How do you strip the unit from any number in SASS?

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UPDATE: You should never actually need to use this function. Sass math is very smart about units, and I have never seen a use-case in which stripping units was a better option than simply using correct math to get what you need. See the Sass issue thread where this has been discussed at length.

It's a clever function, but if you ever feel like using it, there's probably a problem with your math. Don't fall back on this function. Fix your math instead.

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You need to divide by 1 of the same unit. If you use unit(), you get a string instead of a number, but if you multiply by zero and add 1, you have what you need:

@function strip-units($number) {
  @return $number / ($number * 0 + 1);
}

UPDATE: In the latest versions of Sass, that becomes:

@use 'sass:math';

@function strip-units($number) {
  @return math.div($number, ($number * 0 + 1));
}

That works. strip-units(13.48cm) will return 13.48.