> ## Documentation Index > Fetch the complete documentation index at: https://docs.vortexiq.ai/llms.txt > Use this file to discover all available pages before exploring further. # Mobile vs Desktop Score, Website Performance (PageSpeed + CrUX) > Mobile vs Desktop Score for Website Performance (PageSpeed + CrUX) stores. Tracked live in Vortex IQ Nerve Centre. How to read it, why it matters, and how ... **Metrics type:** [Supporting Metrics](/nerve-centre/overview#metrics-types-explained) • **Category:** [Website Performance](/nerve-centre/connectors#connectors-by-type) ## At a glance > **Lab Performance Score side-by-side mobile vs desktop**, surfacing the gap between the two profiles. **The "are we mobile-broken" diagnostic**: mobile-first indexing means Google primarily ranks on mobile CWV, but most engineering teams develop on desktop and may miss mobile-specific issues. **Typical healthy gap**: 15-30 points (desktop higher). Larger gaps suggest mobile-specific problems (heavy mobile JS, mobile-only widgets, responsive image issues) that desktop development workflows don't surface. | | | | ----------------------------------- | ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | **What it counts** | Two Lighthouse Performance Score values from the same URL, one with mobile profile (Slow 4G + mid-tier CPU emulation) and one with desktop profile (unthrottled). Reported side-by-side with the gap. | | **Sample type** | **Lab data** from two Lighthouse audit runs (one per device profile). | | **Why this matters** | Mobile-first indexing means mobile is the priority for ranking, but engineering teams develop on desktop and may not notice mobile-specific issues. **The score gap surfaces this blind spot**: if desktop is 90 but mobile is 40, the site is fundamentally desktop-biased and mobile users (who matter most for ranking) are getting a worse experience. | | **Typical gap interpretations** | **0-15 point gap**: site is well-tuned for mobile; structural emulation differences explain the gap. **15-30 point gap**: typical for ecommerce; mobile-specific optimisation work would help but isn't critical. **30-50 point gap**: meaningful mobile-only issues; investigate mobile-specific JS, image variants, viewport handling. **50+ point gap**: mobile-broken; ranking-impact territory; urgent fix work needed. | | **Why the gap exists structurally** | (1) **Slow 4G emulation** vs unthrottled desktop network = 5-10x bandwidth difference. (2) **Mid-tier CPU emulation** vs unthrottled desktop CPU = 4x JS execution time difference. (3) **Smaller viewport** selects different LCP elements (mobile may select hero image where desktop selects header text). (4) **Mobile-specific widgets** (cart drawer, mobile menu, touch handlers) add JS only on mobile. | | **Reading the gap diagnostically** | If LCP gap is large but other metrics' gaps are small → mobile image/network issue. If TBT gap is large → mobile-specific JS or third-party cost. If CLS gap is large → mobile-specific late-loading widgets. **Each gap pattern points to a different fix focus**. | | **Currency** | n/a, two 0-100 scores. | | **Time window** | `T/7D` | | **Alert trigger** | `gap > 40 points` (mobile-broken signal). | | **Sentiment key** | `null` (comparison view). | | **Roles** | owner, marketing, operations | ## Calculation Calculated automatically from your Website Performance (PageSpeed + CrUX) data. See the At a glance summary above for what the metric tracks and the worked example below for a typical reading. ## Worked example A UK-based BigCommerce fashion store, lab measurements per template Wednesday 15 May 26. | Page template | Mobile score | Desktop score | Gap | Read | | ------------------------- | -----------: | ------------: | ------------: | ------------------------------------------------------------ | | Homepage | 42 | 76 | **34 points** | Concerning gap; mobile-specific issues | | Product detail page | 58 | 82 | 24 points | Typical gap | | Collection page | 48 | 79 | **31 points** | Concerning; collection-page filter widget JS-heavy on mobile | | Cart | 62 | 88 | 26 points | Typical | | Checkout | 71 | 92 | 21 points | Typical | | **Site-weighted average** | **51** | **81** | **30 points** | **Borderline; mobile-side work would help** | What the comparison is telling us: 1. **Site-wide gap of 30 points sits at the borderline** between "typical" and "concerning". Desktop is healthy; mobile is dragging the overall picture. **This is the textbook pattern** for ecommerce sites built without dedicated mobile performance discipline. 