The calc() CSS function can be used anywhere a <length>, <frequency>, <angle>, <time>, <number>, or <integer> is required. With calc(), you can perform calculations to determine CSS property values.

It is possible to use calc() inside another calc().

[Webplatform](docs.webplatform.org/wiki/css/functions/calc "Webplatform")
[Mozilla docs](https://developer.mozilla.org/en-US/docs/Web/CSS/calc "Mozilla")
[Caniuse](http://caniuse.com/#feat=calc "Caniuse")