diff --git a/docs/pages/api-docs/icon.md b/docs/pages/api-docs/icon.md
index 0a595c2b4c0969..30d7f836af3f6a 100644
--- a/docs/pages/api-docs/icon.md
+++ b/docs/pages/api-docs/icon.md
@@ -32,7 +32,7 @@ The `MuiIcon` name can be used for providing [default props](/customization/glob
 | <span class="prop-name">classes</span> | <span class="prop-type">object</span> |  | Override or extend the styles applied to the component. See [CSS API](#css) below for more details. |
 | <span class="prop-name">color</span> | <span class="prop-type">'inherit'<br>&#124;&nbsp;'primary'<br>&#124;&nbsp;'secondary'<br>&#124;&nbsp;'action'<br>&#124;&nbsp;'error'<br>&#124;&nbsp;'disabled'</span> | <span class="prop-default">'inherit'</span> | The color of the component. It supports those theme colors that make sense for this component. |
 | <span class="prop-name">component</span> | <span class="prop-type">elementType</span> | <span class="prop-default">'span'</span> | The component used for the root node. Either a string to use a HTML element or a component. |
-| <span class="prop-name">fontSize</span> | <span class="prop-type">'inherit'<br>&#124;&nbsp;'default'<br>&#124;&nbsp;'small'<br>&#124;&nbsp;'large'</span> | <span class="prop-default">'default'</span> | The fontSize applied to the icon. Defaults to 24px, but can be configure to inherit font size. |
+| <span class="prop-name">fontSize</span> | <span class="prop-type">'inherit'<br>&#124;&nbsp;'large'<br>&#124;&nbsp;'medium'<br>&#124;&nbsp;'small'</span> | <span class="prop-default">'medium'</span> | The fontSize applied to the icon. Defaults to 24px, but can be configure to inherit font size. |
 
 The `ref` is forwarded to the root element.
 
diff --git a/docs/pages/api-docs/svg-icon.md b/docs/pages/api-docs/svg-icon.md
index fe77312427e7d1..6536456496d9cf 100644
--- a/docs/pages/api-docs/svg-icon.md
+++ b/docs/pages/api-docs/svg-icon.md
@@ -32,7 +32,7 @@ The `MuiSvgIcon` name can be used for providing [default props](/customization/g
 | <span class="prop-name">classes</span> | <span class="prop-type">object</span> |  | Override or extend the styles applied to the component. See [CSS API](#css) below for more details. |
 | <span class="prop-name">color</span> | <span class="prop-type">'action'<br>&#124;&nbsp;'disabled'<br>&#124;&nbsp;'error'<br>&#124;&nbsp;'inherit'<br>&#124;&nbsp;'primary'<br>&#124;&nbsp;'secondary'</span> | <span class="prop-default">'inherit'</span> | The color of the component. It supports those theme colors that make sense for this component. You can use the `htmlColor` prop to apply a color attribute to the SVG element. |
 | <span class="prop-name">component</span> | <span class="prop-type">elementType</span> | <span class="prop-default">'svg'</span> | The component used for the root node. Either a string to use a HTML element or a component. |
-| <span class="prop-name">fontSize</span> | <span class="prop-type">'default'<br>&#124;&nbsp;'inherit'<br>&#124;&nbsp;'large'<br>&#124;&nbsp;'small'</span> | <span class="prop-default">'default'</span> | The fontSize applied to the icon. Defaults to 24px, but can be configure to inherit font size. |
+| <span class="prop-name">fontSize</span> | <span class="prop-type">'inherit'<br>&#124;&nbsp;'large'<br>&#124;&nbsp;'medium'<br>&#124;&nbsp;'small'</span> | <span class="prop-default">'medium'</span> | The fontSize applied to the icon. Defaults to 24px, but can be configure to inherit font size. |
 | <span class="prop-name">htmlColor</span> | <span class="prop-type">string</span> |  | Applies a color attribute to the SVG element. |
 | <span class="prop-name">shapeRendering</span> | <span class="prop-type">string</span> |  | The shape-rendering attribute. The behavior of the different options is described on the [MDN Web Docs](https://developer.mozilla.org/en-US/docs/Web/SVG/Attribute/shape-rendering). If you are having issues with blurry icons you should investigate this property. |
 | <span class="prop-name">titleAccess</span> | <span class="prop-type">string</span> |  | Provides a human-readable title for the element that contains it. https://www.w3.org/TR/SVG-access/#Equivalent |
diff --git a/packages/material-ui/src/Icon/Icon.d.ts b/packages/material-ui/src/Icon/Icon.d.ts
index b2d176b41014b2..a0c4c9443141ff 100644
--- a/packages/material-ui/src/Icon/Icon.d.ts
+++ b/packages/material-ui/src/Icon/Icon.d.ts
@@ -5,7 +5,7 @@ import { OverridableComponent, OverrideProps } from '../OverridableComponent';
 export interface IconTypeMap<P = {}, D extends React.ElementType = 'span'> {
   props: P & {
     color?: PropTypes.Color | 'action' | 'disabled' | 'error';
-    fontSize?: 'inherit' | 'default' | 'small' | 'large';
+    fontSize?: 'inherit' | 'large' | 'medium' | 'small';
   };
   defaultComponent: D;
   classKey: IconClassKey;
diff --git a/packages/material-ui/src/Icon/Icon.js b/packages/material-ui/src/Icon/Icon.js
index c2a91c420d7c35..c2fef53a6ceb00 100644
--- a/packages/material-ui/src/Icon/Icon.js
+++ b/packages/material-ui/src/Icon/Icon.js
@@ -1,8 +1,9 @@
 import * as React from 'react';
 import PropTypes from 'prop-types';
 import clsx from 'clsx';
-import withStyles from '../styles/withStyles';
+import { chainPropTypes } from '@material-ui/utils';
 import capitalize from '../utils/capitalize';
+import withStyles from '../styles/withStyles';
 
