Kadence Blocks vs Spectra vs GenerateBlocks: What Each One Costs Your Site

Kadence Blocks vs Spectra is one of the most common questions from people building with the block editor, and GenerateBlocks is the light alternative. We installed all three on the same site to see what they cost before you add a single block.

Block plugins add layout and design blocks to the WordPress editor. We tested the three most common free ones with the Kadence theme on a page that used only core blocks, to see what each one costs before you use a single block.

Kadence Blocks vs Spectra vs GenerateBlocks: our picks

1. GenerateBlocks — lightest block plugin

9.7/10 Free plan v2.5.0 · 200,000+ installs · 4.9★ on WordPress.org

GenerateBlocks gives you a small set of flexible building blocks instead of dozens of ready-made widgets. It added nothing to the front end, 1.6 MB of memory and no menus beyond its own two-item settings page.

2. Spectra (Legacy) — most blocks for the weight

9.5/10 Free plan v2.20.5 · 1 million+ installs · 4.7★ on WordPress.org

Spectra (now listed as “Spectra Legacy” on WordPress.org) added only about 1 KB of inline CSS and 4.4 MB of memory. It adds an onboarding menu item and an admin-bar entry.

3. Kadence Blocks — best with the Kadence theme

8.0/10 Free plan v3.8.0.1 · 600,000+ installs · 4.8★ on WordPress.org

Kadence Blocks has the richest free block set of the three (rows, tabs, accordions, forms, icons, advanced buttons) and it shares design settings with the Kadence theme. But on our test page — which used none of its blocks — it added 32 KB of inline CSS, and it had the highest memory cost (19.8 MB). No notices or nags.

Kadence Blocks vs Spectra: the real differences

• Block library: Kadence Blocks and Spectra both ship a large set of ready-made blocks (tabs, accordions, info boxes, forms). GenerateBlocks gives you a few flexible building blocks instead.
• Theme fit: Kadence Blocks shares colours and fonts with the Kadence theme; Spectra is made by the Astra team and fits Astra best. Both work with any block theme.
• Front-end weight: on our test page, which used none of their blocks, Kadence Blocks added 32 KB of inline CSS and Spectra about 1 KB.
• Server cost: Kadence Blocks added 19.8 MB of PHP memory, Spectra 4.4 MB and GenerateBlocks 1.6 MB.

How to keep any block plugin light

1. Turn off the blocks you never use in the plugin’s settings screen.
2. Avoid installing two block libraries at the same time.
3. Use core WordPress blocks for simple layouts; save the plugin blocks for tabs, accordions and complex rows.
4. Re-test your Core Web Vitals after adding a new block library.

Score breakdown: where each plugin gained and lost points

Our test score adds up five criteria. The table shows each plugin’s points per criterion (out of 10), followed by what we measured. A higher number is always better here.

Front-end weight (30%)

We loaded a normal page that does not use the plugin and counted the extra CSS and JavaScript files. Every 25 KB costs one point. GenerateBlocks added nothing to that page. Spectra (Legacy) added 1 KB of inline CSS. Kadence Blocks added 32 KB of inline CSS.

Server cost (20%)

Extra PHP memory per request ranged from 1.6 MB (GenerateBlocks) to 19.8 MB (Kadence Blocks). Memory matters on shared hosting, where every visitor request runs the plugin code. Database tables created: GenerateBlocks 0, Spectra (Legacy) 0 and Kadence Blocks 4. We deduct 0.35 points per MB of memory and 0.1 points per table.

Admin clutter (20%)

We counted what appeared in the dashboard right after activation. GenerateBlocks added nothing beyond its own menu. Spectra (Legacy) added an admin-bar menu. Kadence Blocks added nothing beyond its own menu.

WordPress.org trust (20%)

This is the WordPress.org rating, pulled toward 8/10 when a plugin has few reviews so that a handful of five-star ratings cannot win on its own. GenerateBlocks: 4.9 stars from 122 reviews, 200,000+ active installs. Spectra (Legacy): 4.7 stars from 1,872 reviews, 1 million+ active installs. Kadence Blocks: 4.8 stars from 332 reviews, 600,000+ active installs.

Maintenance (10%)

GenerateBlocks 2.5.0 was last updated 9 days before our test and is marked as tested up to WordPress 7.1.3. Spectra (Legacy) 2.20.5 was last updated 13 days before our test and is marked as tested up to WordPress 7.1.3. Kadence Blocks 3.8.0.1 was last updated 3 days before our test and is marked as tested up to WordPress 7.1.3. Plugins tested with the current WordPress version get full points; an update older than six months costs three points.

Which block plugin we would install today

If you want speed first, install GenerateBlocks. It added 1.6 MB of memory, no tables and no CSS on pages that do not use its blocks, and it scored 9.7 in our test.

If you want more ready-made blocks and you use the Kadence theme, Kadence Blocks is the natural pairing, but it was the heaviest here at 19.8 MB of memory and 32 KB of inline CSS. Spectra sits in between and has the biggest user base of the three.

Do not install all three. Each block plugin loads its own editor scripts, and mixing them makes pages harder to edit and slower to load.

How we tested

Every plugin was installed from WordPress.org on a clean WordPress 7.1.3 site (PHP 8.3, Kadence theme, default content) in WordPress Playground on 22 October 2026. We took a snapshot before and after activating each plugin, one plugin at a time, and compared them: CSS and JavaScript added to a logged-out page that doesn’t use the plugin, extra PHP memory to load WordPress, database tables, and every admin notice, dashboard widget and setup redirect. Directory facts (version, installs, rating) come from the WordPress.org API on the same day.

The WPGlory test score rates what a plugin costs your site, not how many features it has: front-end weight 30%, server cost 20%, admin clutter and upsells 20%, WordPress.org rating 20%, maintenance 10%. Features are covered in the text. Full method.

FAQ

Modasser Jasim

Meet Modasser, an industry specialist, website designer, and developer with professional experience. With over 5 years of expertise in crafting interactive websites and providing intelligent business solutions, Modasser has established a solid reputation for excellence in the industry.

I install every plugin on a clean test site and publish the numbers.

More postsHow we testwpglory.com