How Page Speed Affects Ecommerce Conversions (With Data)

One extra second of load time costs the average ecommerce store 7% of conversions. That’s not a theory. It’s a finding from a Deloitte study of 37 leading retail and travel websites, and it holds up across a decade of research.

The math is uncomfortable. If your store converts at 2% with a 3-second load time, a 4-second load time puts you at roughly 1.86%. That’s a 7% revenue drop from one second you probably haven’t noticed.

Most ecommerce operators know page speed matters in the abstract. Fewer have measured their actual numbers or know which performance problems cause the most conversion damage. This guide covers both.

What the Data Actually Shows

The speed-conversion relationship is well-documented:

Deloitte (2020): A 0.1-second improvement in site speed improved conversion rates by 8% for retail sites. Mobile impact was even higher.

Google/SOASTA research: Pages that load in 1-3 seconds have a 32% higher probability of bounce compared to a 1-second load. At 5 seconds, that probability increases to 90%.

Portent (2019): The highest ecommerce conversion rates occur on sites that load in 0-2 seconds. Each additional second of load time between 0-5 seconds reduces conversion rates by an average of 4.42%.

Amazon’s internal research (often cited, rarely sourced directly): Every 100ms of latency cost Amazon 1% in sales. At Amazon’s scale that’s a significant number, but the proportional impact applies at any size.

The pattern is consistent: faster sites convert better. The relationship is not linear (going from 10 seconds to 9 seconds does not have the same impact as going from 2 seconds to 1 second), but for most ecommerce stores with load times between 3-7 seconds, shaving time off the load delivers measurable conversion improvement.

Core Web Vitals: What Matters for Ecommerce

Google introduced Core Web Vitals in 2021 as a set of user-centric performance metrics. Three metrics define the current standard:

Largest Contentful Paint (LCP): How long until the largest visible element (usually a hero image or product photo) finishes loading. Target: under 2.5 seconds.

First Input Delay (FID) / Interaction to Next Paint (INP): How quickly the page responds when a user taps or clicks. Target: under 200ms for INP (FID target was 100ms; INP replaced FID in 2024).

Cumulative Layout Shift (CLS): How much the page layout shifts while loading. Target: under 0.1.

For ecommerce specifically, LCP and CLS are the most critical:

LCP is almost always the product image on a product detail page or the hero image on a homepage. These are the exact assets that build or break purchase intent. A slow-loading product image is a conversion killer before the customer has even read a word of copy.

CLS creates a specific ecommerce problem: price and Add to Cart button jumping. If your price renders and then shifts because an image loads below it, or if your Add to Cart button moves when a promotional banner loads above it, customers misclick. Misclicks on mobile lead to abandonment.

Mobile vs Desktop: The Gap That Matters

Mobile traffic accounts for 60-70% of ecommerce visits for most stores. Mobile conversion rates average 1-2% lower than desktop. Page speed explains a significant portion of that gap.

Why mobile is slower:

Mobile devices have less processing power than desktop
Mobile networks (even 4G and 5G) have higher latency than wired connections
Battery saving modes throttle performance
Mobile browsers handle JavaScript differently than desktop browsers

Why this creates disproportionate conversion impact on mobile:

Mobile users have shorter patience for slow loads (they are often multitasking or in transit)
The cost of a slow mobile experience compounds with small screen UX issues
A product page that loads in 2 seconds on desktop often loads in 4-5 seconds on a mid-range Android phone

If you test your site speed only on your MacBook Pro connected to office WiFi, you are testing the experience almost none of your customers actually have.

Use Google’s PageSpeed Insights with a throttled mobile connection as your baseline. That number is your real mobile performance.

The Speed-Conversion Stack: Where to Look First

Not all performance problems have the same conversion impact. Fix these in order:

1. Server response time (TTFB) Time to First Byte is how long your server takes to respond before the browser can start rendering anything. If TTFB is over 600ms, no amount of frontend optimization will make your site fast. This is a hosting or infrastructure problem.

Acceptable TTFB: under 200ms for most ecommerce use cases. Over 600ms requires a hosting change, not a code change.

2. Render-blocking resources CSS and JavaScript that loads in the <head> of your pages blocks the browser from rendering anything else until it finishes. Most ecommerce themes include unnecessary render-blocking scripts.

Check Google PageSpeed Insights’ “Eliminate render-blocking resources” section for your specific pages.

