Speed Up WordPress With Image Optimization
If you want to speed up WordPress with image optimization, the fastest way to understand why it matters isn’t reading another generic checklist; it’s looking at real numbers from a real site. So that’s what I’m doing in this post.
I ran my own site through Google PageSpeed Insights and got two results that told me exactly where my speed problem was coming from. My mobile Largest Contentful Paint (LCP) came back at 6.6 seconds, well above Google’s recommended target of under 2.5 seconds. And under the opportunities section, “Improve image delivery” was flagged with an estimated 221 KiB in potential savings on desktop.
This post isn’t a general “how to make WordPress faster” guide. I’ve already written that one. This is narrower and more useful than that: I’m going to show you the exact metrics that pointed to images as a problem on my own site, explain what those metrics actually mean, and walk through what I did about it, including the workaround I use once I run out of free compression credits.
If you’ve never actually looked at your own PageSpeed report, or you’ve looked at it and had no idea what half the terms meant, this post is for you.
Why I'm Writing This as a Case Study, Not a Tutorial
I want to be upfront about what this post is and isn’t.
It’s not a step-by-step “here’s how to optimize every image on your site” tutorial; I cover that in How to Optimize Images for WordPress. It’s also not a broad overview of every speed factor on a WordPress site; that’s How to Speed Up WordPress.
This post has one job: to prove, with my own audit data, that images and site speed are directly connected and to show you how to find that connection on your own site using the same free tool I used.
I think this matters because a lot of “speed up your site” advice online is theoretical. Nobody shows you their actual numbers. I’m showing you mine.
My Real PageSpeed Insights Results
Here’s exactly what I found when I ran my site through PageSpeed Insights.
Mobile LCP: 6.6 seconds. Google’s benchmark for a “good” LCP is under 2.5 seconds. My mobile score wasn’t close; it was more than double the “needs improvement” range and well into “poor.”
Desktop opportunity: “Improve image delivery,” estimated savings of 221 KiB. This is a specific line item PageSpeed Insights generates when it detects that images on your page are larger than they need to be for the way they’re actually displayed.
I’m not sharing these numbers to be dramatic. I’m sharing them because they’re the clearest, most honest way to explain why image optimization isn’t a “nice to have”; it’s often the single biggest lever you have to speed up WordPress, with image optimization specifically, rather than more complicated fixes like server changes or code optimization.
What LCP Actually Means (In Plain English)
LCP stands for Largest Contentful Paint. It’s one of Google’s Core Web Vitals, and it measures one specific thing: how long it takes for the biggest visible element on your page to fully load and appear on screen.
On most blog posts, that “largest element” is an image, usually the featured image or a large image near the top of the post. Not your text. Not your header. The image.
So when PageSpeed Insights tells you your LCP is 6.6 seconds, it’s telling you, “The biggest thing on this page took 6.6 seconds to show up for a visitor.” That’s the point where a reader on a slow mobile connection is staring at a half-loaded page, deciding whether to wait or leave.
Google considers anything under 2.5 seconds good, 2.5 to 4 seconds needs improvement, and anything above 4 seconds poor. At 6.6 seconds, my site was sitting comfortably in “poor” territory, and LCP is a confirmed ranking factor as part of Core Web Vitals, not just a vanity metric.
You can read Google’s own documentation on how LCP is measured and scored directly on their Core Web Vitals and PageSpeed Insights page, which is also where I ran this exact test.
Why Images Are So Often the Biggest LCP Offender
This is the part that made everything click for me, so I want to explain it clearly.
A typical blog post page is made up of text, maybe a few buttons, some white space, and images. Text loads almost instantly; it’s just characters, and browsers render it fast. Buttons and layout elements are lightweight too.
Images are different. A single unoptimized photo straight out of a phone or a stock photo site can be 2, 3, or sometimes 5+ megabytes. That one file has to travel from the server to the visitor’s device before it can display. On a fast desktop connection, you might not notice. On a mobile connection, which is how most people read blog content, that delay becomes very visible, very fast.
So when PageSpeed Insights calculates your LCP, and the “largest contentful” element on your page happens to be a giant, uncompressed image, it’s basically inevitable that your LCP score reflects it. That’s the direct line between image file size and this specific metric: the bigger the file, the longer it takes to paint, the worse your LCP.
This is exactly why “Improve image delivery” showed up on my report at the same time as my poor LCP score. They weren’t two separate problems. They were the same problem, described in two different ways.
How to Run Your Own PageSpeed Insights Test (Step by Step)
Before you can fix anything, you need to see your own numbers. Here’s exactly how to do that, using the same free tool I used.
- Go to Google’s PageSpeed Insights tool. It’s free, requires no account, and no plugin install. You can access it directly at pagespeed.web.dev.
- Paste in the URL of the page you want to test. Start with your homepage or your most-visited blog post — that’s usually where speed matters most for first impressions and SEO.
- Click “Analyze” and wait for both reports to generate. PageSpeed Insights gives you two separate scores: Mobile and Desktop. Always check both — mobile is usually worse, and it’s the one Google weighs more heavily for ranking.
- Scroll to the Core Web Vitals section first. Look specifically at your LCP number. That’s your headline speed metric.