2. **The homepage and collection pages have the largest gaps (34 and 31 points).** Both pages have mobile-specific friction: the homepage hero carousel renders differently on mobile (4 unoptimised PNGs that are oversized for mobile viewport); the collection page's filter widget runs heavy JS that mid-tier mobile CPUs struggle with. 3. **PDPs and checkout have typical gaps (24 and 21 points)**, suggesting mobile-specific work isn't urgently needed there. The work to do concentrates on homepage + collection. 4. **The fix isn't to "make desktop slower"**, it's to lift mobile to closer parity. **Recommended optimisation focus**: * **Homepage**: image responsive variants via `srcset` (saves 1.5-2MB on mobile); defer hero video carousel for mobile * **Collection page**: virtualise filter-widget grid on mobile; debounce filter clicks; defer non-critical JS * **Estimated post-fix mobile score uplift**: homepage 42 → 65, collection 48 → 70 5. **Why this matters for ranking**: Google's mobile-first indexing primarily uses mobile CWV. **A 30-point mobile-vs-desktop gap signals mobile is the priority work**; closing it lifts ranking impact. 6. **Compare to industry**: brands that follow strict mobile-first development discipline operate at 5-15 point gaps. Brands like Shopify, Catalyst-on-BigCommerce, and modern Next.js sites often operate at \<10 point gaps because their frameworks default to mobile-friendly patterns. Stencil-themed BC sites typically run 25-40 point gaps because Stencil defaults aren't aggressively mobile-optimised. The diagnostic flow: 1. **Read the gap; classify** (0-15 healthy, 15-30 typical, 30-50 concerning, 50+ urgent). 2. **For concerning/urgent gaps**, decompose by sub-metric: which CWV has the biggest mobile-vs-desktop gap? 3. **Apply mobile-specific fix patterns**: responsive images, mobile-aware widget loading, mobile-specific JS deferral. 4. **Re-audit** to confirm the gap closes. Rapid-response playbook: | Time horizon | Action | | -------------- | ------------------------------------------------------------------------------------------------------------------- | | First 1 hour | Decompose gap by sub-metric. | | First 24 hours | Apply highest-leverage mobile fix (typically image responsive variants). | | Day 7 | Re-audit; confirm mobile score improvement. | | Day 28 | Field metrics confirm via [`crux_mobile_pass`](/nerve-centre/kpi-cards/website-performance/mobile-speed-pass-rate). | ## Sibling cards merchants should reference together | Card | Why merchants reach for it | | ---------------------------------------------------------------------------------------------------------- | --------------------------------------- | | [`psi_mobile_score_compare`](/nerve-centre/kpi-cards/website-performance/overall-score-mobile-vs-desktop) | Per-template mobile/desktop comparison. | | [`psi_mobile_desktop_lcp`](/nerve-centre/kpi-cards/website-performance/load-speed-mobile-vs-desktop) | LCP-specific device gap. | | [`psi_mobile_desktop_inp`](/nerve-centre/kpi-cards/website-performance/responsiveness-mobile-vs-desktop) | INP-specific device gap. | | [`psi_mobile_desktop_cls`](/nerve-centre/kpi-cards/website-performance/layout-stability-mobile-vs-desktop) | CLS-specific device gap. | | [`psi_mobile_desktop_ttfb`](/nerve-centre/kpi-cards/website-performance/server-speed-mobile-vs-desktop) | TTFB-specific device gap. | | [`crux_mobile_pass`](/nerve-centre/kpi-cards/website-performance/mobile-speed-pass-rate) | Mobile-only field pass rate. | | [`crux_desktop_pass`](/nerve-centre/kpi-cards/website-performance/desktop-speed-pass-rate) | Desktop-only field pass rate. | | [`psi_perf_score_summary`](/nerve-centre/kpi-cards/website-performance/performance-score-summary) | Composite