Mobile & UX

Thumb Zone

The part of a phone screen a thumb reaches comfortably one-handed.

The thumb zone is the area of a phone screen a thumb can reach comfortably while holding the device in one hand — roughly the lower two-thirds, with the top corners hardest to reach. It is why primary actions belong at the bottom of a mobile layout rather than in a top corner, where they were placed by desktop convention.

Definition

Research on one-handed phone use maps the screen into an easy arc within the thumb's natural sweep, a stretch zone, and a hard-to-reach region in the far top corner. Screens have grown, so the hard region has grown with them.

The practical consequence is placement rather than size: bottom navigation, action buttons within the lower arc, and destructive actions deliberately outside it.

Why It Matters

Most traffic is mobile and most mobile use is one-handed. A primary call to action in the top-right corner is asking for a grip change on every interaction.

Example

iOS moved Safari's address bar to the bottom of the screen for exactly this reason. A "Buy" button pinned to the bottom of a product page is the same idea.

The zone moved because phones grew

The original thumb-zone research was done on screens under four inches, where most of the display was reachable. Phones are now six inches and taller, and the unreachable region has grown with them: the top corners of a modern phone require either a grip change or a two-handed hold.

This is why platform conventions moved. Bottom navigation bars, pull-to-refresh, and iOS putting Safari's address bar at the bottom are all responses to the same measurement. A design that puts the primary action in the top-right corner is following a desktop convention on a device where that corner is the hardest place to reach.

The practical rule: primary actions in the lower half, destructive actions deliberately outside the easy arc, and nothing critical in the top corners.

How SlapMyWeb checks this

The audit measures tap target sizes and the spacing between adjacent ones against the WCAG 2.2 target-size criterion, and reports elements too small or too close to hit reliably. It cannot judge where on the screen an action sits relative to a thumb — that is a design decision — so it reports the measurable half and leaves placement to you.

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