 export const styles = (theme) => ({
   /* Styles applied to the root element. */
@@ -56,7 +57,7 @@ const Icon = React.forwardRef(function Icon(props, ref) {
     className,
     color = 'inherit',
     component: Component = 'span',
-    fontSize = 'default',
+    fontSize = 'medium',
     ...other
   } = props;
 
@@ -67,7 +68,7 @@ const Icon = React.forwardRef(function Icon(props, ref) {
         classes.root,
         {
           [classes[`color${capitalize(color)}`]]: color !== 'inherit',
-          [classes[`fontSize${capitalize(fontSize)}`]]: fontSize !== 'default',
+          [classes[`fontSize${capitalize(fontSize)}`]]: fontSize !== 'medium',
         },
         className,
       )}
@@ -104,7 +105,17 @@ Icon.propTypes = {
   /**
    * The fontSize applied to the icon. Defaults to 24px, but can be configure to inherit font size.
    */
-  fontSize: PropTypes.oneOf(['inherit', 'default', 'small', 'large']),
+  fontSize: chainPropTypes(PropTypes.oneOf(['inherit', 'large', 'medium', 'small']), (props) => {
+    const { fontSize } = props;
+
+    if (fontSize === 'default') {
+      throw new Error(
+        'Material-UI: `fontSize="default"` is deprecated. Use `fontSize="medium"` instead.',
+      );
+    }
+
+    return null;
+  }),
 };
 
