The 10 Must-Track Web Performance Metrics

Web performance metrics track the efficiency (or lack thereof) of any individual aspect of your website’s performance. The first step in improving your website is measuring it. Web analytics such as click-through rates, bounce rates, website business transactions and sales, response times, web server usage, social media interaction, and many other key performance indicators will help ensure your site is optimal. Once you have started collecting some of these must-track web performance metrics for your website, inefficiencies will become clearer.

Top 10 Web Perf Metrics to Track

The amount of web performance data that can be collected is vast and somewhat overwhelming. Therefore, we have narrowed it down to the 10 most essential metrics to track web performance. Some of these are completely dependent on your technology, and others on your user’s behavior. Some may be harder to optimize than others, but with a little elbow grease you should be able to move the needle and improve each of them.

While going through this list, it’s important to keep in mind the overall goals of your website. While lots of these KPIs are speed metrics, content performance metrics, and behavioral metrics, don’t lose sight of your main purpose (perhaps revenue).

1. Time to First Byte

This is the time which elapses between a visitor’s mouse button clicking “go” and your website’s giving a response back to the browser. When the title takes too long to appear, it gives visitors an uneasy feeling as to the legitimacy of the website. The time to first byte (aka TTFB) is stipulated by the delivery speed from the website’s original server of origin to the viewer’s ISP.

2. Time to Start Render

The interval of time between a visitor’s request and the site content being displayed is the time to start render. The sooner a viewer is given content, the more readily they will become engaged. This is the biggest factor in how the user perceives how fast the site is, regardless of how fast it really is.

One of the most common forms of this measurement is the Speed Index, which measures how long it takes for most of the content ‘above the fold’ to render.

3. Time to Interactive

The time it takes between a viewer requesting site access to the ability for that viewer to interact with the requested website is the time to interact. For example, a user may be able to see the website, but not click on a button or hover over a menu because the browser is still busy loading other parts of it. While this is closely related to Time to Render, it is usually later and largely dependent on javascript. The larger the time to interact, the more likely it is for a visitor to abandon their request.

time to interactive

In the image above, you can see it takes 1.25 seconds before the page is interactive, but then it become ‘uninteractive’ between 2 and 3 seconds while the browser gets stuck loading additional content. Because the browser can become stalled even after it has been interactive, the true time to interactive is after there’s no more blips in interactivity.

4. DNS Lookup Time

This is a measurement of the time it takes for your domain name to be translated into an IP address, aka the DNS resolve process. Most hosts provide their own DNS servers, which is nice – but not always optimal. If you’re seeing DNS lookups above 100ms, consider a third party DNS service, such as DNSMadeEasy or CloudFlare.

5. Resource Download Time

Every single file that you reference in your website’s html has to be downloaded. Every font, css, javascript file, and image takes time to download. Looking at your page load ‘waterfall’ will show you all the resources and how long it takes to download each.


Using a CDN (or Content Delivery Network) can help lower these load times. A CDN copies your site’s static content to servers spread out all over the globe. Instead of everyone trying to access your content at the same time from your origin server, your website’s content is loaded from the server nearest to the user’s request. A cache server is another effective tool for reducing your website’s resource download times.

6. Website Weight in Bytes

Your website’s overall weight is measured in bytes. This is an important content performance metric, as it almost always negatively correlated with speed. Ie, the more your website weighs, the slower it takes to load.

You can lessen the load, by reducing image sizes, getting rid of unnecessary widgets, and implementing a minification or concatenation plugins.

7. Third-Party Resources

Most of the content on your website will be hosted by your servers. But it is common to utilize third-party content so you don’t have to create everything from scratch. Examples include website tracking analytics, remarketing pixels, social widgets, and ads/advertisements.

Not only can these significantly affect your website’s speed since they’re typically slow, it’s also scary to rely on this third-party content since they can change at any time without informing you. For example, that ‘Twitter Share’ widget can be upgraded to start including suggested tweets all without you knowing. This is one of the primary reasons for website speed monitoring.

8. Bounce Rate

Your website’s bounce rate is a behavioral metric, which refers to how often a user has left your website prior to interacting with the site’s content. If your bounce rate is high, you know that either your website is taking too long to load, or the user is not interested in your content (perhaps they are being misled). When your bounce rate is high, it also will negatively affect your website’s SEO.

9. Time on Site

Related to Bounce Rate is Time on Site – the average measure of how long a user stays on your domain looking at your site. If they click and go to another page on your website that’s included, but as soon as they go to a different domain the timer is stopped.

Note that while there’s usually not a literal clock counting the user’s behavior, this is measured as a sampled average across all users page load activity.

10. Conversion Rate

Your site’s conversion rate is a metric of how many of your site’s visitors engage in the action that you would like. This action could be a subscription list, a product sale, or a social media share, etc. When a website has a low conversion rate, this could indicate an inconsistency in the marketing of your website. Perhaps the wrong demographic is being targeted. At the end of the day, the goal of every website is to have a high conversion rate because it means that your website is operating effectively on all fronts.

How to measure these top performance metrics?

We have covered a lot of metrics here, and I hope you consider each as some of your key performance indicators that you use to track the performance of your website.

The good news is that all of these metrics can be measured reliably and consistently through the use of a website analytics platform (such as Google Analytics) and a speed monitoring service (such as MachMetrics). Both can be started for free and will give you the data you need to ensure your website is optimal.

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