BDConf: Guy Podjarny presents Performance Implication of Mobile Design

In Performance Implication of Mobile Design, Guy Podjarny (@guypod) discusses performance best practices for dedicated mobile sites and responsive designs.

Performance Matters

  • Web users will typically wait about 2-3 seconds for a site to load. Research shows if the users can’t load a page quickly, they’ll abandon ship and head to the competition.
  • Mobile users have same expectations as desktop users. They want sites to load as fast if not faster than desktop sites.

Performance for Separate Sites

  • Dedicated mobile websites cause redirect problems, which are extremely costly for performance.
  • ESPN’s dedicated mobile site redirect caused a delay of 1.3 second, and that’s before any content begins to download
  • Javascript redirects are much slower than server-side redirects. Avoid using client-side redirects for mobile detection.
  • Redirects burn up the 2-3 second frame you have to gain a user. You’ve already lost them by the time the page actually starts to load.
  • Minimize redirects. Use HTTP redirects, not JS redirects. Cache HTTP Redirects on the CDN. HTTP 301 Redirects w/ a future Expiry.

Performance for Responsive Designs

  • Responsive sites typically download a lot more content than you need.
  • 50%-90% of responsive sites had little to no performance savings on small screens than on large screens
  • Only 3% of responsive sites had a much smaller performance footprint on small screens than on large screens
  • Smashing Magazine has a rich sidebar with a lot of ads and content, and gets hidden for small screens. However, hidden content still gets downloaded.
  • Avoid using display: none; to hide content for smaller screens in responsive designs. The content still gets downloaded even though it’s not being used.
  • Media queries don’t prevent CSS downloads
  • Separate CSS files per media type typically get downloaded by browsers even if it doesn’t meet the criteria.


  • About 350K of roughly 520K of a page load is taken up by image downloads. One of the best things you can do is implement an adaptive image solution.
  • Your responsive site should match the file size of a dedicated mobile site. Build mobile first then enhance from there
  • Enhance via Javascript: Split your files by layout and resolution and progressively enhance based on the capabilities device
  • Measure your results. Without measuring all this is meaningless

One Comment

  1. Thx for keeping us up to date. Wish I was there.

    Extremely valid points on the RWD part! Even if such designs are not considered “real RWD” by experts, that is the actual current state of _trying_ to do RWD in the wild… … which need to be addressed.

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