BigCommerce Theme Performance Analysis

When it comes to ecommverce success, site performance is no longer optional. A slow-loading store can mean the difference between a sale and an abandoned cart. On top of that, Google now weighs speed and Core Web Vitals directly into search rankings, making performance both a conversion factor and an SEO factor.

For BigCommerce merchants, the theme you choose sets the foundation. A theme that looks sleek but loads slowly can quietly eat into your traffic and revenue. That’s why we set out to answer a straightforward question: which BigCommerce theme performance is best performance out of the box?

To find out, we ran a full analysis of every theme in the BigCommerce theme store. In this article, we’ll share those results, break down the top performers, and go a step further by looking at their heading structures to see which are most SEO-friendly. Along the way, we’ll also show how our own Epic Superstore theme stacks up.

Methodology

To ensure accuracy, we relied on the Google PageSpeed Insights API. Using the API allowed us to test all themes under the same conditions and at the same time, eliminating bias that might come from temporary traffic spikes or fluctuating server response times.

Here’s how the tests were run:

• Tool: Google PageSpeed Insights API.
• Scope: Every BigCommerce theme in the official theme store.
• Repetition: Each theme was tested five times per page type (homepage, category page, product page).
• Averaging: Results were averaged to smooth out temporary fluctuations.
• Metrics captured: Core Web Vitals, including Largest Contentful Paint (LCP), Interaction to Next Paint (INP, replacing FID), Cumulative Layout Shift (CLS), and the overall PageSpeed score.
• Devices tested: Both desktop and mobile versions were included.

By approaching it this way, we not only ensured fairness across all themes, but also gathered enough data to draw meaningful comparisons between them.

Performance Results

With the testing complete, we compiled the data into a single comparison table. This table shows the averaged Core Web Vitals for every BigCommerce theme, giving a clear snapshot of which ones load fast and which ones struggle.

Because numbers alone can be overwhelming, we’ve also highlighted the best performers with color coding — so you can quickly see where each theme stands:

• Green: Strong scores (top 5%) across Core Web Vitals (highly performant).
• Red: Noticeable performance issues (bottom 20%) that could impact SEO and conversions.

This is the first time (to our knowledge) that all BigCommerce themes have been benchmarked side-by-side in a controlled test environment. The goal isn’t to declare “winners” and “losers,” but to give merchants a realistic view of how themes perform before committing to one.

Top 3 Performing Themes

While the full table is helpful for broad comparisons, most merchants want to know: what are the best options right now? To make it easier, we’ve pulled out the top three performing themes based on our average scores.

For each, we’ll go beyond speed. A fast theme is great, but SEO depends heavily on a site’s heading structure — how H1, H2, and H3 tags are organized on key pages. A poor structure (like multiple H1s or skipped heading levels) can hold your site back even if your speed is excellent.

So for each of the top five themes, we’ll look at two things:

1. Performance results – how the theme scored in our Core Web Vitals testing.
2. Heading structure – a breakdown of the homepage, category page, and product page, highlighting how SEO-friendly the theme is out of the box.

This dual approach gives a fuller picture: speed and SEO.

The top 3 themes per our tests include Cornerstone, Epic Superstore, and Clariss.

The Cornerstone Theme

Cornerstone Light consistently lands near the top in our testing. It usually scores 80-90 on pagespeed insights making it one of the fastest, most stable themes available in the BigCommerce theme store.

This theme is also BigCommerce’s flagship theme, built in-house as the foundation for all other third-party themes. It has long been considered the best starting point for custom development, thanks to its simplicity and lean build. Without unnecessary fluff, it remains a top-three performer speed-wise.

Overall, the element hierarchy is logical, but there is still room for improvement in the HTML structure to make it more SEO-friendly.

Our Take:
Cornerstone Light is both fast and foundational. If you’re building from scratch or customizing heavily, it’s a reliable starting point. That said, merchants looking for out-of-the-box SEO optimizations may want to plan on refining the heading and HTML structure for best results.

Home Page

Category Page

Product Page

The Epic Superstore Theme

Epic Superstore is admittedly our own theme, but the results speak for themselves: it’s currently the fastest third-party theme in the BigCommerce theme store.

Built as a very minimal overlay on Cornerstone, Epic Superstore follows all of BigCommerce’s best practices while leaning into the way Cornerstone was originally designed. Rather than replacing major components, we made surgical improvements, touching as few files as possible while optimizing for speed and clean widget placements. The result is a lean theme that performs exceptionally well without sacrificing flexibility.

For merchants who want more control over content, we recommend pairing Epic Superstore with the Epic Page Builder Widgets app. This combination adds a full library of modular widgets, letting you customize layouts and messaging without bloating the theme.

The heading structure is intentionally succinct and streamlined, avoiding the excess baggage found in many other themes. This makes Epic Superstore not only fast, but also SEO-friendly right out of the box.

Our Take
Epic Superstore is designed to be the best of both worlds: the speed and stability of Cornerstone, with targeted enhancements that improve performance, SEO, and flexibility. For merchants who want a fast foundation that scales with their content, it’s hard to beat.

Home Page

Category Page

Product Page

The Clariss Theme

Clariss is a snappy theme that doesn’t get much attention, but in our testing it delivered quick load times and solid overall performance. On speed alone, it holds its own among the top performers.

That said, the theme comes with a ton of extra HTML heading elements baked into the markup. While these don’t slow the theme down, they can create unnecessary noise for search engines. We recommend cleaning up the heading structure before launch to avoid SEO confusion.

Our Take
Clariss is a good option if you want a less common theme that still performs well. Just be prepared to do some upfront housekeeping in the HTML structure to make it as SEO-friendly as its speed scores suggest.

Home Page

Category Page

Product Page

Key Takeaways

• Performance matters: Fast themes improve both conversion rates and SEO rankings.
• Structure matters too: Even the quickest theme can hold you back if the HTML heading structure is cluttered.
• Cornerstone Light is a reliable, lean foundation but needs some SEO refinement.
• Clariss delivers quick load times but requires cleanup before launch.
• Epic Superstore combines the best of both worlds — minimal, fast, and SEO-friendly right out of the box.

Conclusion

Choosing the right BigCommerce theme is about more than just design. Speed and SEO structure can have a direct impact on how well your store performs and how easily customers can find you.

We encourage you to test your own theme with the PageSpeed Insights API or the Pagespeed Insights web tool and also take a closer look at its heading structure before going live. If you’re looking for a theme that balances speed, flexibility, and SEO readiness, our Epic Superstore theme was built with exactly that in mind.

Check out Epic Superstore in the BigCommerce Theme Store.