Constants defined during WordPress initialization. Many can be overridden in wp-config.php.

Version Constants

Defined in wp-includes/version.php:

Size Constants

Defined in wp_initial_constants():

define( 'KB_IN_BYTES', 1024 );
define( 'MB_IN_BYTES', 1024 * KB_IN_BYTES );         // 1,048,576
define( 'GB_IN_BYTES', 1024 * MB_IN_BYTES );         // 1,073,741,824
define( 'TB_IN_BYTES', 1024 * GB_IN_BYTES );         // 1,099,511,627,776
define( 'PB_IN_BYTES', 1024 * TB_IN_BYTES );
define( 'EB_IN_BYTES', 1024 * PB_IN_BYTES );
define( 'ZB_IN_BYTES', 1024 * EB_IN_BYTES );
define( 'YB_IN_BYTES', 1024 * ZB_IN_BYTES );

Since: 4.4.0 (PB through YB added in 6.0.0)

Time Constants

Defined in wp_initial_constants():

define( 'MINUTE_IN_SECONDS', 60 );
define( 'HOUR_IN_SECONDS', 60 * MINUTE_IN_SECONDS );     // 3,600
define( 'DAY_IN_SECONDS', 24 * HOUR_IN_SECONDS );        // 86,400
define( 'WEEK_IN_SECONDS', 7 * DAY_IN_SECONDS );         // 604,800
define( 'MONTH_IN_SECONDS', 30 * DAY_IN_SECONDS );       // 2,592,000
define( 'YEAR_IN_SECONDS', 365 * DAY_IN_SECONDS );       // 31,536,000

Note: These are approximations. Use DateTime class for precise calculations.

Since: 3.5.0 (MONTH_IN_SECONDS added in 4.4.0)

Memory Constants

Defined in wp_initial_constants():

Override in wp-config.php:

define( 'WP_MEMORY_LIMIT', '128M' );
define( 'WP_MAX_MEMORY_LIMIT', '512M' );

Debug Constants

Defined in wp_initial_constants():

Configuration Examples:

// Development setup
define( 'WP_DEBUG', true );
define( 'WP_DEBUG_DISPLAY', true );
define( 'WP_DEBUG_LOG', true );

// Production setup with logging
define( 'WP_DEBUG', true );
define( 'WP_DEBUG_DISPLAY', false );
define( 'WP_DEBUG_LOG', '/path/to/debug.log' );

// Use global display_errors setting
define( 'WP_DEBUG_DISPLAY', null );

Development Constants

Configuration:

define( 'WP_DEVELOPMENT_MODE', 'theme' );
define( 'SCRIPT_DEBUG', true );

Cache Constants

Path Constants

Core Paths

Plugin Paths

Defined in wp_plugin_directory_constants():

Language Paths

Defined in wp_set_lang_dir():

Template Paths

Defined in wp_templating_constants():

Use instead: get_template_directory() and get_stylesheet_directory()

Cookie Constants

Defined in wp_cookie_constants():

SSL Constants

Defined in wp_ssl_constants():

Functionality Constants

Defined in wp_functionality_constants():

Disable revisions:

define( 'WP_POST_REVISIONS', false );

Limit revisions:

define( 'WP_POST_REVISIONS', 5 );

Theme Constants

Defined in wp_templating_constants():

Media Constants

Environment Constants

Values: 'local', 'development', 'staging', 'production'

Request Type Constants

Set during request processing:

Special Load Constants

Security Constants

Multisite Constants

Feature Constants

Timestamp Constants

Defining Constants

Constants should be defined in wp-config.php before require_once ABSPATH . 'wp-settings.php':

// Example wp-config.php

// Debug settings
define( 'WP_DEBUG', true );
define( 'WP_DEBUG_LOG', true );
define( 'WP_DEBUG_DISPLAY', false );
define( 'SCRIPT_DEBUG', true );

// Memory limits
define( 'WP_MEMORY_LIMIT', '256M' );
define( 'WP_MAX_MEMORY_LIMIT', '512M' );

// Custom content directory
define( 'WP_CONTENT_DIR', '/var/www/content' );
define( 'WP_CONTENT_URL', 'https://example.com/content' );

// Custom plugin directory
define( 'WP_PLUGIN_DIR', '/var/www/content/plugins' );
define( 'WP_PLUGIN_URL', 'https://example.com/content/plugins' );

// Revisions
define( 'WP_POST_REVISIONS', 10 );
define( 'AUTOSAVE_INTERVAL', 120 );

// Security
define( 'DISALLOW_FILE_EDIT', true );
define( 'FORCE_SSL_ADMIN', true );

// Cron
define( 'DISABLE_WP_CRON', true );  // If using system cron
define( 'ALTERNATE_WP_CRON', true ); // Alternative cron method

// Must be last
require_once ABSPATH . 'wp-settings.php';

Checking Constants

// Check if defined
if ( defined( 'WP_DEBUG' ) && WP_DEBUG ) {
    // Debug mode is on
}

// Check specific value
if ( defined( 'WP_ENVIRONMENT_TYPE' ) ) {
    $env = WP_ENVIRONMENT_TYPE;
} else {
    $env = 'production';
}

// Use helper functions when available
if ( function_exists( 'wp_get_environment_type' ) ) {
    $env = wp_get_environment_type();
}