score (mobile by default). | | [`psi_image_optimisation`](/nerve-centre/kpi-cards/website-performance/image-optimisation) | Common mobile-specific fix lever. | ## Reconciling against the vendor's own dashboard **Where to look:** * **PageSpeed Insights**, toggle between Mobile and Desktop tabs at the top of the report. * **Chrome DevTools → Lighthouse panel**, choose Mobile or Desktop device profile. * **WebPageTest**, supports custom device emulation including the same mobile/desktop split. **Why the Vortex IQ device gap may differ from PSI:** | Reason | Direction | What to do | | ------------------------------------------------------------------------------------------------------------------------------------------------------- | ---------------- | ----------------------------------------------------- | | **Run-to-run variance.** Each device profile has independent variance. | Either direction | Use 7-day rolling for trend reads. | | **Default profile differences.** PSI uses Google's standard mobile/desktop profiles; some Lighthouse implementations use slightly different throttling. | Small | Confirm both views use canonical Lighthouse profiles. | **Cross-connector reconciliation:** primarily internal (with mobile/desktop pass rate cards and per-CWV device gap cards). **Quick rule for support tickets:** if a merchant says *"my desktop is fast but mobile is slow, what should I do?"*, the answer is in this card's worked example, apply mobile-specific fix patterns (responsive images, mobile-aware widget loading, JS deferral on mobile). ## Known limitations / merchant FAQs **My desktop is 95 and mobile is 50. Where do I focus?** Mobile, almost always. Mobile-first indexing means mobile is the priority for ranking. Desktop being healthy is good but doesn't compensate for mobile being broken. **Apply mobile-specific fix patterns**: responsive images, mobile-aware JS, defer non-critical mobile widgets. **Why is my mobile structurally slower than desktop?** Three reasons: (1) Lighthouse mobile applies Slow 4G throttling (\~5x slower than typical desktop wifi); (2) Lighthouse mobile applies 4x CPU slowdown; (3) mobile devices in real life have less compute power than desktop machines. **Industry-typical**: 15-30 point gap between mobile and desktop scores. **Should I optimise to make mobile match desktop?** Approximately, but not exactly. Mobile-target should be 70+ score (close to desktop's 80-90 range, with the structural emulation gap accepted). **Pushing past 80 mobile score** requires architectural-level work (server-side rendering, edge functions, aggressive lazy-loading) that's typically not justified by the marginal benefit. **My BC Stencil site has a 35-point gap. Is that bad?** Concerning band. Stencil sites without dedicated mobile optimisation typically run 25-40 point gaps. **Catalyst (BC's Next.js stack) typically runs 10-20 point gaps** because it defaults to mobile-friendly patterns. **Migration is one of the strongest mobile-performance wins** alongside other Catalyst benefits. **Can I have a smaller gap by making desktop slower?** Theoretically yes; commercially absurd. The point of the gap analysis is to lift mobile, not to lower desktop. **Don't intentionally degrade desktop**; protect it while improving mobile. **Why does the gap matter if mobile is healthy at 70?** It doesn't, much. Once mobile is in healthy band (70+), the gap is informational rather than actionable. **Concerning gaps** are when mobile is in red band (under 50) while desktop is healthy, that's the mobile-broken pattern. *** ### Tracked live in Vortex IQ Nerve Centre *Mobile vs Desktop Score* is one of hundreds of KPI pulses Vortex IQ tracks across Website Performance (PageSpeed + CrUX) and 70+ other ecommerce connectors. Nerve Centre runs the detection layer; Vortex Mind investigates the cause when something moves; Ask Viq lets you interrogate any number in plain English. [Start for free](https://app.vortexiq.ai/login) or [book a demo](https://www.vortexiq.ai/contact-us) to see this metric running on your own data.