3. Unoptimized images Product images are the heaviest assets on most ecommerce pages. Common problems:

Images served as PNG or JPEG instead of WebP (25-35% larger file size for no quality benefit)
Images sized at 3000px wide when they display at 800px
Images without lazy loading (all images loaded on page load instead of as the user scrolls)

Fixing image optimization alone typically improves LCP by 30-50% on image-heavy pages.

4. Third-party scripts Every third-party script you add (chat widgets, tracking pixels, retargeting scripts, review widgets) adds external network requests that slow your page. Each one is outside your control.

Audit your third-party scripts the same way you’d audit plugins: list them, identify which ones are actively generating business value, remove the rest.

The European Accessibility Act Performance Connection

The European Accessibility Act (EAA), enforceable from June 28, 2025, requires ecommerce services sold to EU consumers to meet WCAG 2.1 AA accessibility standards. Performance is directly connected.

WCAG 2.1 Success Criterion 2.4.3 (Focus Management) and related criteria require that pages be operable without timing out unexpectedly. Slow pages that time out or lose state mid-session create accessibility failures for users with motor disabilities who type slowly, users with cognitive disabilities who need more time, and users on assistive technologies that interact with the DOM more slowly.

Performance is not separate from accessibility. It is part of the same obligation.

The full European Accessibility Act compliance guide covers what EAA requires for Dutch and EU ecommerce stores.

When to Optimize vs When to Redesign

Performance optimization and site redesign are different interventions for different problems.

Optimize when:

Your load time is 3-6 seconds and you have identified specific fixable causes (large images, render-blocking scripts, slow TTFB)
Your Core Web Vitals are failing specific criteria but your overall site architecture is sound
You are running on a modern theme with performance in mind

Redesign when:

Your site is running on a legacy theme from 2015 with 50 plugins and a 9-second load time
Your CLS score is poor because your layout was built without performance considerations
Every optimization fix is fighting against the underlying architecture

The distinction matters because optimization has clear ROI. You measure before, apply a fix, measure after. Redesign is a larger investment with a longer return horizon.

If your performance problems are architectural, optimization is temporary patching. A redesign (or at minimum, a theme migration to a performance-first framework like Hyva for Magento or a headless stack) is the real fix.

The Hyva theme guide covers how performance-first theme architecture affects conversion in practice.

Measuring Before You Fix

The only way to know if a performance change improved conversions is to measure before and after. This sounds obvious. Most teams don’t do it.

Before making any speed changes, record:

Current conversion rate (total, and split by mobile vs desktop)
Current Core Web Vitals scores (use Google Search Console, not just PageSpeed Insights)
Current average page load time by device category

Then change one thing at a time. Image optimization is a clean test. Changing hosting, minifying JavaScript, and switching CDN simultaneously makes it impossible to know which change caused the improvement.

The ecommerce SEO audit guide covers how to integrate performance measurement into a broader revenue audit rather than treating it as isolated technical work.

The Practical Priority List

If you are overwhelmed by the number of variables, start here:

Check your hosting. Run TTFB on your homepage. If it is over 600ms, fix hosting before anything else.
Run PageSpeed Insights on mobile. Get your actual mobile LCP score.
Audit your images. Are product images served as WebP? Are they appropriately sized? Is lazy loading enabled?
Check your third-party scripts. Remove anything that does not directly generate measurable business value.
Measure Core Web Vitals in Google Search Console. Not PageSpeed Insights lab data. Real user data from your actual visitors.

These five steps, applied in order, cover the majority of performance problems that cost ecommerce stores conversions. The advanced optimizations (service workers, edge caching, code splitting) matter at scale. Start with the basics first.

What to read next

Page speed is one input into conversion rate. A fast site with poor product pages or a broken checkout still converts badly.

Before investing in performance optimization, benchmark where your conversion rate stands. E-commerce Conversion Benchmarks Europe 2025 breaks down conversion by device and traffic source, so you know whether speed is your bottleneck or if the real issues are further down the funnel.

The Ultimate Guide to Conversion Rate Optimization - the full conversion picture beyond just performance
Top 12 Checkout Optimization Tips - the checkout friction that costs you conversions regardless of load time
European Accessibility Act Compliance Guide - EAA requirements relevant to performance and accessibility

Struggling to identify where your store loses conversions? Our UX research service runs structured diagnostics across performance, UX, and conversion barriers.