Change size of startIcon / endIcon Material-UI

Question

I'm creating a theme in Material-UI and have to use our own set of icons (SVG). However, the icons gets too small when inserted in a button with startIcon / endIcon. Is there any way to increase the size of the icon and not the font. Preferably from the theme settings.

Here is an example of the button:
https://codesandbox.io/s/inspiring-spence-gsov0?file=/src/App.js

import React from "react";
import "./styles.css";
import Button from "@material-ui/core/Button";
import { SvgIcon } from "@material-ui/core";

function CloudIcon(props) {
  return (
    <SvgIcon {...props}>
      <svg viewBox="0 0 94 94" {...props}>
        <title>{"B Circle"}</title>
        <circle cx={47} cy={47} r={47} fill="#1700ff" />
        <title>{"\uF0C2"}</title>
        <path
          d="M61.9 61.6h-29c-6.3 0-11.3-5.1-11.3-11.3 0-5 3.2-9.3 7.9-10.8.2-7.2 6.2-13.1 13.5-13.1 4.4 0 8.4 2.1 10.9 5.6 1.2-.6 2.5-.9 3.9-.9 5.1 0 9.3 4.2 9.3 9.3 0 .5 0 1-.1 1.5 3.3 1.9 5.4 5.4 5.4 9.2 0 5.8-4.7 10.5-10.5 10.5zM43 28.4c-6.3 0-11.5 5.2-11.5 11.5V41l-.8.2c-4.2 1-7.2 4.7-7.2 9.1 0 5.2 4.2 9.3 9.3 9.3h28.9c4.7 0 8.5-3.8 8.5-8.5 0-3.3-1.9-6.3-4.9-7.7l-.6-.4.2-.8c.1-.6.2-1.2.2-1.8 0-4-3.3-7.3-7.3-7.3-1.3 0-2.6.3-3.7 1l-.8.5-.5-.8c-2.2-3.4-5.8-5.4-9.8-5.4z"
          fill="#fff"
        />
      </svg>
    </SvgIcon>
  );
}

export default function App() {
  return (
    <div className="App">
      <Button startIcon={<CloudIcon />} variant="outlined">
        Test
      </Button>
    </div>
  );
}

Answer 1

The default styles for the icon size can be found here (and shown below): https://github.com/mui-org/material-ui/blob/v4.11.0/packages/material-ui/src/Button/Button.js#L249. Which of the three is used depends on the size prop for the Button. medium is the default.

  /* Styles applied to the icon element if supplied and `size="small"`. */
  iconSizeSmall: {
    '& > *:first-child': {
      fontSize: 18,
    },
  },
  /* Styles applied to the icon element if supplied and `size="medium"`. */
  iconSizeMedium: {
    '& > *:first-child': {
      fontSize: 20,
    },
  },
  /* Styles applied to the icon element if supplied and `size="large"`. */
  iconSizeLarge: {
    '& > *:first-child': {
      fontSize: 22,
    },
  },

Below is an example of how to override this in the theme.

const theme = createMuiTheme({
  overrides: {
    MuiButton: {
      iconSizeMedium: {
        "& > *:first-child": {
          fontSize: 22
        }
      }
    }
  }
});

Answer 2

I had the same question and here is a possible solution if you don't want to make changes to your Theme. You can overwrite the nested iconSizeMedium CSS style at component level directly. Here is an example where a Button is wrapped with Typography letting it control the font-size through inherits:

import Button from '@material-ui/core/Button';
import PhoneEnabledIcon from '@material-ui/icons/PhoneEnabled';
import { makeStyles } from '@material-ui/styles';
import Typography from '@material-ui/core/Typography';

const useStyles = makeStyles((theme) => ({
    buttonRoot: {
        fontSize: 'inherit', /* inherit from Typography */
    },
    myIconSizeMedium: {
        "& > *:first-child": {
            fontSize: 'inherit'
        }
    }
}));

export default function MyButton( {children} ) {

    const classes = useStyles();

    return (
        <Typography color='textSecondary' variant="h6" >
            <Button
                startIcon={<PhoneEnabledIcon />}
                className={classes.buttonRoot}
                classes={{ iconSizeMedium: classes.myIconSizeMedium }}
            >
                {children}
            </Button>
        </Typography>
    )
}