How to identify each type
A block theme's folder contains a theme.json file at its root and a /templates directory with HTML files like index.html and single.html. A classic theme's folder instead contains PHP files: index.php, single.php, header.php, footer.php, and typically a functions.php with far more custom logic than a block theme needs.
You can also tell from wp-admin: block themes show a full-page "Editor" under Appearance for editing templates directly, while classic themes show a "Customize" panel limited to whatever settings the developer explicitly registered.
theme.json in practice
theme.json lets a block theme define a fixed color palette, font size scale, and spacing units once, and WordPress enforces those choices consistently in both the block editor and the front end. This removes a common inconsistency in classic themes where the editor preview and the live site could diverge if CSS was not kept perfectly in sync with editor styles.
It also controls layout constraints, like a default content width and a wider "wide" alignment width, which used to require manual CSS in classic themes and now live as a couple of numeric values in JSON.
Editing experience differences
In a block theme, changing your site's header means opening the Site Editor, selecting the header template part, and editing it with the same block interface used for post content — no PHP required. In a classic theme, the same change usually means editing header.php directly, or relying on a plugin/builder to inject a customizable header region.
This makes block themes noticeably friendlier for non-developers doing ongoing maintenance, while classic themes put more control (and more responsibility) in the hands of whoever can edit PHP.
Plugin and ecosystem compatibility
The overwhelming majority of WordPress plugins work fine with either theme type, since plugin functionality mostly runs independent of templates. The friction shows up specifically with plugins that hook into classic theme functions like wp_head(), wp_footer(), or the Customizer API, or with older page builders that were designed years before block themes existed.
If your site depends on a specific plugin, checking its changelog and support forum for explicit block-theme compatibility notes before switching is worth the five minutes it takes.
- Block theme pros: visual editing, consistent theme.json styling, no PHP required for layout tweaks
- Block theme cons: newer, still maturing for complex custom layouts
- Classic theme pros: mature, huge plugin/builder ecosystem, predictable
- Classic theme cons: structural changes need code or a separate builder plugin
Performance considerations
Block themes tend to load with less bundled CSS and JavaScript because styling is generated from theme.json rather than shipped as large stylesheet files, and there is no separate page-builder runtime to load. Classic themes paired with heavy page builders often carry more overhead, though a lean, well-coded classic theme can be just as fast as any block theme — theme quality matters more than category here.
Converting an existing design
If you already have a finished design — a live page, a Figma file, or a prototype — that needs to become a working WordPress theme, most conversion tools, including Themify, output a classic theme structure by default because it maps directly onto arbitrary HTML and CSS without requiring you to rebuild everything as blocks first. You can always adopt block-theme features later, or use a classic theme as a stable landing point while you decide whether Full Site Editing fits your workflow.
Frequently asked questions
- Can a classic theme be converted to a block theme?
- Not automatically. Converting requires rebuilding PHP templates as block-based HTML templates and defining a theme.json, which is a manual redesign process rather than a simple export.
- Are block themes required going forward?
- No, WordPress core continues to support classic themes, and there is no announced plan to remove that support, since millions of active sites and plugins still depend on it.
- Which one is easier for beginners?
- Block themes are generally easier for non-developers doing day-to-day edits, since the Site Editor is visual and requires no PHP knowledge, unlike editing classic theme template files.
- Do block themes support child themes?
- Yes, block themes support child themes with their own theme.json that can override or extend the parent's settings, similar in spirit to how classic child themes override parent styles.
- Is a hybrid theme a real category?
- Yes, some themes mix classic PHP templates with partial block-editor support, often to ease migration; these are informally called hybrid themes and are less common than pure classic or pure block themes.