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rem (root em) units

Type of unit similar to em, but relative only to the root element, not any parent element. Thus compounding does not occur as it does with em units.

Spec https://www.w3.org/TR/css3-values/#font-relative-lengths
Status W3C Candidate Recommendation
IE Edge Firefox Chrome Safari Opera
      73    
    65 72    
    64 71 TP  
11 18 63 70 12 56
10 (1) 17 62 69 11.1 55
9 (1) 16 61 68 11 54
8 15 60 67 10.1 53
Show all
7 14 59 66 10 52
6 13 58 65 9.1 51
5.5 12 57 64 9 50
    56 63 8 49
    55 62 7.1 48
    54 61 7 47
    53 60 6.1 46
    52 59 6 45
    51 58 5.1 44
    50 57 5 43
    49 56 4 42
    48 55 3.2 41
    47 54 3.1 40
    46 53   39
    45 52   38
    44 51   37
    43 50   36
    42 49   35
    41 48   34
    40 47   33
    39 46   32
    38 45   31
    37 44   30
    36 43   29
    35 42   28
    34 41   27
    33 40   26
    32 39   25
    31 38   24
    30 37   23
    29 36   22
    28 35   21
    27 34   20
    26 33   19
    25 32   18
    24 31   17
    23 30   16
    22 29   15
    21 28   12.1
    20 27   12
    19 26   11.6
    18 25   11.5
    17 24   11.1
    16 23   11
    15 22   10.6
    14 21   10.5
    13 20   10.0-10.1
    12 19   9.5-9.6
    11 18   9
    10 17    
    9 16    
    8 15    
    7 14    
    6 13    
    5 12    
    4 11    
    3.6 10    
    3.5 9    
    3 8    
    2 7    
      6    
      5    
      4    
iOS Safari Opera Mini Android Browser Blackberry Browser Opera Mobile Android Chrome Android Firefox IE Mobile Android UC Browser Samsung Internet QQ Browser Baidu Browser
12 all 67 10 46 70 63 11 11.8 7.2 1.2 7.12
11.3-11.4   4.4.3-4.4.4 7 12.1     10   6.2    
11.0-11.2   4.4   12         5    
10.3   4.2-4.3   11.5         4    
Show all
10.0-10.2   4.1   11.1              
9.3   4   11              
9.0-9.2   3   10              
8.1-8.4   2.3                  
8   2.2                  
7.0-7.1   2.1                  
6.0-6.1                      
5.0-5.1 (2)                      
4.2-4.3                      
4.0-4.1                      
3.2                      

Notes

  1. IE 9 & IE 10 do not support rem units when used in the font shorthand property (the entire declaration is ignored) or when used on pseudo elements.

  2. iOS Safari 5.0-5.1 support rem but not in combination with media queries.

Bugs

  • IE 9, 10 and 11 do not support rem units when used in the "line-height" property when used on :before and :after pseudo elements (https://connect.microsoft.com/IE/feedback/details/776744).

  • Borders sized in "rem" disappear when the page is zoomed out in Chrome.

  • Reportedly does not work on Android 4.3 browser for Samsung Note II or the Samsung Galaxy Tab 2 on Android 4.2.

  • Chrome 31-34 & Chrome-based Android versions (like 4.4) have a font size bug that occurs when the root element has a percentage-based size.

  • Causes content display and scrolling issues on iPhone 4 which typically has Safari 5.1.

Resources

Data by caniuse.com
Licensed under the Creative Commons Attribution License v4.0.
http://caniuse.com/#feat=rem