Can I use
?

calc() as CSS unit value

- CR

Method of allowing calculated values for length units, i.e. width: calc(100% - 3em)

IE

  1. 5.5 - 8: Not supported
  2. 9: Partial support
  3. 10: Partial support
  4. 11: Partial support

Edge

  1. 12 - 84: Supported
  2. 85: Supported

Firefox

  1. 2 - 3.6: Not supported
  2. 4 - 15: Supported
  3. 16 - 79: Supported
  4. 80: Supported
  5. 81 - 82: Supported

Chrome

  1. 4 - 18: Not supported
  2. 19 - 25: Supported
  3. 26 - 84: Supported
  4. 85: Supported
  5. 86 - 88: Supported

Safari

  1. 3.1 - 5.1: Not supported
  2. 6: Supported
  3. 6.1 - 13.1: Supported
  4. 14: Supported
  5. TP: Supported

Opera

  1. 9 - 12.1: Not supported
  2. 15 - 69: Supported
  3. 70: Supported

iOS Safari

  1. 3.2 - 5.1: Not supported
  2. 6: Supported
  3. 7 - 13.7: Supported
  4. 14.0: Supported

Opera Mini

  1. all: Not supported

Android Browser

  1. 2.1 - 4.3: Not supported
  2. 4.4 - 4.4.4: Partial support
  3. 81: Supported

Blackberry Browser

  1. 7: Not supported
  2. 10: Supported

Opera Mobile

  1. 10 - 12.1: Not supported
  2. 46: Supported

Chrome for Android

  1. 85: Supported

Firefox for Android

  1. 79: Supported

IE Mobile

  1. 10: Supported
  2. 11: Supported

UC Browser for Android

  1. 12.12: Supported

Samsung Internet

  1. 4 - 11.2: Supported
  2. 12.0: Supported

QQ Browser

  1. 10.4: Supported

Baidu Browser

  1. 7.12: Supported

KaiOS Browser

  1. 2.5: Supported

Support can be somewhat emulated in older versions of IE using the non-standard expression() syntax.

Due to the way browsers handle sub-pixel rounding differently, layouts using calc() expressions may have unexpected results.

Resources:
MDN Web Docs - calc
Mozilla Hacks article
WebPlatform Docs