Over half of web traffic is mobile. For many SaaS products, the percentage of signups that start on a mobile device is even higher — someone sees a tweet, taps a link, decides to sign up on the spot.
And most SaaS products treat mobile as a secondary experience. The result is that a significant percentage of their most motivated potential customers hit a broken or frustrating flow and leave.
This guide walks through how to run a proper mobile UX audit — what to look at, what good looks like, and how to prioritise what to fix.
Test on a real device. Browser dev tools in "mobile mode" are useful but not sufficient. They don't replicate real touch input, real network conditions, real font rendering, or the thumb-reach problem.
Test on at least two real devices: a current-model iPhone and a mid-range Android (the kind your actual users have, not a flagship). Your target market in Southeast Asia or India is likely on a device that's 2–3 years old. Test on that.
Test on real network conditions. Most mobile users are on 4G, not WiFi. Chrome DevTools network throttling lets you simulate this. Set it to "Fast 4G" as your baseline test.
Test in portrait orientation first. Most mobile usage is portrait. Make sure the product works correctly in portrait before worrying about landscape.
Mobile performance is directly tied to conversion. Google's research shows that 53% of mobile users abandon a page that takes more than 3 seconds to load.
Check these metrics using Google PageSpeed Insights (mobile tab):
Largest Contentful Paint (LCP): How long until the main content is visible? Target: under 2.5 seconds.
Cumulative Layout Shift (CLS): Do elements jump around while the page loads? Target: below 0.1.
Time to Interactive (TTI): How long until the page is actually usable? Target: under 3.8 seconds.
Total page weight: Under 1MB is excellent, under 2MB is acceptable, over 3MB is a problem on mobile.
Common causes of mobile performance problems: uncompressed images, too many third-party scripts (chat widgets, analytics, ad trackers), unoptimised web fonts, and large JavaScript bundles.
Tap through your entire product with your actual thumb — not with a precise stylus tap or a mouse click.
Minimum size: Apple's HIG recommends 44x44pt. Google's Material Design recommends 48x48dp. Anything smaller is genuinely difficult to tap accurately, especially for users with larger hands.
Minimum spacing: Interactive elements should have at least 8px of space between them. Links in a dense nav menu, small icon buttons grouped together, or form action buttons placed side by side are common failures.
Bottom vs top placement: The thumb's natural reach on a phone covers the bottom half of the screen most easily. Critical actions (primary CTA, submit button, back/next in flows) should be reachable without shifting hand grip.
Forms are where most mobile UX debt lives.
Trigger the right keyboard. Every input field should have the correct input type:
Most SaaS signup forms fail this. The result is a full text keyboard for an email field, which is more cumbersome than necessary.
Test what happens when the keyboard appears. On small screens, the software keyboard can cover up to 40% of the viewport. If your submit button or a key field is in the bottom half of the screen, it will be hidden by the keyboard when a user is filling in the field above it.
Walk through your forms with the keyboard open. Is everything still accessible?
Label visibility. Placeholder text disappears when users start typing. Every field needs a persistent label above it, not just placeholder text inside it.
Does the mobile nav work? If you have a hamburger menu, does it open reliably? Are the items inside it large enough to tap?
Can a user complete the primary flow with one hand? The one-handed usage test: hold your phone in your dominant hand and try to navigate your product using only your thumb. Where do you have to shift your grip? Those are friction points.
Is there a fixed bottom navigation for key actions? For products that users navigate frequently (dashboards, apps), a fixed bottom navigation bar puts key destinations in easy reach. Top navigation bars require a two-handed or full-arm reach.
Does the back button work as expected? The hardware/software back button is a primary navigation tool on Android. If your single-page app breaks it, Android users will be frustrated.
Font size. Body text should be at least 16px. Smaller than this requires users to pinch to zoom, which is a signal that the product isn't designed for mobile reading.
Line length. Text lines that are too long (over 70 characters) are hard to read on a small screen. For mobile, aim for 45–60 characters per line.
Does content reflow correctly at different widths? Test at 320px (small phones) and 390px (iPhone 14 Pro). Common failures: tables that don't scroll horizontally, code blocks that overflow, side-by-side content that doesn't stack.
Walk through your full signup and onboarding flow on mobile, timed.
Ask at each step:
Note the total time from landing page to completed signup. If it takes more than 3 minutes on mobile, you have drop-off risk.
A proper mobile UX audit across all these dimensions produces a score for each area. Look for patterns — if performance is 30/100 but everything else is above 70, you have a clear priority. If touch targets are failing across the board, that's a design system issue, not a one-page fix.
UXAuditPro covers mobile UX as one of seven scored audit dimensions. Running a quick audit before your next release is a good way to surface mobile issues your team may have missed during desktop-first development. First audit is free.
Related reading: UX audit checklist — 47 things to check before your next launch
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