Why Your Ecommerce Site Is Slow — And How to Fix It (2025 Guide)
For weeks, we’ve been talking with a very large ecommerce company in the region that sells footwear and apparel. Their problem was very clear:
“Our website is slow. We’ve had this problem for months—maybe years—and we want to fix it from the root.”
This is a very common problem in this sector. So today, we bring you a complete guide for ecommerce owners, managers, and designers about why this happens and how to fix it (or defend yourself from predatory service providers), regardless of the platform.
To understand this without being repetitive, we need to clarify that websites initially were just HTML, CSS, JS files, images, SVG icons, etc. in a folder (and in essence, they still are). When someone connected to an IP or domain, a system called a “web server” sent those files, the browser received them and displayed them on the screen. That’s how websites work, in fact.
Over time and with new needs, layers were added to this system allowing server-side logic and database connections, meaning the server can send or inject data into those files before sending them. Eventually, ready-to-use solutions were created that abstract all this and are friendlier for clients who need these systems for their businesses or need something quick to build on (PaaS: Platform as a Service).
With that in mind, let’s break down the specific problems. Please read all points as each is very important:
Reason 1: Too many products per page.
Many ecommerce sites want to show their entire catalog to catch the eye and make customers buy, but we should analyze if this is really relevant for the user experience or if customers go directly to the section they want. This is first because it affects everything below to some extent, and a finer analysis is needed to find the real bottleneck. More than 50 products per page is a lot.
“My ecommerce has 800 shoes.”
In this case, pagination is needed: 20–50 products per page is ideal. You can load products manually per page or automatically as the user scrolls, though the latter takes more time technically.
Reason 2: Heavy and poorly managed images.
For banners/sliders, especially in fashion, one 1MB image might be acceptable, but product images should be kept under 250KB (preferably less). To balance good appearance and performance, we divide images into two categories:
- Thumbnails: Small images seen in listings.
- Main images: Large images both in canvas and size.
A product’s main image in a product list might be 60x60, 100x100, or 300x300 (depending on thumbnail size), while on the product page the large image might be 1000x1000 or more.
Who handles this? Neither photographers nor designers should handle this. Usually, content managers (CMS: Wordpress, Shopify, Tiendanube) and CDNs (Content Delivery Networks) include this by default. Any technician / developer can implement and automate this in a couple of hours.
Example URLs:
example.com/images/product-1.jpg
example.com/images/product-1.jpg?width=1000&height=1000
example.com/images/product-1.jpg?width=300&height=300
Yes, it’s almost magic. The system transforms the 1000x1000 image to 300x300 and caches it for later use.
Reason 3: Images vs device limitations.
Related to the previous point, ecommerce sites are usually designed with fixed sizes, meaning all web content might be in a 1280px-wide container, and product images occupy 300x300px. If the browser sends 1000x1000 images but displays them in a 300x300 space, it must resize the pixels somehow. Multiply this by 50 images, and it becomes a big problem for browsers and devices (especially mobiles), consuming lots of resources. Ideally, for a 300x300 space, send 300x300 images.
Reason 4: Images and bandwidth.
50 products means 50 images. If they are heavy, e.g., 500KB each, that’s 25MB the server must send every time someone reloads the page. Multiply this by users and it becomes huge. Bandwidth, especially on low-quality services, is like a water pipe—it has a max capacity. Optimizing image size is key.
Reason 5: Images lack lazy loading.
When a browser requests a website, it receives files, reads them, then paints the page. If it has to download 50 images at once, this competes with other critical files for initial load or functionality. Lazy loading tells images: “Don’t download until needed,” prioritizing critical images like logos or banners. It sounds complex, but it’s easy and built into modern browsers—you only need to add a simple attribute to your HTML images:
From: <img src="/product-281.jpg">
To: <img src="/product-281.jpg" loading="lazy">
It’s magic. You reduce initial downloads from 50 images to maybe 2–5.
Reason 6: Caching images and database queries.
This is more technical. Usually, platforms handle this, but it’s worth mentioning because your site might be 1 in 10 that doesn’t. When a browser requests an image, the server looks for it on disk and sends it. Disk lookup is slow, so images are cached in RAM, which is much faster. The same applies to database queries: instead of requesting “the last 5 products sorted this way” every time, you request once, store it in memory, and retrieve it on future requests.