iPhone Viewport Sizes
Common iPhone CSS viewport widths and a practical way to choose iPhone test sizes for responsive QA.
4 min read - Updated 2026-05-13
Use this guide as a compact release reference, then validate the same breakpoints in Sizzy with synchronized devices and screenshot evidence.
Cover compact and modern iPhones
Most iPhone responsive issues are caught by testing compact, common, and large-width classes instead of trying every model individually.
320px for legacy compact iPhone layouts
375px for common compact mobile behavior
390px and 393px for modern default iPhone widths
430px for large iPhone layouts
Do not ignore browser height
Viewport height changes with browser chrome, install banners, keyboards, and sticky app UI. Pages with forms, sticky CTAs, or full-screen panels need height-specific review.
Open mobile navigation with browser chrome visible
Focus form fields to trigger the keyboard
Check sticky CTA placement after scrolling
Retest any full-height sections in landscape if supported
Release checklist
Test at least 375px, 390px, and 430px widths.
Include the smallest supported width for dense pages.
Check forms with the mobile keyboard open.
Confirm navigation and CTA tap targets remain reachable.
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