Why TTFB Is Not the Best Indicator of Site Speed

By Paul Bernier

June 20, 2022


We all do our best to eliminate latency on our digital channels. It’s been shown time and time again that slow sites correlate to lower conversion rates and less engagement.[source] Reducing site speed is a good use of IT resources. However, most of us measure speed in a way that does not reflect the full picture: Time to First Byte (TTFB). Some optimization solutions insist on their latency-free model, but it’s worth considering what the real benefit there may be.

No Business Value, No Site Value

The digital channels you manage must ultimately enable brand engagement, conversions, or bring in revenue, and TTFB is only one piece of the puzzle when it comes to understanding how speed impacts those broader business metrics. While it gives you valuable insight into site function and is a healthy measure of network performance, it offers very little insight into the overall customer experience on the site.

TTFB is not a user-centric measurement, it’s a networking measurement.

Why is that? Because site speed and performance are much more than TTFB. Strictly speaking, TTFB is a measure of how fast a web server is able to respond to a request, and how long it takes for that request to traverse various layers of networking to reach a user’s browser. It is a measure of speed for delivery of content, but it is not a measurement for how long end-users are effectively waiting before they can start interacting with your website. TTFB completely ignores everything that happens after that network layer: loading, downloading of resources, rendering, etc. In other words, TTFB is not a user-centric measurement, it’s a networking measurement.

Page Load Time and Core Web Vitals

Page load time has long been the go-to metric for assessing how long a website takes to load from a user perspective. In simple terms, page load time is the time it takes for a page to load, measured from navigation start to the start of the load event. By definition, it includes TTFB, as well as the time the browser takes to render the experience.

Since then, Google has been pushing for broader adoption of the Core Web Vitals, an initiative to provide more relevant and user-centric measurements. It includes metrics such as Largest Contentful Paint (LCP) to more accurately represent how end-users perceive load time.

In both cases, TTFB is just a small subcomponent of the entire user experience:

TTFB Blog Image 1


It’s always a best practice to optimize TTFB, but don’t lose the big picture! Think about it this way:

  • A good TTFB is in the milliseconds range.
  • A good LCP is below 2.5 seconds.

Interested in checking your site performance? Check out this free tool: https://www.webpagetest.org/.

Reverse Proxy to the Rescue

While A/B testing variations by way of javascript tags or other development changes don’t typically impact TTFB, they do impact page load time and the user experience in much more significant ways. This means that while IT metrics may remain steady, business metrics can drop.

SiteSpect solves this practical problem. With a reverse proxy, TTFB increases slightly but has a negligible impact on overall page load time, LCP, and other web core vitals. Simply replacing your tag-based tool with SiteSpect might be one of the most impactful ways to improve user-centric performance metrics and page load time.

The reverse proxy speeds up the process overall, eliminating flicker and helping you score the metrics you need to keep the business goals in line.

TTFB Blog Image 2


If your end goal is to eliminate latency and improve the digital experience, you need to understand that TTFB is just one aspect when it comes to the big picture of understanding how site speed impacts business metrics. A reverse-proxy optimization solution, like SiteSpect, can improve your user-centric performance metrics and page load time.

Do you want to see SiteSpect in action? Schedule a personalized demo today!


Paul Bernier

Paul Bernier

Paul Bernier is Vice President of Product Management at SiteSpect. He has a background in website optimization, recommendations, and development, as well as web analytics. He is based in Boston.

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