TTFB and TTI: 2 KPIs More Important Than Page Load Speed



Do you think page load speed is your target performance KPI? Think again. I want to introduce you to 2 metrics you may not have heard of but influence both SEO and site conversion.

TTFB: Time to First Byte

This metric measures the time it takes for a browser to receive the first byte from a Web server when requesting a given URL, an indicator of back-end performance.

TTI: Time to Interact

A new metric coined by Radware, time to interact refers to the point in which a page displays its primary interactive (think clickable) content, rather than full-page load.

Why do these metrics matter?


Research by Moz and Zoompf found a correlation between speedier time to first byte and higher search rankings. Yes, correlation does not equal causation—but consider the same study found that the time to load the full HTML did not correlate with better search rankings. The researchers surmise the reason TTFB may factor in search ranking is because Google crawlers can easily measure TTFB, whereas measuring the full-page load is better handled by a full browser. Also, load times can vary across browsers due to their own rendering capabilities, aside from how well a website is optimized for performance. Thus TTFB may be a more reliable indicator of positive user experience to Google.

These findings suggest it’s really about how quickly servers and back-end infrastructure can deliver Web content, not front-end website performance, that really matters when it comes to SEO advantage.

What influences TTFB?

From Moz:

  • Network latency between a visitor and the server.
  • How heavily loaded the Web server is.
  • How quickly the website’s backend can generate the content.

Tuning the backend is just as important as optimizing your HTML. Moz community member Billy Hoffman of Zoompf has written an excellent tutorial on how to determine your TTFB with tips on how to tune your backend.


Conversion rates increase when bounce rates decrease, if for nothing else than more customers stay on your site. Time to Interact is a key indication of your site’s ability to provide a good user experience and reduces perceived page load time, serving as a good measure of real-user performance.

Radware tested load times of the Internet Retailer Top 500 and found a strong correlation between pages that had a faster time to interact (TTI) and overall page load speed. However, there were a few exceptions like Neflix, iHerb and LivingSocial, which appear to have optimized their sites so primary content loads first and secondary resources, like social sharing buttons and Javascript tags, load last.

The median TTI for top 500 retailers is 4.9 seconds—well above the perceived page load threshold of 2 seconds. A study by Akamai found in 2006 that 25 percent of visitors would abandon a site that took longer than a perceived 4 seconds to load, a threshold cut in half by 2009, with 50 percent of visitors saying they bail at the 2-second mark. Only 8 percent of top-100 sites in the Radware study achieved a sub-2-second TTI.

In 2010, Strangeloop Networks (now part of Radware) founda site that loads in 3 seconds can expect 22% fewer page views, a 50% higher bounce rate, and 22% fewer conversions than a site that loads in 1 second, while a site that loads in 5 seconds experiences 35% fewer page views, a 105% higher bounce rate, and 38% fewer conversions.”

Tuning the front-end for faster TTI

As hinted by the Netflix, iHerb and LivingSocial examples, the best practice is to optimize your pages to load important, interactive content first, and defer the less important.

  • Load what’s above the fold first
  • Load interactive elements quickly
  • Defer loading scripts that support user actions that aren’t useful until after the page has fully loaded (e.g. drag-and-drop or comparison functionality)
  • Defer loading third-party scripts like analytics, social sharing
  • Use AJAX to load additional page content when the user requests it, rather than loading it up front
  • Leverage a CDN (content delivery network)
  • Compress text and images, minify code and resize or reformat media
  • Use keepalives

Your site performance is a mix of front-end and back-end optimization, but simply measuring and tuning for page load speed misses the opportunity to improve Time to First Byte and Time to Interaction, both of which have real impact on search bots and site visitors.

Reprinted by permission.

Image credit: CC by zenera


About the author: Linda Bustos

As Director of Ecommerce Research at Elastic Path, Linda Bustos works with some of the world’s largest companies to help improve conversion rates and profitability on the Web. In addition to writing the Get Elastic blog since 2007, Linda’s articles have appeared in Mobile Marketer, CMO Magazine, E-Marketing + Commerce, and Search Marketing Standard. She is a frequent speaker at industry events, including XCommerce, Conversion Conference, and Affiliate Management Days.

In 2010, Linda earned a spot on the DMNews Top 30 Direct Marketers Under 30 list. She has served as faculty for the Banff New Media Institute’s Career Accelerator Program and Marketing Profs University, and has appeared as one of the Top 100 Influential Marketers of the year in 2008 and 2009. Prior to joining Elastic Path, Linda worked agency-side, specializing in usability and SEO.

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