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How do I add a custom image size and use it in a theme template?

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How do I add a custom image size and use it in a theme template?

Asked on Aug 29, 2025

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To add a custom image size in WordPress, you can use the `add_image_size()` function in your theme's `functions.php` file. Once the custom size is registered, you can display it in your theme templates using the `the_post_thumbnail()` function with the custom size name.

<!-- BEGIN COPY / PASTE -->
    // Add this to your theme's functions.php
    add_action('after_setup_theme', 'my_custom_image_sizes');
    function my_custom_image_sizes() {
        add_image_size('custom-size', 800, 600, true); // 800px wide by 600px tall, hard crop mode
    }

    // Use this in your theme template file
    if (has_post_thumbnail()) {
        the_post_thumbnail('custom-size');
    }
    <!-- END COPY / PASTE -->

Additional Comment:

Use `add_image_size()` to define custom dimensions and cropping behavior.
Ensure `after_setup_theme` is used to hook the image size registration, allowing it to load after the theme is set up.
Regenerate thumbnails using a plugin like "Regenerate Thumbnails" if you add new sizes after images are already uploaded.
In your template, check for a post thumbnail with `has_post_thumbnail()` before calling `the_post_thumbnail()` to avoid errors.

✅ Answered with WordPress best practices.

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How do I add a custom image size and use it in a theme template?

Asked on Aug 29, 2025

Answer

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