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One letter apart, and the two scales agree at exactly one temperature in the whole range.
Check the letter after the degree sign. C is Celsius, on which water freezes at 0 and boils at 100. F is Fahrenheit, on which the same points are 32 and 212. The scales coincide at −40 and nowhere else, so a number without its letter is genuinely ambiguous — and at everyday temperatures the same figure means very different weather.
Identical in construction and different in scale; a number without its letter is ambiguous and sometimes dangerously so.
| Degree Celsius symbol | Degree Fahrenheit symbol | |
|---|---|---|
| Water freezes at | 0 °C | 32 °F |
| Water boils at | 100 °C | 212 °F |
| Is it an SI unit? | Accepted for use with the SI, and defined by the BIPM | No. The SI does not define it; NIST treats it as customary |
| Where it is used | Most of the world, and all scientific work | The United States and a few other jurisdictions |
| They agree at | −40 °C | −40 °F — the only coincident point |
| Relationship (from Symbolwise's records) | Commonly confused with Degree Fahrenheit symbol — Identical in construction and different in scale; a number without its letter is ambiguous and sometimes dangerously so. | Commonly confused with Degree Celsius symbol — One letter apart, and the scales agree at only one temperature. |
The International System of Units (SI), 9th edition
Bureau International des Poids et Mesures · retrieved 2026-07-31
The defining document for SI unit names and symbols, including the capitalisation and spacing rules. It defines units; it says nothing about how a symbol is encoded in a character set, and nothing about non-SI units except where it lists those accepted for use with the SI.
Wikipedia · retrieved 2026-07-31
Tertiary reference. Used for origin narrative and for units the SI does not define, never for an official-definition claim.
Wikipedia · retrieved 2026-07-31
Tertiary reference. Used for origin narrative and for units the SI does not define, never for an official-definition claim.
A change of one kelvin and a change of one degree Celsius are exactly the same size, so a temperature *difference* may be stated in either. The scales start in different places: 0 K is absolute zero and 0 °C is the freezing point of water, 273.15 K. The written forms differ too — the kelvin takes no degree sign, so 300 K is right and 300 °K is not.
The degree sign is the discriminator, and it is the thing plain text loses. °C is a temperature and needs its preceding degree sign and a space before the number; italic c is a speed and stands alone in an equation. Where formatting is stripped — a filename, a search box, a plain-text note — they become indistinguishable.
Look for the horizontal line. Fire is a plain upward triangle; air is the same triangle with a bar drawn across its upper part. Dropping the bar is the commonest error in reproductions of the element set, and it turns air into fire.
The same rule as fire and air, inverted. Water is a plain downward triangle; earth is the same triangle with a bar across its lower part. The four element signs are one designed set: two point up, two point down, and within each pair the bar is the only difference.