Common Misconceptions about Google Lighthouse Scores

Relying on a singular score to determine your conversion rate—and ultimately your revenue—may be holding you back.

Google Lighthouse scores are designed to help you gauge your site’s web performance. In many ways, they can feel like an exam grade for your ecommerce site performance.

For starters, ecommerce brands compete to outperform one another by achieving the highest possible scores. And in much the same way that some people are just really good at exams, some ecommerce sites are optimized specifically to achieve high Lighthouse scores. But how effective is this optimization strategy in the long term?

In this article, we’ll dig into the complex world of Google Lighthouse scores. Ultimately, there are two key takeaways.

First, faster stores help create better shopper experiences, which lead to higher conversion rates. Second, Shopify’s stores are fast by default, meaning you don’t have to dedicate additional time and resources on making your store fast. With that in mind, let’s dive into the world of Google Lighthouse scores.

What is a Google Lighthouse score?

Google Lighthouse is the most commonly used tool for evaluating the performance of web pages. Its primary function is to assess your site’s loading and responsiveness performance.

To do this, Google looks at five crucial subjects: performance, accessibility, best practices, SEO, and progressive web apps. Lighthouse distills all this analysis into an easy-to-understand Google Lighthouse score.

The performance score is colored according to these ranges:

• 0 to 49 (red): Poor
• 50 to 89 (orange): Needs improvement
• 90 to 100 (green): Good

For years, the Lighthouse score has been used as a proxy for good user experience. The aim was to achieve the best score possible in that top band (90–100), because, according to Shopify data and research, increasing your site speed by even a half second can increase your conversion rate. (Since you asked, the average Shopify site speed is an impressive 1.2 seconds.)

See how your site speed stacks up with our Site Speed Audit.

How are Google Lighthouse scores calculated?

Google Lighthouse generates scores by analyzing the performance metrics gathered during simulated testing. These metrics provide insights into the speed at which a webpage loads and its ability to promptly respond to user interactions.

Lighthouse scores are calculated based on a minefield of acronyms. If you don’t work on web performance daily, here's a quick refresher:

• First Contentful Paint (FCP): When the browser renders the first bit of content, giving the feedback to the user that the page is loading.
• Largest Contentful Paint (LCP): This approximates when the main content of the page is visible to users.
• Speed index: Measures how quickly content is visually displayed during page load. Lighthouse captures a video of the page loading in the browser and calculates the visual progression between frames.
• Total Blocking Time (TBT): Measures the amount of time that a page is blocked from responding to user input, such as mouse clicks, screen taps, or keyboard presses.
• Cumulative Layout Shift (CLS): Quantify how often users experience unexpected layout shifts—a low CLS helps ensure that the page is visually stable.

Source: Google

Each audit generates a raw score, which is then weighted depending on the impact they have on user experience. Interestingly, Contentful Paint is only 10% of your overall Lighthouse score. However, we believe it's one of the most important site speed metrics (and so do many of our customers). Your Google Lighthouse score is the weighted average of all the scores. 

Speed is, of course, a particularly important aspect of performance for ecommerce businesses. Every lost millisecond represents lost revenue, with 57% of shoppers saying they have left a slow site to buy from a competitor.

But if your Google Lighthouse score is the only metric you use to measure your ecommerce site’s web performance, we have some bad news (their value is limited). Then some good news (Shopify has the right tools built in).

The limitations of Google Lighthouse scores

The fundamental problem with Google Lighthouse scores is this: thinking about performance as a single score is unhelpful. Google admits as much, stating: “Even though Lighthouse provides this single overall Performance score, you should think of your site performance as a distribution of scores, rather than a single number.”

Google Lighthouse scores do have their uses. When it comes to debugging and preliminary testing of optimizations, it can be a really useful reference tool. Problems arise because many companies treat a Lighthouse score as the end goal of their optimization efforts. It’s fallen prey to Goodhart’s law: “When a measure becomes a target, it ceases to be a good measure.”

In fact, a whole cottage industry has been built around artificially improving your Shopify speed score (which is based on your Google Lighthouse score) using methods that actually worsen user experience. So, if you’re seeking support you can trust, we always recommend using the Shopify Partner Directory. There you can find independent designers, developers and consultants chosen for their deep knowledge and successful track record.

Regardless of who supports your website optimization efforts, remember that improving your Lighthouse score doesn't necessarily translate to better site performance. Page speed and user experience (UX) simply can't be accurately represented by a single number.

Google Lighthouse vs. real user monitoring

It's also important to recognize that Lighthouse scores are derived from a controlled environment. Lighthouse only measures a snapshot in time in a simulated lab setting. This means fixing your Lighthouse score doesn’t necessarily equate to improving site performance. For real performance insights, you need to move beyond lab tests, to real user monitoring data.

Real user monitoring with tools like the Chrome User Experience Report (CrUX) offers a more nuanced understanding of how actual users interact with and perceive your website. This gives you the right foundation for improving UX and driving conversion rates.