- Scroll down to “Opportunities” or “Diagnostics.” This is where issues like “Improve image delivery,” “Properly size images,” or “Serve images in next-gen formats” will show up if images are a problem for you.
- Note the estimated savings next to each opportunity. PageSpeed Insights will actually tell you, in KiB or seconds, roughly how much you’d gain by fixing each issue. This is what gave me my 221 KiB number.
- Re-run the test after making changes. This is the only way to actually confirm whether what you did worked. Don’t guess, measure.
That’s it. No plugin, no login, no cost. Anyone reading this can run this exact test on their own site in under two minutes.
How I Actually Fixed It
Once I knew images were my problem, the fix came down to two things: compressing my existing images and changing my workflow for future ones.
Compressing Existing Images
I went through my media library and compressed my largest, most-used images, starting with the ones on my highest-traffic posts, since those matter most for both user experience and search visibility. Compression reduces file size by removing unnecessary data from the image file, often with little to no visible loss in quality, especially for the compression levels most blog images need.
I use ShortPixel for this. If you want my full experience with it, including what I like and where it falls short, I’ve covered that separately in ShortPixel Review (My Experience).
My Free-Plan Workaround
Here’s the honest, practical part most posts skip: ShortPixel’s free plan gives you a limited number of image credits per month. Once I hit that limit, I don’t pay for more; I switch to a manual workaround instead.
My rule is simple: I keep every image under 100kb before I upload it. To do that once I’m out of ShortPixel credits, I use free online compression tools to manually shrink images to under that 100kb threshold before adding them to a post. It’s an extra step, but it costs nothing, and it means my image sizes stay consistent even in months when I’m publishing more than my free compression credits can cover.
This isn’t a glamorous system. It’s just the actual thing I do, and it works.
On Before-and-After Numbers
I want to be straight with you here: at the time I’m writing this, I’ve applied these fixes, but I’m still in the process of re-testing and confirming the updated PageSpeed results. I’m not going to invent a “my LCP dropped to 1.8 seconds” number to make this post look tidier than it is. When I have confirmed after numbers from re-running the test, I’ll update this post with the real comparison. What I can tell you honestly, right now, is the before 6.6 seconds mobile LCP, a 221 KiB image delivery opportunity, and the specific fix I applied. The measuring is in progress, not finished.
If you’re doing this on your own site, I’d encourage you to do the same: write down your before numbers first, make your changes, then re-test. That before number is what makes the after number meaningful.
Why This Actually Matters for a WordPress Beginner
If you’re new to blogging, it’s easy to assume speed is a technical problem for developers to solve. It isn’t, at least not entirely. A huge chunk of it comes down to a habit as simple as “compress the image before you upload it.”
You don’t need to understand code to speed up WordPress with image optimization. You need to understand two things: how to read your PageSpeed report and how to compress an image before it goes into your media library. Everything else is optional extra credit.
FAQ
Does image optimization really make that much difference to site speed? Yes, on most blog and content sites, images are the single largest files loading on any given page, and often the largest visible element too, which directly affects your LCP score. Fixing images is usually the highest-impact, lowest-effort speed fix available to a beginner.
What’s a good LCP score to aim for? Google considers under 2.5 seconds “good,” 2.5 to 4 seconds “needs improvement,” and anything over 4 seconds “poor.” My mobile LCP came back at 6.6 seconds, which is why images were flagged as a priority fix on my site.
Is mobile or desktop PageSpeed score more important? Mobile matters more for most sites, since the majority of blog traffic comes from mobile devices and mobile connections are typically slower and less consistent than desktop connections. Google also weighs mobile performance heavily for search ranking.
Do I need a paid tool to optimize images for WordPress? No. Free tools can get you very far, including free compression tools and the free tier of plugins like ShortPixel. My own workaround for staying under file size limits once I exceed free plan credits relies entirely on free tools, not paid upgrades.
How often should I re-run a PageSpeed Insights test? I’d recommend testing before and after any significant change — a theme update, a new plugin, or a batch of image optimization work so you can actually confirm whether the change helped rather than guessing.
Will optimizing images fix my site speed completely? Not necessarily on its own. Images are very often the biggest single factor, especially for LCP, but other elements like hosting, caching, and plugin bloat also affect speed. That’s why I’ve covered the fuller picture separately in How to Speed Up WordPress.
Conclusion
The point of this post wasn’t to give you another generic list of speed tips; it was to show you, with my own real numbers, exactly how image size and site speed are connected. My PageSpeed Insights audit flagged a 221 KiB “Improve image delivery” opportunity on desktop and a 6.6-second mobile LCP, and both of those pointed to the same root cause: images that were larger than they needed to be.
If you take one thing from this case study, let it be this: don’t guess whether images are slowing down your site. Run the test yourself using the free PageSpeed Insights tool, look at your LCP number and your image-related opportunities, and you’ll know exactly where you stand. Then fix what you find: compress your existing images, keep new uploads under a reasonable file size, and use free tools if you don’t want to pay for a compression service.
I’ll update this post with my own confirmed after-results once I’ve finished re-testing. Until then, use my before numbers as a benchmark, run your own test, and start with whatever your report actually tells you to fix, not what a generic checklist assumes your problem is. If you want the deeper walkthroughs on either side of this process, How to Optimize Images for WordPress and How to Speed Up WordPress cover those in full.
