Metric Temperature Conversion Calculator

A metric temperature conversion calculator converts a temperature between Celsius and Fahrenheit, the scales most commonly used in everyday weather, cooking, and household information. Enter a value in either scale to get its equivalent in the other; the formulas also explain why temperature conversions require both multiplication and an offset.

Formula

To convert Celsius to Fahrenheit, multiply the Celsius temperature by 9/5 and add 32. To convert Fahrenheit to Celsius, subtract 32 from the Fahrenheit temperature and multiply the result by 5/9.

• C is temperature in degrees Celsius (°C).
• F is temperature in degrees Fahrenheit (°F).

The formulas are F = C × 9/5 + 32 and C = (F − 32) × 5/9. The calculator displays each result to one decimal place. A displayed value is rounded for readability; calculations should use the unrounded value when greater precision matters.

Worked Example

Using the default Celsius input of 20 °C:

1. Multiply by 9/5: 20 × 9/5 = 36.
2. Add 32: 36 + 32 = 68 °F.

Using the default Fahrenheit input of 68 °F:

1. Subtract 32: 68 − 32 = 36.
2. Multiply by 5/9: 36 × 5/9 = 20 °C.

The calculator therefore returns 68.0 °F and 20.0 °C for its respective default inputs. They are two separate conversions: change the input value in the scale you want to convert, then read that scale’s output.

When to Use a Temperature Converter

Celsius is the standard temperature scale in the metric system and is used for most weather reports and everyday measurements around the world. Fahrenheit remains common in everyday use in the United States. Conversion is useful when comparing a forecast from another country, following a recipe written for a different audience, or interpreting a thermometer or appliance display.

For a quick mental estimate, double a Celsius value and add 30 to approximate Fahrenheit. For example, 20 °C becomes roughly 70 °F by this shortcut, close to the exact 68 °F. It is only an estimate, not a substitute for the formula when precision matters. The reverse shortcut—subtract 30 and halve—can roughly estimate Celsius from Fahrenheit, but also loses accuracy.

Understanding the Scales

Celsius and Fahrenheit use different sized degrees and different zero points. Water freezes at 0 °C, equivalent to 32 °F, and boils at 100 °C, equivalent to 212 °F, at standard atmospheric pressure. Between those two reference points, 100 Celsius degrees cover the same temperature interval as 180 Fahrenheit degrees. Consequently, one Celsius degree corresponds to 1.8 Fahrenheit degrees.

The conversion has an offset because the scales do not share a zero. Multiplying by 9/5 adjusts the size of the interval; adding 32 shifts the zero point. This is why simply multiplying a Celsius value by 1.8 does not produce the correct Fahrenheit temperature. The two scales agree at −40 degrees: −40 °C equals −40 °F.

Kelvin is another temperature scale used widely in science. A temperature in kelvins is related to Celsius by K = °C + 273.15. Kelvin has the same interval size as Celsius but starts at absolute zero; its unit is called the kelvin, symbol K, and is written without a degree sign. This calculator handles Celsius and Fahrenheit, so convert through Celsius if you need a Kelvin value.

Common Conversion Mistakes and Limits

• Leaving out the offset: Celsius-to-Fahrenheit conversion requires adding 32 after multiplying. Fahrenheit-to-Celsius conversion requires subtracting 32 first.
• Using the wrong factor: Celsius-to-Fahrenheit uses 9/5; Fahrenheit-to-Celsius uses 5/9.
• Mixing up temperature and temperature differences: For a change in temperature, the offset does not apply. A rise of 10 °C is a rise of 18 °F, not 50 °F.
• Rounding too early: Keep full precision through intermediate steps, then round the final display. Small differences may arise when comparing rounded results.

The formulas convert a temperature reading; they do not account for measurement error, calibration, or conditions affecting a real thermometer. They also do not determine whether a particular temperature is appropriate for a process. For cooking, laboratory work, equipment limits, or other tasks where exact requirements matter, consult the relevant instructions and use a suitable, correctly calibrated instrument.

Frequently Asked Questions

How do I convert Celsius to Fahrenheit?
Multiply the Celsius temperature by 9/5, then add 32. For example, 25 °C × 9/5 + 32 = 77 °F.

How do I convert Fahrenheit to Celsius?
Subtract 32 from the Fahrenheit temperature, then multiply by 5/9. For example, (77 °F − 32) × 5/9 = 25 °C.

What is 20 °C in Fahrenheit?
20 °C equals 68 °F, using 20 × 9/5 + 32.

At what temperature are Celsius and Fahrenheit equal?
The scales show the same number at −40: −40 °C = −40 °F.

Is a Celsius degree the same size as a Fahrenheit degree?
No. A change of 1 °C equals a change of 1.8 °F. Celsius and Fahrenheit also have different zero points.

How do I convert Celsius to Kelvin?
Add 273.15 to the Celsius temperature: K = °C + 273.15. Kelvin values use K, not °K.

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in c | Celsius temperature | °C | 20
in f | Fahrenheit temperature | °F | 68
out fahrenheit | Fahrenheit | °F | c * 9 / 5 + 32 | 1
out celsius | Celsius | °C | (f - 32) * 5 / 9 | 1