Fahrenheit to Celsius Calculator

About the Fahrenheit to Celsius Calculator

American weather reports, oven dials, cookbooks, fever thermometers and car dashboards show temperatures in Fahrenheit, while the rest of the world, and all of science, uses Celsius. Converting Fahrenheit to Celsius is needed when following an American recipe, understanding a US forecast, checking a child's temperature on an imported thermometer, or answering a homework question.

This Fahrenheit to Celsius calculator converts °F to °C exactly and shows each step of the formula. It also gives the temperature in kelvin, compares the exact result with the subtract-30-and-halve estimate, and describes what the temperature means.

How to Use the Fahrenheit to Celsius Calculator

Enter the temperature in degrees Fahrenheit. Negative values are fine, down to absolute zero at −459.67 °F.

The Celsius value appears straight away with the working shown.

The Formula

  °C = (°F − 32) × 5/9
     = (°F − 32) ÷ 1.8

Subtract 32 first, to measure from the freezing point of water, then multiply by 5/9 to turn the smaller Fahrenheit degrees into larger Celsius ones. The order matters: multiplying first and subtracting afterwards gives a different, wrong answer.

Step-by-Step Example

98.6 °F, normal body temperature.

  − 32:    98.6 − 32 = 66.6
  × 5/9:   66.6 × 5/9 = 37 °C

350 °F, the standard American baking temperature.

  350 − 32 = 318
  318 × 5/9 = 176.667 °C

Oven dials in Celsius are marked in steps of 10 or 20, so this is usually set at 175 or 180 °C.

0 °F, a very cold winter day.

  0 − 32 = −32
  −32 × 5/9 = −17.7778 °C

Weather Temperatures

    0 °F  =  −17.8 °C       60 °F  =  15.6 °C
   20 °F  =   −6.7 °C       70 °F  =  21.1 °C
   32 °F  =    0 °C         80 °F  =  26.7 °C
   40 °F  =    4.4 °C       90 °F  =  32.2 °C
   50 °F  =   10 °C        100 °F  =  37.8 °C

The Subtract-30-and-Halve Shortcut

A quick mental method is to take 30 away and halve the result. At 50 °F it is exact: (50 − 30) ÷ 2 = 10 °C. It stays within a few degrees for everyday weather between about 30 and 80 °F, but drifts for anything hotter or colder: at 350 °F it gives 160 °C instead of 176.7, and at 98.6 °F it gives 34.3 °C instead of 37, which could hide a fever. Use the exact formula for cooking and health.

American Oven Settings

  250 °F  =  121 °C          375 °F  =  191 °C
  300 °F  =  149 °C          400 °F  =  204 °C
  325 °F  =  163 °C          425 °F  =  218 °C
  350 °F  =  177 °C          450 °F  =  232 °C

For a fan oven, reduce the converted Celsius figure by about 20 degrees, since fan ovens cook more quickly.

Fevers and Health

Fever thresholds are usually given in both scales: 100.4 °F is 38 °C, and 102 °F is about 38.9 °C. Many digital thermometers can switch scales, but if yours cannot, convert carefully — a difference of one degree Fahrenheit is just over half a degree Celsius, so small readings matter.

Room and Thermostat Settings

Indoor comfort is usually between about 68 and 72 °F, which is 20 to 22 °C. A thermostat setting of 65 °F is 18.3 °C, and 75 °F is 23.9 °C. Each degree Fahrenheit turned down is about 0.56 °C, which is why energy-saving advice in the US suggests lowering the thermostat by several degrees at a time.

Where Fahrenheit Came From

Daniel Gabriel Fahrenheit, a German-born instrument maker working in the Netherlands, proposed his scale in 1724. He set 0 °F at the temperature of a mixture of ice, water and salt, the coldest he could reliably reproduce, and placed human body temperature near 96 °F. Later adjustments fixed the freezing and boiling points of water at 32 °F and 212 °F, which moved normal body temperature to about 98.6 °F. Anders Celsius's scale of 1742, reversed soon after his death so that 0 was freezing and 100 boiling, became the basis of the metric system and is now used almost everywhere.

Converting in Your Head More Accurately

If the quick estimate is not close enough, a slightly better method is to subtract 32, halve the result, and then add a tenth of that half. For 80 °F: 80 − 32 = 48, half is 24, plus 2.4 gives 26.4 °C, against the exact 26.7. The extra step corrects most of the error in simply halving, since 5/9 is about 0.556, a little more than a half, and it works at any temperature.

Scientific Work

Laboratory results, chemistry problems and physics textbooks use Celsius or kelvin, never Fahrenheit. When data arrives in Fahrenheit — from an American instrument, a historical weather record or a US engineering specification — convert it to Celsius first, then add 273.15 if the calculation needs kelvin. Keep full precision during the conversion and round only the final answer, since rounding each step can shift a result by a tenth of a degree or more.

Understanding Your Result

The headline is the temperature in degrees Celsius.

The kelvin line gives the scientific temperature, °C + 273.15.

The quick estimate line shows the subtract-30-and-halve answer and how far off it is.

The what it means line describes the temperature in everyday terms.

When Should You Use This Calculator?

Use it for American recipes and oven settings.

Use it for US weather forecasts and travel.

Use it for body temperatures and fevers read in Fahrenheit.

Use it for science homework that asks for Celsius or kelvin.

Common Mistakes

Multiplying before subtracting 32. Always subtract 32 first.

Using 9/5 instead of 5/9. Fahrenheit to Celsius uses 5/9.

Using the shortcut for fevers. It can be several degrees out.

Subtracting 32 from a temperature change. A change of 18 °F is a change of 10 °C.

Rounding oven temperatures the wrong way. Round to the nearest mark on your dial, not always down.