 Icon.muiName = 'Icon';
diff --git a/packages/material-ui/src/Radio/Radio.js b/packages/material-ui/src/Radio/Radio.js
index d4c855d7f8b080..c403b8976903d8 100644
--- a/packages/material-ui/src/Radio/Radio.js
+++ b/packages/material-ui/src/Radio/Radio.js
@@ -85,9 +85,9 @@ const Radio = React.forwardRef(function Radio(props, ref) {
     <SwitchBase
       color={color}
       type="radio"
-      icon={React.cloneElement(defaultIcon, { fontSize: size === 'small' ? 'small' : 'default' })}
+      icon={React.cloneElement(defaultIcon, { fontSize: size === 'small' ? 'small' : 'medium' })}
       checkedIcon={React.cloneElement(defaultCheckedIcon, {
-        fontSize: size === 'small' ? 'small' : 'default',
+        fontSize: size === 'small' ? 'small' : 'medium',
       })}
       classes={{
         root: clsx(classes.root, classes[`color${capitalize(color)}`]),
diff --git a/packages/material-ui/src/Radio/RadioButtonIcon.js b/packages/material-ui/src/Radio/RadioButtonIcon.js
index 27ea827ef13908..737d4bf45f05cf 100644
--- a/packages/material-ui/src/Radio/RadioButtonIcon.js
+++ b/packages/material-ui/src/Radio/RadioButtonIcon.js
@@ -57,7 +57,7 @@ RadioButtonIcon.propTypes = {
    * The size of the radio.
    * `small` is equivalent to the dense radio styling.
    */
-  fontSize: PropTypes.oneOf(['small', 'default']),
+  fontSize: PropTypes.oneOf(['small', 'medium']),
 };
 
 export default withStyles(styles, { name: 'PrivateRadioButtonIcon' })(RadioButtonIcon);
diff --git a/packages/material-ui/src/SvgIcon/SvgIcon.d.ts b/packages/material-ui/src/SvgIcon/SvgIcon.d.ts
index 2290bbd4a7bb44..77d11f0eede2b4 100644
--- a/packages/material-ui/src/SvgIcon/SvgIcon.d.ts
+++ b/packages/material-ui/src/SvgIcon/SvgIcon.d.ts
@@ -15,7 +15,7 @@ export interface SvgIconTypeMap<P = {}, D extends React.ElementType = 'svg'> {
     /**
      * The fontSize applied to the icon. Defaults to 24px, but can be configure to inherit font size.
      */
-    fontSize?: 'inherit' | 'default' | 'small' | 'large';
+    fontSize?: 'inherit' | 'large' | 'medium' | 'small';
     /**
      * Applies a color attribute to the SVG element.
      */
diff --git a/packages/material-ui/src/SvgIcon/SvgIcon.js b/packages/material-ui/src/SvgIcon/SvgIcon.js
index d3e264963cc53a..e9ab0e228f550c 100644
--- a/packages/material-ui/src/SvgIcon/SvgIcon.js
+++ b/packages/material-ui/src/SvgIcon/SvgIcon.js
@@ -1,8 +1,9 @@
 import * as React from 'react';
 import PropTypes from 'prop-types';
 import clsx from 'clsx';
-import withStyles from '../styles/withStyles';
+import { chainPropTypes } from '@material-ui/utils';
 import capitalize from '../utils/capitalize';
+import withStyles from '../styles/withStyles';
 
 export const styles = (theme) => ({
   /* Styles applied to the root element. */
@@ -59,7 +60,7 @@ const SvgIcon = React.forwardRef(function SvgIcon(props, ref) {
     className,
     color = 'inherit',
     component: Component = 'svg',
-    fontSize = 'default',
+    fontSize = 'medium',
     htmlColor,
     titleAccess,
     viewBox = '0 0 24 24',
@@ -72,7 +73,7 @@ const SvgIcon = React.forwardRef(function SvgIcon(props, ref) {
         classes.root,
         {
           [classes[`color${capitalize(color)}`]]: color !== 'inherit',
-          [classes[`fontSize${capitalize(fontSize)}`]]: fontSize !== 'default',
+          [classes[`fontSize${capitalize(fontSize)}`]]: fontSize !== 'medium',
         },
         className,
       )}
@@ -121,7 +122,18 @@ SvgIcon.propTypes = {
   /**
    * The fontSize applied to the icon. Defaults to 24px, but can be configure to inherit font size.
    */
-  fontSize: PropTypes.oneOf(['default', 'inherit', 'large', 'small']),
+  fontSize: chainPropTypes(PropTypes.oneOf(['inherit', 'large', 'medium', 'small']), (props) => {
+    const { fontSize } = props;
+
+    if (variant === 'default') {
+      throw new Error(
+        'Material-UI: `variant="default"` is deprecated. Use `variant="medium"` instead.',
+      );
+    }
+
+    return null;
+  }),
+
   /**
    * Applies a color attribute to the SVG element.
    */