Temperature Converter

Celsius to Fahrenheit, Kelvin and Rankine: a temperature converter with all four scales shown at once.

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How do you convert Celsius to Fahrenheit?

Multiply by 9/5 and add 32: 20 °C is 68 °F. The addition matters — the two scales have different zero points, not just different degree sizes, which is why 0 °C is 32 °F rather than 0 °F.

Cost: Free, no limits
Upload: None — runs on your device
Sign-up: Not required
Works offline: Yes, once loaded

How to convert Celsius to Fahrenheit

Enter the temperature
Negative values work; a temperature below absolute zero is flagged rather than converted.
Choose its scale
Celsius, Fahrenheit, Kelvin or Rankine.
Read the other scales
All of them are shown at once, with common reference points below.

Examples

100 °C212 °F · 373.15 K
Water boils at sea-level pressure.
−40 °C−40 °F
The one point where the two scales agree.
0 K−273.15 °C
Absolute zero — nothing can be colder.

Key features of the Temperature Converter

Celsius, Fahrenheit and Kelvin
Converts as you type, in every direction
Handles negative temperatures correctly
Runs entirely in your browser

Supported formats

Scales

Celsius (°C)
Fahrenheit (°F)
Kelvin (K)

When should you use this?

Converting an oven temperature from a recipe in the other system.
Reading a weather forecast given in an unfamiliar scale.
Converting a scientific measurement to or from Kelvin.

Limitations

Temperature conversion is not a simple multiplication, because Celsius and Fahrenheit have different zero points as well as different degree sizes. This is why it needs its own tool rather than a factor.
A temperature and a temperature difference convert differently. A rise of 10 °C is a rise of 18 °F, not 50 °F — the offset applies to absolute values only.
Kelvin has no degree symbol and no negative values. A negative Kelvin figure is not a cold temperature; it is an error.

Troubleshooting

A temperature difference converted to an absurd figure

You converted it as an absolute temperature. A difference scales by 9/5 with no offset: 10 °C of change is 18 °F of change.

Kelvin came out negative

The Celsius input was below −273.15, which is below absolute zero and not a physical temperature.

Common mistakes to avoid

Applying the full conversion formula to a temperature difference. The 32-degree offset does not belong there.
Writing Kelvin with a degree symbol, or reporting a negative Kelvin value.

Pro tips

Tips for better results

Mental maths
Double it and add 30 gets you close
For a rough mental Celsius-to-Fahrenheit conversion, double it and add 30. It is within a few degrees across normal weather.
Differences
Converting a change uses 9/5 without the offset
When converting a change in temperature rather than a temperature, use the ratio 9/5 alone and ignore the offset.

Standards and terms behind the Temperature Converter

The named things this tool works with, and the documents that define them.

SI unitsSpecification: The international system of units, maintained by the BIPM, which fixes the metre, kilogram, second and kelvin. Reference: SI units
Imperial and US customary unitsSpecification: Inches, feet, pounds, gallons and Fahrenheit — still standard in the United States and common in the UK.

Also searched as: celsius to fahrenheit formula, oven temperature conversion, kelvin to celsius.

Why temperature is different from other units

Most unit conversions are a single multiplication: metres to feet, grams to ounces. Temperature is not, because Celsius and Fahrenheit have different zero points as well as different degree sizes.

0 °C is 32 °F, not 0 °F. So converting requires both an offset and a scale factor: °F = °C × 9/5 + 32. Treating temperature as a simple factor — which some converters do — produces the classic error of reporting 0 °C as 0 °F.

Absolute scales

Kelvin and Rankine start at absolute zero, the point where thermal motion is minimal. Because their zero is a physical floor rather than an arbitrary reference, they do scale multiplicatively — 200 K really is twice as hot as 100 K, while 20 °C is not twice as hot as 10 °C.

Kelvin uses Celsius-sized degrees (and takes no degree symbol: it is "300 K", not "300 °K"). Rankine uses Fahrenheit-sized degrees and turns up mostly in American engineering.

The −40 crossover

−40 °C and −40 °F are the same temperature — the one point where the two scales meet. It is a useful sanity check on any conversion: if a converter does not agree at −40, it is wrong.

Privacy

The Temperature Converter runs entirely in your browser. What you enter and the result it produces stay on your own device — nothing is sent anywhere, because nothing needs to be.

You can confirm this rather than take our word for it: open your browser’s developer tools, watch the Network tab, and use the tool. No request carries your input. It also keeps working with the connection off.

Details are in the privacy policy.

What next?

Length, weight, volume, area, speed and data size.

Other unit converters

Temperature Converter — questions

How do I convert Kelvin to Celsius?

Subtract 273.15: 300 K is 26.85 °C. For Celsius to Kelvin, add 273.15. A kelvin and a degree Celsius are the same size; only the zero point differs.

How do I convert Celsius to Fahrenheit?

Multiply by 9/5 and add 32. For 20 °C: 20 × 1.8 + 32 = 68 °F. The addition matters — the two scales have different zero points, not just different degree sizes.

How do I convert Fahrenheit to Celsius?

Subtract 32, then multiply by 5/9. For 98.6 °F: (98.6 − 32) × 5/9 = 37 °C.

At what temperature are Celsius and Fahrenheit equal?

−40. It is the single crossover point of the two scales, and a good check on any converter: if it disagrees at −40, it is wrong.

Why does Kelvin not use a degree symbol?

Because it is an absolute scale, not a relative one. The unit is the kelvin, written "300 K" — never "300 °K". Kelvin degrees are the same size as Celsius degrees, offset by 273.15.

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