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Gallery Thumbnail Placement: Left or Below A/B Test

Vertical and horizontal thumbnail strips divide the gallery area differently.

  • Product page
  • Add-to-cart rate

Variant A vs Variant B

Where it sits is the variable; the element itself does not change.

Changed
Placement
Page
Product page
Difference
moved

Hypothesis

This can change both which thumbnails are visible and the space left for the main image. Compare two fixed layouts and interpret the connected size changes as part of the layout, not as position alone.

How to run this test

Primary metric

Add-to-cart rate

Compare successful add-to-cart events per assigned visitor across the two gallery layouts.

Other metrics

  • Gallery interaction rateCheck whether more visitors inspect multiple images.
  • Images viewedMeasure actual image visibility; fewer views are not automatically worse.
  • Purchase conversion rate (CR)Compare purchases per assigned visitor.
  • Return rateTrack returns over the same follow-up period.

What to check before and during the test

  • PlacementCompare vertical thumbnails on the left with horizontal thumbnails below; the result applies to the layout as a whole.
  • VisibilityRecord how many images are visible without scrolling.
  • Main image sizeRecord the main image area in each layout; this difference is part of the layout change.
  • DiscoverabilityReview gallery interactions and usability feedback.
  • DeviceAnalyze devices where the layouts differ and report their results separately.

Setup mistakes to avoid

  1. 1Treat thumbnail placement and main-image size as one combined layout choice in this test.
  2. 2Do not make thumbnails too small to tap.
  3. 3Keep the number of images unchanged.
  4. 4Preserve keyboard navigation through the gallery.
  5. 5Do not apply the desktop result to the mobile gallery.