Designing for One-Handed Use on Larger Phones
Thumb-reach heatmap studies, and our own usability sessions filming users holding a 6.7-inch phone one-handed, consistently show the top third of the screen sitting in what's commonly called the 'hard' zone — reachable, but requiring a hand shift or grip adjustment that most users simply won't bother making mid-task. For a food delivery app redesign, we found the original design had put the primary 'place order' action in the top-right corner, exactly where one-handed reach is worst for right-handed users holding the phone naturally, let alone left-handed ones.
The fix was moving primary actions toward the bottom third of the screen wherever the interaction model allowed it. We restructured the checkout flow to use a persistent bottom action bar for the primary CTA instead of a top nav bar button, and moved from a top tab bar to a bottom tab bar for primary navigation, matching where a thumb naturally rests when gripping the phone one-handed.
For content that genuinely needs to live at the top of the screen — search bars, filters — we leaned on native reachability affordances rather than fighting the geometry: pull-to-reveal patterns, and on iOS, respecting the system Reachability gesture by making sure our custom navigation bars didn't override or break that system behavior, which we found one earlier build had accidentally done by intercepting touch events at the top of the screen.
Gesture-based actions got a deliberate secondary path for reachability too. A swipe-to-archive action on a list required a full-width swipe gesture that's awkward one-handed on a large phone; we added a smaller, thumb-reachable action button as an alternative to the gesture rather than requiring the swipe, since usability testing showed a meaningful number of users simply weren't attempting the gesture at all on larger devices.
None of this shows up well in a static Figma mockup, which is part of why it gets under-prioritized in design reviews — a screenshot doesn't convey reach difficulty. We started including a simple annotated reach-zone overlay on key screens during design review specifically to force the conversation before implementation, rather than discovering the problem in usability testing after the screens were already built.
