How to change product thumbnail size in storefront theme

I can’t take credit for this one, but I found the answer at themebynumbers.com

In my storefront-child folder I have added this to my functions.php file:

add_filter( 'woocommerce_get_image_size_thumbnail', function( $size ) {
  return array(
    'width'  => 150,
    'height' => 150,
    'crop'   => 1,
  );
});