diff --git a/scss/_reboot.scss b/scss/_reboot.scss
index 34527010ae9aa9a1b48679d821444b57d060530d..e0d4f498a53c120db795e3deed92967e6f944b05 100644
--- a/scss/_reboot.scss
+++ b/scss/_reboot.scss
@@ -213,7 +213,7 @@ small {
 sub,
 sup {
   position: relative;
-  @include font-size(75%);
+  @include font-size($sub-sup-font-size);
   line-height: 0;
   vertical-align: baseline;
 }
@@ -298,7 +298,7 @@ kbd {
 
   kbd {
     padding: 0;
-    @include font-size(100%);
+    @include font-size(1em);
     font-weight: $nested-kbd-font-weight;
   }
 }
diff --git a/scss/_type.scss b/scss/_type.scss
index 0e266e55794a592a1bfd5c4a6a93c5aae4af58e6..7726b7b212c6e5c1693cb666d267f04011924f9a 100644
--- a/scss/_type.scss
+++ b/scss/_type.scss
@@ -91,7 +91,7 @@
 
 // Builds on `abbr`
 .initialism {
-  @include font-size(90%);
+  @include font-size($initialism-font-size);
   text-transform: uppercase;
 }
 
diff --git a/scss/_variables.scss b/scss/_variables.scss
index 15559e682dacd5c17bc47668f7e4d547fe136bb1..ed2755901d00bae09a0285aeefa157c2e7588d62 100644
--- a/scss/_variables.scss
+++ b/scss/_variables.scss
@@ -332,10 +332,14 @@ $display-line-height:         $headings-line-height !default;
 $lead-font-size:              $font-size-base * 1.25 !default;
 $lead-font-weight:            300 !default;
 
-$small-font-size:             80% !default;
+$small-font-size:             .875em !default;
+
+$sub-sup-font-size:           .75em !default;
 
 $text-muted:                  $gray-600 !default;
 
+$initialism-font-size:        $small-font-size !default;
+
 $blockquote-small-color:      $gray-600 !default;
 $blockquote-small-font-size:  $small-font-size !default;
 $blockquote-font-size:        $font-size-base * 1.25 !default;
@@ -923,7 +927,7 @@ $toast-header-border-color:         rgba(0, 0, 0, .05) !default;
 
 // Badges
 
-$badge-font-size:                   75% !default;
+$badge-font-size:                   .75em !default;
 $badge-font-weight:                 $font-weight-bold !default;
 $badge-color:                       $white !default;
 $badge-padding-y:                   .25em !default;
@@ -1040,7 +1044,7 @@ $thumbnail-box-shadow:              $box-shadow-sm !default;
 
 // Figures
 
-$figure-caption-font-size:          90% !default;
+$figure-caption-font-size:          $small-font-size !default;
 $figure-caption-color:              $gray-600 !default;
 
 
@@ -1108,7 +1112,7 @@ $close-text-shadow:                 0 1px 0 $white !default;
 
 // Code
 
-$code-font-size:                    87.5% !default;
+$code-font-size:                    $small-font-size !default;
 $code-color:                        $pink !default;
 
 $kbd-padding-y:                     .2rem !default;