Fahrenheit to Celsius Converter
Convert between any two temperature scales: Fahrenheit, Celsius, Kelvin, and Rankine. Enter a value, pick your "from" and "to" scales, and get the exact result with a full show-your-work breakdown. The default converts 98.6 °F (normal body temperature) to Celsius.
Formula
Worked example
Body temperature of 98.6 °F: C = (98.6 - 32) x 5/9 = 66.6 x 5/9 = 37 °C. Then K = 37 + 273.15 = 310.15 K, and R = 310.15 x 9/5 = 558.27 °R.
How the Fahrenheit to Celsius formula works
The Fahrenheit and Celsius scales place their zero points in different spots and divide the gap between freezing and boiling water into a different number of steps, so converting between them takes two operations. First you subtract 32 to align the freezing point of water, which sits at 32 °F but at 0 °C. Then you multiply by 5/9 because the 180 Fahrenheit degrees between freezing and boiling correspond to only 100 Celsius degrees, and 100/180 reduces to 5/9. Doing the subtraction before the multiplication is essential because reversing the order gives the wrong answer. To go the other direction from Celsius to Fahrenheit, you reverse both steps: multiply by 9/5 first, then add 32.
Kelvin and Rankine: the absolute temperature scales
Kelvin and Rankine are absolute scales, meaning their zero point is absolute zero, the coldest possible temperature where all thermal motion stops. Kelvin uses the same degree size as Celsius, so converting from Celsius is simply adding 273.15. Rankine uses the same degree size as Fahrenheit, so converting from Fahrenheit is adding 459.67, or equivalently converting to Celsius first and then multiplying (C + 273.15) by 9/5. Scientists and engineers use Kelvin for thermodynamics equations; Rankine appears in some US engineering contexts. A quick sanity check: water freezes at 273.15 K (491.67 °R) and boils at 373.15 K (671.67 °R).
All four scale conversions in one table
This converter handles all four temperature scales in a single step. Enter a value in any scale, choose your target, and get the exact result. Every conversion routes through Celsius as the intermediate step. The show-your-work panel below the result shows each arithmetic step with your actual numbers substituted in, so you can verify the answer by hand or in a spreadsheet. The all-scales summary at the bottom of the steps panel shows the equivalent temperature in every scale at once.
Quick estimation tricks
When you need a rough Fahrenheit-to-Celsius figure in your head, subtract 30 and halve the result. For 70 °F this gives 20 °C, close to the exact 21.1 °C. Going from Celsius to Fahrenheit, double and add 30 for an estimate. These tricks are accurate to within a few degrees in everyday temperature ranges. For anything precise, use the exact formula or the calculator above. The two scales read identically at exactly -40 degrees, the only crossing point because their relationship is a straight line with a non-zero intercept.
Common temperature conversions across all four scales
| Description | Fahrenheit (°F) | Celsius (°C) | Kelvin (K) | Rankine (°R) |
|---|---|---|---|---|
| Absolute zero | -459.67 | -273.15 | 0 | 0 |
| Dry ice (CO2 sublimation) | -109.3 | -78.5 | 194.65 | 350.37 |
| Mercury freezes | -37.89 | -38.83 | 234.32 | 421.78 |
| Salt-water freezes (avg) | 26.6 | -3 | 270.15 | 486.27 |
| Fresh water freezes | 32 | 0 | 273.15 | 491.67 |
| Room temperature | 68 | 20 | 293.15 | 527.67 |
| Normal body temperature | 98.6 | 37 | 310.15 | 558.27 |
| Fever threshold | 100.4 | 38 | 311.15 | 560.07 |
| Water boils (sea level) | 212 | 100 | 373.15 | 671.67 |
| Oven moderate heat | 350 | 176.67 | 449.82 | 809.67 |
All values rounded to two decimal places. Sorted from coldest to hottest.
Frequently asked questions
What is the formula to convert Fahrenheit to Celsius?
Use C = (F - 32) x 5/9. Subtract 32 from the Fahrenheit temperature to align the freezing point, then multiply by 5/9 to scale the degree size. For example, 50 °F gives (50 - 32) x 5/9 = 18 x 5/9 = 10 °C.
How do I convert Celsius back to Fahrenheit?
Reverse the steps: F = C x 9/5 + 32. Multiply the Celsius value by 9/5 (or 1.8) first, then add 32. For example, 100 °C gives 100 x 9/5 + 32 = 180 + 32 = 212 °F.
What is the difference between Kelvin and Celsius?
Kelvin and Celsius have identical degree sizes, so a temperature change of 1 °C is always the same as a change of 1 K. The only difference is the zero point: Celsius puts zero at the freezing point of water, while Kelvin puts zero at absolute zero (-273.15 °C). To convert, add or subtract 273.15.
What is Rankine and when is it used?
Rankine is an absolute temperature scale that uses Fahrenheit-sized degrees. Its zero is absolute zero (same as Kelvin) but its degrees are larger by the factor 9/5. Rankine appears in some US engineering and thermodynamics contexts where calculations need an absolute scale but practitioners work in Fahrenheit units.
At what temperature do Fahrenheit and Celsius read the same?
They meet at exactly -40 degrees: -40 °F = -40 °C. This is the only crossing point because the Fahrenheit-to-Celsius relationship is a straight line (C = (F - 32) x 5/9) that crosses the line C = F at precisely that value.
Is there a quick way to estimate the conversion in my head?
For a rough Fahrenheit-to-Celsius figure, subtract 30 and halve the result: (F - 30) / 2. For 70 °F this gives about 20 °C (exact is 21.1 °C). Going the other way, double the Celsius value and add 30 for an estimate of Fahrenheit. These are fast mental shortcuts; use the exact formula for accuracy.
What is absolute zero in Fahrenheit, Celsius, and Kelvin?
Absolute zero is the lowest possible temperature. It equals 0 K = -273.15 °C = -459.67 °F = 0 °R. At this point, all classical thermal motion ceases. No physical object can reach absolute zero, though scientists have cooled matter to within fractions of a nanokelvin of it.