It is possible to show the word “FREE” as the price instead of $0.00 in WooCommerce when the product is actually free.

Showing the word Free instead of $0.00 is more noticeable to users and less confusing especially when just want to add some free products or gifts for your customers to choose from.

All you need to do is add the following code snippet to your theme’s function.php file:

/**
* @snippet       Display FREE if Price Zero or Empty - WooCommerce Single Product
* @author        Vigilante Marketing
* @testedwith    WooCommerce 3.8
*/
  
add_filter( 'woocommerce_get_price_html', 'vm_price_free_zero_empty', 9999, 2 );
   
function vm_price_free_zero_empty( $price, $product ){
    if ( '' === $product->get_price() || 0 == $product->get_price() ) {
        $price = '<span class="woocommerce-Price-amount amount">FREE</span>';
    }  
    return $price;
}