Converting units

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Converting a quantity means writing the same amount in a different unit: five kilometres as miles, a hundred centimetres as metres, a temperature in Celsius as Fahrenheit. The amount does not change, only the unit it is expressed in.

to, in and into all convert.

5 km to miles // 3.11 miles
100 cm into m // 1.00 m
1 hour to minutes // 60 minutes
72F to C // 22.22 C
20C in F // 68.00 F

A conversion between two different dimensions has no answer, so it is refused rather than guessed. The message names the dimensions rather than the units, so 1 hour in metres reports a duration cannot be converted to a length and 5 kg in m reports a mass cannot be converted to a length. Combining two different dimensions is refused the same way: 5 kg + 3 m reports mass and length cannot be added.

Temperatures, with or without the degree sign

°C and °F read as the units they obviously are, which is what a phone keyboard, a weather app and a recipe all write. The precomposed ℃ and ℉ that some keyboards emit read the same way, and °K is kelvin, which has no degree sign of its own.

20°C in F // 68.00 F
100°F in C // 37.78 C
180°C in gas mark // gas 4
37°C // 37.00 °C

The scale letter is what makes it a temperature, so the bare symbol is still an angle:

90° // 90.00 degrees

Every spelling of the same question agrees, so use whichever you have to hand:

20 C in F // 68.00 F
20 degrees C in F // 68.00 F
20° C in F // 68.00 F

The boundary is the symbol forms only. C is Celsius, and no ordinary word is claimed as a unit: the cooking cup is spelled cup, not c, which is not a unit at all. The case sensitivity of the unit table is unchanged.

1 cup in ml // 236.59 ml

Inches, where the abbreviation is also the word for converting

in is how the engine spells the conversion itself, so it cannot simply be a unit as well: 12 in ft has to keep meaning “twelve, in feet”. The word is read as inches where there is plainly nothing to convert into, which is at the end of a line, before an operator, or before a second in or a to.

12 in in cm // 30.48 cm
2 in + 3 in // 5.00 in
12 in to cm // 30.48 cm

Everywhere else it is still the preposition, including when the thing being converted into is itself inches:

3 ft in in // 36.00 in

The full spellings never have to be reasoned about at all, so they are the safer thing to write in a document somebody else will read:

12 inches in cm // 30.48 cm
1 inch in mm // 25.40 mm