-40 Fahrenheit to Celsius
-40.0 °C
-40 °F = -40.0 °C.
Celsius
-40.0°C
-40 °F = -40.0 °C
The short answer
How many Celsius is -40 Fahrenheit?
-40 °F = -40.0 °C. 1 Fahrenheit = 0.555556 Celsius, then − 17.77777777777778, so the working is -40 × 0.555556 − 17.7778 = -40.0.
The working
The factor below is an exact definition rather than a measurement, so nothing is approximated in the arithmetic. The only rounding on this page happens where a number is displayed.
1 Fahrenheit = 0.555556 Celsius, then − 17.77777777777778 -40 × 0.555556 − 17.7778 = -40.0
How much precision do you need?
Each row is the same answer cut at a different number of decimals, with what that choice costs you. Pick the shortest row whose error is smaller than whatever you are measuring with.
| Rounded to | Answer (°C) | Off by |
|---|---|---|
| Whole number | -40 | exact |
| 1 decimal | -40.0 | exact |
| 2 decimals | -40.00 | exact |
Round trip: take -40.0 °C back the other way and you land on -40.0000 °F — a drift of 0.0000 °F. That gap is the rounding, not the conversion.
What -40 °F looks like
-40 °F
The Fahrenheit and Celsius scales meet only here, so a thermometer reading -40 gives the same answer in either unit.
Frequently asked questions
What is -40 Fahrenheit in Celsius?
-40 Fahrenheit is -40.0 Celsius. 1 Fahrenheit = 0.555556 Celsius, then − 17.77777777777778, so the working is -40 × 0.555556 − 17.7778 = -40.0.
How accurate is -40.0 °C?
Rounding to -40.0 °C and converting straight back gives -40.0000 °F, a drift of 0.0000 °F from the -40 you started with. The factor itself is exact; every bit of that difference comes from the rounding, not the conversion.
Nearby values
Any value at all
Fahrenheit to Celsius Converter
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