
How to use this tool
- Choose a conversion mode. Select Reading for an absolute temperature or Difference (ΔT) for a temperature change.
- Enter a value or choose a reference. Type a temperature or change, or select a common reference such as water freezing or room temperature.
- Select units. Choose the source and destination scales: Celsius, Fahrenheit, Kelvin, Rankine, or historical Réaumur.
- Read the results. The converted value and equivalents in every scale update instantly, rounded to 6 significant figures.
- Swap, clear, or share. Swap the direction, reset the converter, or copy a link that preserves the current value, units, and mode.
Celsius to Fahrenheit and Fahrenheit to Celsius
Celsius (°C) and Fahrenheit (°F) are the two scales most people encounter in daily life. The conversion formula is: °F = °C × 9/5 + 32. To reverse it: °C = (°F − 32) × 5/9. The two scales cross at exactly −40°, the one temperature that is the same in both Celsius and Fahrenheit.
Common temperature references
| Reference | °C | °F | K |
|---|---|---|---|
| Absolute zero | −273.15 | −459.67 | 0 |
| Dry ice (CO₂ sublimation) | −78.5 | −109.3 | 194.65 |
| Water freezes | 0 | 32 | 273.15 |
| Cold winter day | −10 | 14 | 263.15 |
| Comfortable room temperature | 20 | 68 | 293.15 |
| Human body temperature | 37 | 98.6 | 310.15 |
| Hot summer day | 40 | 104 | 313.15 |
| Oven: medium heat — convert to Gas Mark | 180 | 356 | 453.15 |
| Water boils (sea level) | 100 | 212 | 373.15 |
| C and F are equal | −40 | −40 | 233.15 |
The four temperature scales
Celsius (°C)
The Celsius scale was defined by the Swedish astronomer Anders Celsius in 1742. Its two anchors are the freezing point (0°C) and boiling point (100°C) of water at standard atmospheric pressure. The Celsius scale is used by most of the world for everyday temperature measurement and is the scientific standard alongside Kelvin.
Fahrenheit (°F)
Proposed by Daniel Gabriel Fahrenheit in 1724, the Fahrenheit scale was historically anchored to the freezing point of a brine solution (0°F) and human body temperature (96°F in the original, later adjusted). Water freezes at 32°F and boils at 212°F. The Fahrenheit scale is used primarily in the United States for everyday temperatures. Its 180-degree span between freezing and boiling (vs. 100° in Celsius) gives slightly finer resolution for typical weather and body temperatures.
Kelvin (K)
The Kelvin scale (the SI base unit of thermodynamic temperature) begins at absolute zero (the lowest theoretically possible temperature) and uses the same degree size as Celsius. 0 K = −273.15°C. Kelvin values are never negative by definition. Kelvin is used throughout physics, chemistry, and engineering where absolute temperatures are required. For example, in the ideal gas law (PV = nRT), where T must be in Kelvin.
The 2019 SI redefinition fixed the Kelvin by tying it to the Boltzmann constant (k = 1.380649 × 10⁻²³ J/K), making it more precise than the previous triple-point-of-water definition.
Rankine (°R)
The Rankine scale uses the same size degree as Fahrenheit but starts at absolute zero, analogous to Kelvin's relationship with Celsius. 0°R = absolute zero = −459.67°F. Water freezes at 491.67°R and boils at 671.67°R. Rankine is used in some US engineering contexts, particularly in thermodynamics and aerodynamics, where absolute temperatures are needed but Fahrenheit-sized degrees are preferred.
Why temperature conversion is different from other unit conversions
Most unit conversions are purely multiplicative: multiply by a fixed factor. Temperature is different because Celsius and Fahrenheit have different zero points as well as different degree sizes. Converting between them requires both a multiplication and an addition (or subtraction). Kelvin and Rankine, being absolute scales that start at the same physical zero, only require a multiplication by 9/5 (or 5/9) to convert between themselves.
Reading vs. temperature difference
A temperature reading describes a point on a scale, so conversions between Celsius and Fahrenheit include the 32-degree offset. A temperature difference describes only how much warmer or cooler something became, so it uses the degree-size ratio without an offset. For example, a reading of 10°C is 50°F, while an increase of 10°C is an increase of 18°F. Use Difference (ΔT) for laboratory measurements, weather changes, or heat-transfer calculations; use Reading for an actual thermometer value.
A quick mental estimate for everyday weather is to double a Celsius value and add 30. It is deliberately approximate: 20°C becomes about 70°F, while the exact result is 68°F. For cooking, scientific work, and precise measurements, use the converter's exact result.
