Temperature conversion

Fahrenheit to Celsius Calculator

Convert a Fahrenheit temperature reading to Celsius by subtracting 32 and multiplying by 5/9.

Temperature input

Enter a temperature in Fahrenheit

°F → °C

Temperature in Fahrenheit (°F)

Converted temperature

Celsius reading

The converted temperature will appear here

Enter any finite Fahrenheit reading, including negative values.

What is Fahrenheit To Celsius ?

The Fahrenheit to Celsius converter changes a temperature reading from the scale commonly used in the United States to the scale used for weather, cooking, medicine and science in most of the world. It is handy when a forecast says 86 °F but a travel guide discusses 30 °C, or when an appliance manual and a recipe use different scales.

Temperature scales are not converted like ordinary lengths or weights because their zero points are different. A correct conversion first removes the Fahrenheit offset and then changes the size of each degree. This page handles both steps and reports the Celsius value to two decimal places when needed.

How to Use This Calculator

Enter the temperature as a Fahrenheit number. Decimal values and temperatures below zero are allowed.
Select Calculate. The converter subtracts 32, multiplies the remainder by 5, and divides by 9.
Read the answer in degrees Celsius (°C). Use Reset before starting a separate conversion.

The order matters. Subtracting 32 accounts for the fact that water freezes at 32 °F but 0 °C. Multiplying by 5/9 then accounts for the different degree sizes: an interval of 9 Fahrenheit degrees covers the same temperature change as 5 Celsius degrees.

For a quick mental estimate in everyday weather, subtract 30 and halve the result. For example, 70 °F becomes roughly 20 °C. That shortcut is convenient but is not exact; the calculator should be used when accuracy matters.

Formula Used

Celsius = (Fahrenheit − 32) × 5/9

The parentheses show that 32 must be subtracted before multiplication. The fraction 5/9 is exact for converting a temperature reading under the definitions of these scales. Another equivalent form is Celsius = (Fahrenheit − 32) ÷ 1.8. The calculator rounds the result to two decimal places.

For temperature differences, the zero-point adjustment is omitted. A rise of 18 °F is a rise of 10 °C because 18 × 5/9 = 10. That is different from converting a thermometer reading of 18 °F, which is about −7.78 °C.

Variables Explained

Symbols and values used in the Fahrenheit-to-Celsius conversion
Symbol or value	Meaning	Unit
°F	The Fahrenheit temperature entered in the form	degrees Fahrenheit
°C	The converted temperature on the Celsius scale	degrees Celsius
32	The Fahrenheit reading at the freezing point of water under standard reference conditions, corresponding to 0 °C	degrees Fahrenheit
5/9	The exact ratio between the size of a Celsius degree and a Fahrenheit degree	dimensionless scale factor

The degree symbol belongs with both Fahrenheit and Celsius values. A negative sign describes a reading below that scale’s zero point; it does not mean the temperature is physically impossible. Celsius can extend down to absolute zero, approximately −273.15 °C.

Worked Example

Suppose a weather report lists an afternoon temperature of 77 °F. Substitute 77 into the formula:

Remove the offset: 77 − 32 = 45.
Apply the scale factor: 45 × 5/9 = 25.
State the converted reading: 77 °F = 25 °C.

As a second check, consider 14 °F. The calculation is (14 − 32) × 5/9 = −18 × 5/9 = −10 °C. This example shows why the subtraction must happen first. Multiplying 14 by 5/9 before handling the offset would produce the wrong answer.

The converter rounds its displayed result to two decimal places. Entering 100 °F gives 37.78 °C after rounding, while the unrounded value continues as 37.777…. For ordinary weather comparisons, a whole degree may be enough; laboratory work should follow the precision of the original measurement and the needs of the procedure.

Why Use This Calculator?

The result represents the same physical temperature on another numbered scale. Nothing has become warmer or cooler during the conversion. Familiar reference points help put the answer in context: 32 °F equals 0 °C, 68 °F equals 20 °C, 77 °F equals 25 °C, and 212 °F equals 100 °C at standard atmospheric pressure.

A converted number should not imply more measurement accuracy than the input. If an outdoor thermometer reads 73 °F only to the nearest degree, 22.78 °C is the mathematical conversion, but reporting about 23 °C better reflects the measurement. Extra decimal places can be useful during intermediate work; round after the calculation rather than rounding each step.

Boiling and freezing points vary with pressure and, for mixtures, composition. The scale conversion itself remains valid, but a familiar benchmark such as water boiling at 100 °C assumes specified conditions. For safety limits, medical decisions, industrial controls or calibrated scientific observations, follow the instrument and procedure requirements rather than relying only on a rounded web result.

Common Mistakes

Skipping the offset: multiplying °F by 5/9 alone converts a temperature interval, not an actual reading.
Using 9/5: that factor belongs in the reverse Celsius-to-Fahrenheit direction.
Changing the order: calculate °F − 32 first. Written parentheses are there to prevent ambiguity.
Confusing a reading with a change: 18 °F is about −7.78 °C, but an increase of 18 Fahrenheit degrees equals an increase of 10 Celsius degrees.
Dropping the unit: a bare “20” does not tell a reader which scale was used.
Rounding too early: keep the full intermediate value and round the final result to a sensible precision.
Using a familiar phase point as a universal constant: the boiling point of water changes with atmospheric pressure.

If a result seems surprising, test the formula at 32 °F. It should return exactly 0 °C. Testing 212 °F should return 100 °C. These two reference conversions catch most reversed factors and missing offsets.

Frequently Asked Questions

What is 100 °F in Celsius?

Using (100 − 32) × 5/9 gives 37.777…, so 100 °F is approximately 37.78 °C. Whether that represents a fever depends on where and how body temperature was measured; use appropriate medical guidance for health decisions.

At what temperature are Fahrenheit and Celsius equal?

The two scales show the same number at −40. Substituting −40 into the formula gives (−40 − 32) × 5/9 = −40, so −40 °F equals −40 °C.

Why does the formula subtract 32?

Fahrenheit and Celsius place zero at different temperatures. Water’s standard freezing reference is 32 °F and 0 °C, so subtracting 32 aligns the starting points before the degree-size conversion.

Can I enter a negative Fahrenheit temperature?

Yes. Negative Fahrenheit readings are valid. For example, −4 °F converts to −20 °C. Include the minus sign with the number and do not treat it as a subtraction instruction.

How do I estimate Fahrenheit to Celsius without a calculator?

For a rough weather estimate, subtract 30 and divide by 2. It makes 86 °F about 28 °C instead of the exact 30 °C, so use the full formula when precision matters.

Is one Fahrenheit degree the same size as one Celsius degree?

No. A Celsius degree spans 9/5, or 1.8, Fahrenheit degrees. That is why a 10 °C temperature increase corresponds to an 18 °F increase.

Should converted temperatures keep two decimal places?

Two decimals are useful for showing the mathematical result, but the final precision should match the original reading. A whole-degree weather observation generally should not become a supposedly exact hundredth-degree measurement after conversion.