A photo straight off your phone is thousands of pixels wide. Your website shows it a few hundred pixels wide on a phone screen, and the visitor downloads every one of those pixels anyway. That gap is the first thing to check when your site drags.
Your camera makes a photo far bigger than the page needs
Apple’s tech specs page for iPhone 16 lists a 48MP Fusion main camera with “support for super-high-resolution photos (24MP and 48MP)”. That page carries no update date. A 24 megapixel photo in the normal 4:3 shape works out to roughly 5,600 pixels across. A 48 megapixel one lands near 8,000.
Now look at the space that photo actually gets. The HTTP Archive Web Almanac’s 2024 Media chapter, published December 29, 2024 and updated January 2, 2025, measured how wide images end up inside real page layouts. On mobile, the widest single image on a page was 330 CSS pixels at the median and 392 pixels at the 90th percentile. Phone screens pack in extra pixels, so triple that for a sharp picture. You still land near 1,000 to 1,200.
Google’s web.dev guide “Image performance”, last updated November 1, 2023, states the same math plainly. A 1,000 pixel image inside a 500 pixel box “is twice as large as needed”. On a screen at triple density, that same 500 pixel box wants 1,500 pixels and no more.
So the photo off your truck is often four or five times wider than the page will ever use. The extra pixels are not visible. They are just download time.
How many bytes photos really cost
Here are numbers you can go and check. The Web Almanac’s 2025 Page Weight chapter, published January 15, 2026 and updated January 16, was built on a July 2025 crawl of the web. The median mobile home page loaded 911 KB of images. Desktop loaded 1,059 KB. At the 90th percentile, a mobile home page pulled 6,288 KB of images.
The 2024 Media chapter breaks that down per picture. The median image on a mobile page weighs 12 KB, which sounds harmless. The problem is the big one. The heaviest single image on a mobile page was 135 KB at the median, 404 KB at the 75th percentile, and 1,002 KB at the 90th. On a plumbing or roofing site, that heaviest file is almost always the shot at the top of the page, which is why a plumbing page has to be built light for a phone.
The same chapter found the median mobile page carries 13 image elements. Thirteen photos, one of them huge, is the normal shape of the problem.
Find the heavy ones on your own site
If you have read older advice about this, it told you to look for an audit called “Properly size images”. That name is gone. The Chrome for Developers page for it, last updated May 2, 2019, now opens with a warning: “This audit has moved into the Improve image delivery insight as of Lighthouse 13.”
“Improve image delivery” is the name to look for today. Its own Chrome for Developers page, published October 8, 2025, says the check “highlights images that have unnecessarily large download sizes”, and sets the floor for what gets reported: “Any images with estimated byte savings less than 4 KiB won’t be flagged.”
Run PageSpeed Insights on your own page and read the mobile tab. Scroll past the score to the list of insights. Open “Improve image delivery”. It names the exact files and the bytes you would save on each one. Write down the three worst.
That list is the whole job. You are not guessing which photo is the problem. Google has already named it.
Resize first, then change the format
Resizing and re-saving are two different fixes, and the order matters. Saving a 5,600 pixel photo in a newer format still leaves you a 5,600 pixel photo.
- Resize the file first. A rule of thumb, not a measured finding: photos on a trade site rarely need to be wider than about 2,000 pixels, and thumbnails need far less. A full-width desktop hero is the one exception worth going bigger on.
- Then save it as WebP or AVIF. The web.dev guide above says tests have shown AVIF giving “greater than 50% savings when compared to JPEG in some cases”. Read that hedge. Some cases, not all of them.
- Then re-upload and run the test again. If the mobile score moves after the swap, do the next three files.
The web has been slow to move here. The 2024 Media chapter found JPEG fell from 40% of all images in 2022 down to 32% in 2024. Most sites are still shipping the old format at the old size.
The photo at the top counts most
Google’s page on Largest Contentful Paint, updated September 4, 2025, says sites “should strive to have Largest Contentful Paint of 2.5 seconds or less”, measured at the 75th percentile of page loads. On a trades site, the thing being measured is nearly always your hero photo.
Two rules for that top photo. Do not lazy load it. The 2024 Media chapter found lazy loading now runs on a third of all websites, and that 9.5% of the images responsible for Largest Contentful Paint on mobile were lazy loaded anyway. The chapter calls that an anti-pattern that makes pages slower. Lazy load the gallery further down instead.
Second, set width and height on every image. The same chapter found only 32% of image elements on mobile had both set. That one is about the page jumping rather than the page being slow, and it has its own page here: why your page jumps just as someone taps the phone number.
What this will not do, and what to do this week
Be careful with the numbers above. The Web Almanac crawls the web at large, not US plumbing, roofing, HVAC and electrical sites. Your own page may be far lighter than the median, or several times heavier. The only figure that describes your business is the one from your own test.
Resizing photos is free. You do not need to hire anyone for it, and if PageSpeed does not flag your images, leave them alone and go fix something else. Smaller photos will not move you up in search on their own, will not make the phone ring, and will not fix a slow host or a heavy page builder. There are no client case studies here to wave at you. The only site to point at in full is this one, which scored 100 on Google’s PageSpeed test on desktop and mobile, when it launched in August 2026.
Plain steps:
- Open PageSpeed Insights on your phone and test your busiest page.
- Write down the mobile score before you touch anything.
- Open “Improve image delivery” and note the three heaviest files.
- Resize each to about 2,000 pixels wide or less, save as WebP, re-upload.
- Re-test and compare the score to what you wrote down.
If the photos were the whole problem, you will see it in one afternoon. If the score barely moves, the weight is somewhere else, and what actually makes a website load faster, in order walks through the rest of the list. If you would rather the resizing and the formats be handled at build time so nobody has to remember, that is part of how these sites get built.