1. Find User ID in WordPress Admin Area

This is a very simple method, but it also have some disadvantages. First – you should be logged in, second – you can not obtain the id of your own user.

So:

  1. Log into your WordPress admin
  2. Go to Users > All users
  3. Choose the user and go to his profile
  4. Look at the URL of the page:

2. Get Current User ID (and username, email etc)

The best way to get a currently logged in user ID is using get_current_user_id() function.

$current_user_id = get_current_user_id();

Absolutely the same way is with wp_get_current_user():

$current_user = wp_get_current_user();
$current_user_id = $current_user->ID;

The usage of get_current_user_id() seems simpler for me but you can use any way you want, because in the code they are the same. But wp_get_current_user() allows you at the same time to get current user email $current_user->user_email, first name $current_user->first_name, last name $current_user->last_name, username $current_user->user_login and display name $current_user->display_name.

But did you hear about get_currentuserinfo()? Should you use it? The answer is – no, this function is deprecated. Use wp_get_current_user() instead.

3. How to Get User ID by Email?

Simple enough. Just use get_user_by() function.

$the_user = get_user_by('email', '[email protected]');
$the_user_id = $the_user->ID;

Bonus: Get User Email by ID

First of all you can get user email with the same get_user_by() function.

$the_user = get_user_by( 'id', 54 ); // 54 is a user ID
echo $the_user->user_email;

The next method is just get_userdata() function, which is equal to get_user_by( 'id', ... )

$the_user = get_userdata( 54 );
echo $the_user->user_email;

4. Get User ID by Username (login name)

In the following example the second parameter “tom” is the username

$the_user = get_user_by('login', 'tom');
$the_user_id = $the_user->ID;

Is there a way to get username from user ID? Yes, just use get_userdata() or get_user_by( 'id', ... ). Just like the example with emails.

5. Get User ID by First Name or by Last Name

Print the ids of all users with the first name is “Misha”:

global $wpdb;
$users = $wpdb->get_results( "SELECT user_id FROM $wpdb->usermeta WHERE meta_key = 'first_name' AND meta_value = 'Misha'" );
if( $users ) {
	foreach ( $users as $user ) {
		echo '<p>' . $user->user_id . '</p>';
	}
} else {
	echo 'There are no users with the specified first name.';
}

Print the ids of all users with the last name is “Rudrastyh”:

global $wpdb;
$users = $wpdb->get_results( "SELECT user_id FROM $wpdb->usermeta WHERE meta_key = 'first_name' AND meta_value = 'Rudrastyh'" );
if( $users ) {
	foreach ( $users as $user ) {
		echo '<p>' . $user->user_id . '</p>';
	}
} else {
	echo 'There are no users with the specified last name.';
}

The code above will work if you would like to find user ID by any user meta value. Just replace meta_key and meta_value with the ones you need.

And of course you can get user first and last names and any meta with the help of get_user_meta( $id, $meta_key, true) function.

6. How to Get Author ID by Post ID?

In this case you can get the user ID from WP_Post object. It’s simple.

$my_post = get_post( $id ); // $id - Post ID
echo $my_post->post_author; // print post author ID

7. How to Get a Customer ID from an Order in WooCommerce?

There are two different ways to do it, the first one is just to get customer ID from order meta this way:

$customer_id = get_post_meta( 541, '_customer_user', true); // 541 is your order ID

The second one is with the help of WC_Order object. By the way this method will work only for WC 3.0+.

$order = wc_get_order( 541 ); // 541 is your order ID
$customer_id = $order->get_customer_id(); // or $order->get_user_id() – the same

8. Add the User ID column to the WordPress Users Table

Very useful way of getting user ids through WordPress admin. Here is the result:

How to create the same column on you own WordPress website? All you need to do is to copy the following code to you current theme functions.php file:

/*
 * Adding the column
 */
function rd_user_id_column( $columns ) {
	$columns['user_id'] = 'ID';
	return $columns;
}
add_filter('manage_users_columns', 'rd_user_id_column');
 
/*
 * Column content
 */
function rd_user_id_column_content($value, $column_name, $user_id) {
	if ( 'user_id' == $column_name )
		return $user_id;
	return $value;
}
add_action('manage_users_custom_column',  'rd_user_id_column_content', 10, 3);
 
/*
 * Column style (you can skip this if you want)
 */
function rd_user_id_column_style(){
	echo '<style>.column-user_id{width: 5%}</style>';
}
add_action('admin_head-users.php',  'rd_user_id_column_style');
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