Google Lighthouse score vs. the new Web Performance Dashboard

Our Web Performance Dashboard marks a significant improvement in website performance evaluation. Unlike the isolated perspective offered by Google Lighthouse scores, Shopify’s Web Performance Dashboard integrates Core Web Vitals and real user data.

This gives you a much more comprehensive performance assessment. With real user data at your fingertips, you can address the performance issues that directly impact user experience and ultimately influence conversion rates.

See how your site speed stacks up with our Site Speed Audit.

The cost of in-house web performance teams

Understandably, enterprise ecommerce businesses have been keen to explore taking web performance in-house to stay at the bleeding edge of innovation in ecommerce. The majority have discovered that doing so is not only expensive, but difficult to keep up with.

IT infrastructure is often one of the biggest expenses for a DTC retailer. And those costs have been rising steadily over the last few years with no signs of stopping. According to recent BLS data, cloud services are projected to make up 14.2% of total information technology (IT) spending worldwide by 2024, up from 9.1% of spending in 2020.

In response, many companies attempt to reduce their monthly costs by making surprisingly costly tradeoffs on their website. Many performance experts will start by reducing the size of product images across the entire site. While this may increase your site speed and reduce costs, it’s a big tradeoff.

Web performance: Shopify vs. the rest

Web performance is a critical factor in the success of ecommerce businesses. While Google Lighthouse scores may provide a baseline for comparison, it’s clear that businesses should focus more on Core Web Vitals. Let’s take a look at how Shopify stacks up on this front compared to other ecommerce platforms*:

BigCommerce

• On average, Shopify stores are 1.4x faster than BigCommerce stores
• 93% of Shopify stores are fast vs only 80% of BigCommerce stores
• Shopify’s server speed is 1.9x faster than BigCommerce’s

Salesforce Commerce Cloud

• On average, Shopify stores are 1.5x faster than Salesforce stores
• 93% of Shopify stores are fast vs only 65% of Salesforce stores
• Shopify’s server speed is 2.2x faster than Salesforce’s

Adobe (Magento) 

• On average, Shopify stores are 2x faster than Adobe stores
• 93% of Shopify stores are fast vs only 53% of Adobe stores
• Shopify’s server speed is 3.4x faster than Adobe’s

WooCommerce

• On average, Shopify stores are 2.4x faster than WooCommerce stores
• 93% of Shopify stores are fast vs only 34% of WooCommerce stores
• Shopify’s server speed is 3.9x faster than WooCommerce’s

*According to data from Google’s Core Web Vitals (CWV), collected for a representative sample of sites on Shopify and its competitors. Specifically, the first two data points for each competitor look at First Contentful Paint, while the third data point looks at Time to First Byte. To learn more, read the full report.

In the past year we have expanded our infrastructure, resulting in 35% faster performance. Correspondingly, 93% of brands on Shopify have a fast store, more than any other major commerce platform. Shopify invests more than $1 billion every year on R&D, so you don’t have to. In ourWinter 2024 Editions, we announced over 100 new foundational product updates designed to help enterprises elevate their commerce businesses. This summer, we announced over 150 new features and updates.

Each one feeds into our broader goal—helping ecommerce businesses perform better. That’s precisely what we did for Molekule. Their checkout page loading times ballooned to over a minute on their previous platform. Since migrating to Shopify, the company has seen a drastic jump in both site speed and conversion rates:

• 75% increase in device conversion rate
• 7% growth in net subscribers
• 10% increase in traffic

“Our transition to Shopify has supercharged our ecommerce performance and facilitated a complete turnaround in our subscription revenue growth.”

Rachel Beisel, Senior Vice President of Marketing, Molekule

A more holistic approach to website performance

In enterprise ecommerce, website optimization needs to be as holistic as possible. That means transcending metrics like Google Lighthouse scores. At Shopify, we champion an iterative approach that not only enhances website performance but fosters sustained growth in the maturing digital landscape. 

By embracing real user monitoring, making the most of tools like the Web Performance Dashboard, and using a continuous integration/continuous delivery (CI/CD) approach to optimization, you can cultivate a more user-centric mindset.

One final tip is to always ask commercially relevant performance questions, rather than trying to improve performance for its own sake. For example:

• Pageviews and sessions: Are more users browsing?
• Average pageviews per session: Are your users staying on your website longer?
• Number of add to carts per session: Are your users interacting with the cart more often?
• Checkout funnel: Are more users reaching the checkout?
• Number of transactions: Are more users buying?
• Average order value (AOV): Are your users buying more?

All these questions are good reminders that performance isn't just about enhancing the website—it's about improving the experience. When users have a smoother, more satisfying experience, they are more likely to stay longer and engage more deeply. And ultimately, this can lead to increased conversions and revenue.

See how your site speed stacks up with our Site Speed Audit.