Practical cooking temperatures
| Reference | °C | °F |
|---|---|---|
| Rare steak (internal) | 52 | 125 |
| Medium steak (internal) | 60 | 140 |
| Well-done steak (internal) | 71 | 160 |
| Poultry - safe minimum (USDA) | 74 | 165 |
| Bread - internal done | 88–93 | 190–200 |
| Soft ball candy stage | 115 | 240 |
| Hard crack candy stage | 149 | 300 |
| Deep frying oil | 175–190 | 347–375 |
For ingredient amounts and recipe scaling, use the Cooking Converter. If a recipe is written for a conventional oven, the Air Fryer Converter can help adapt its temperature.
Weather context anchors
A quick reference for travelers or anyone switching between Celsius and Fahrenheit for everyday weather:
| Condition | °C | °F |
|---|---|---|
| Freezing point of water | 0 | 32 |
| Cold day (wear a heavy coat) | 5 | 41 |
| Cool day (jacket needed) | 10 | 50 |
| Mild / comfortable | 20 | 68 |
| Warm / t-shirt weather | 25 | 77 |
| Hot day | 30 | 86 |
| Very hot / dangerous heat | 40 | 104 |
| Heat stroke risk | 43+ | 110+ |
Temperature alone does not describe how weather feels. For humid heat, continue to the Heat Index Calculator; for cold weather with wind, use the Wind Chill Calculator.
Kelvin also appears in lighting, where it describes a light source's color appearance rather than a physical temperature. That separate use is covered by the Color Temperature Converter for lighting.
Frequently asked questions
How do I convert Celsius to Fahrenheit?
Multiply the Celsius temperature by 9/5 (1.8) and then add 32. For example, 20°C × 1.8 + 32 = 68°F. To go the other way, subtract 32 and multiply by 5/9: (68 − 32) × 5/9 = 20°C.
What is absolute zero in Celsius and Fahrenheit?
Absolute zero - the lowest theoretically possible temperature - is −273.15°C or −459.67°F, which is 0 K (Kelvin) exactly. At absolute zero, the thermal motion of particles theoretically reaches its minimum. It has never been achieved in practice, though scientists have come within billionths of a degree.
At what temperature are Celsius and Fahrenheit the same?
Celsius and Fahrenheit are equal at exactly −40°. That is, −40°C = −40°F. This is the only temperature where the two scales intersect, which makes it a useful sanity check when verifying the conversion formula.
What is the difference between Kelvin and Celsius?
Kelvin and Celsius use the same degree size - a change of 1°C is exactly equal to a change of 1 K. The only difference is the zero point: Celsius is based on water's freezing point (0°C), while Kelvin is based on absolute zero (0 K = −273.15°C). To convert Celsius to Kelvin, add 273.15.
What is Rankine and when is it used?
Rankine (°R) is an absolute temperature scale that uses the Fahrenheit degree size rather than the Celsius degree size. Like Kelvin, 0°R is absolute zero. The Rankine scale is used in some branches of engineering in the United States, particularly in thermodynamics and fluid mechanics, because it allows absolute-temperature calculations using Fahrenheit-sized degrees.
How do I convert a temperature difference?
A temperature reading includes a scale offset, but a temperature difference does not. For differences, multiply a Celsius or Kelvin change by 9/5 to get Fahrenheit or Rankine; the reverse factor is 5/9. A 10°C change is a 10 K change or an 18°F change. By contrast, a reading of 10°C equals 50°F.
What is the Réaumur scale?
Réaumur (°Ré) is a historical scale where water freezes at 0°Ré and boils at 80°Ré under standard pressure. One degree Réaumur equals 1.25°C, so °C = °Ré × 5/4. It appears in some older European references and recipes; the converter includes it under the historical scale options.
Is “double Celsius and add 30” accurate?
It is a rough mental estimate for everyday weather, not an exact conversion. The shortcut doubles a Celsius value and adds 30°F; for example, 20°C gives an estimate of 70°F, while the exact result is 68°F. Use the exact formula °F = °C × 9/5 + 32 for precise work.
What is normal body temperature in Celsius and Fahrenheit?
The traditionally quoted normal human body temperature is 37°C / 98.6°F. Modern research shows that actual average body temperature is closer to 36.6°C / 97.9°F and varies by individual, time of day, and measurement site. A fever is generally defined as a core temperature above 38°C / 100.4°F.
Related tools
- Ideal Gas LawConvert to an absolute temperature before using PV = nRT.
- Specific HeatUse a temperature change with mass and specific heat to estimate energy.
- Oven Temp ConverterTranslate an oven setpoint into Celsius, Fahrenheit, or Gas Mark.
- Air Fryer ConverterAdapt a conventional oven temperature for an air fryer recipe.
- Heat Index CalculatorContinue from air temperature to a heat-index estimate that includes humidity.
- Wind Chill CalculatorEstimate wind chill from an air temperature and wind speed.