WordPress default thumbnail sizes don’t fit your design? Create custom sizes.
Add to functions.php:
// Create custom thumbnail size
add_image_size('custom-thumb', 400, 300, true);
// Parameters: name, width, height, crop (true/false)
// Multiple sizes
add_image_size('hero-image', 1920, 600, true);
add_image_size('product-thumb', 300, 300, true);
add_image_size('blog-featured', 800, 400, true);
Use in Templates:
the_post_thumbnail('custom-thumb');
// Or get URL:
$url = get_the_post_thumbnail_url(get_the_ID(), 'custom-thumb');
Regenerate Existing Images: Install “Regenerate Thumbnails” plugin to create new sizes for old uploads.