How to Convert Images to WebP in WordPress Automatically

Images are often the heaviest part of a web page. A few unoptimized JPEGs from a phone or stock site can slow your site more than all your plugins combined. The fix is simple: convert images to WebP in WordPress automatically, so every upload is smaller before it ever reaches a visitor.

This guide explains what WebP is, why it’s smaller, and how to set up a free plugin that converts and compresses on upload and in bulk. You’ll also learn how to check the results and avoid the mistakes that catch people out.

What Is WebP and Why Is It Smaller?

WebP is a modern image format developed by Google. It supports both lossy compression (like JPEG) and lossless compression (like PNG), plus transparency and animation.

According to Google’s WebP documentation, WebP lossless images are 26% smaller than PNGs, and WebP lossy images are 25–34% smaller than comparable JPEGs at equivalent quality.

Smaller files mean faster downloads, especially on mobile connections. Since images are frequently the largest element on a page, they often affect your Largest Contentful Paint (LCP), one of the Core Web Vitals.

Browser support

WebP is supported by all current major browsers, including Chrome, Firefox, Safari, and Edge. WordPress itself has accepted WebP uploads since version 5.8. For most sites today, serving WebP is a safe default.

Why Image Optimization Belongs on Autopilot

You can convert images by hand in an image editor before uploading. That works for a week. Then a client uploads a 6 MB photo straight from their phone, and your homepage crawls.

Automatic conversion fixes the problem at the source. Every image is compressed, resized, and converted the moment it’s uploaded, no matter who uploads it.

How to Convert Images to WebP in WordPress with BinsOptimizer

BinsOptimizer is a free image optimizer that works differently from most. Instead of sending your images to a cloud service, it converts and compresses them directly in your browser, before they’re uploaded to your server.

That brings a few practical benefits:

• No API key, no subscription, no limits. There's no external service to connect.
• Private. Your images aren't sent to a third-party server for processing.
• No server load. The work happens on your own machine, so it doesn't use your hosting resources.
• Instant results. Optimization happens as you upload, with no background queue.

It converts JPEG and PNG images to WebP (and SVG, if you choose to allow SVG uploads), and it can downscale oversized images to a maximum size you choose.

Step 1: Install and configure the plugin

1. Install BinsOptimizer. Go to Plugins > Add New, search for "BinsOptimizer", then install and activate it.
2. Open the settings. Go to Settings > BinsOptimizer.
3. Check that auto-optimize on upload is on. This is what converts new uploads automatically.
4. Set the quality. Adjust the JPEG and PNG quality settings. Start with the defaults, then lower them gradually if you want smaller files.
5. Set a max dimension. Choose the largest width or height you ever need. Anything bigger is downscaled during upload.
6. Save your settings.

Step 2: Upload images as usual

Now upload images the way you always do: through the Media Library, by dragging files into the block editor, into galleries, or as a featured image. BinsOptimizer works with the block editor, the Classic Editor, and drag-and-drop uploads.

Each upload is converted to WebP before it reaches your server. In the block editor, a notice reports the savings for each optimized image, and the Image block’s settings sidebar shows the original and optimized size.

Step 3: Bulk optimize your existing library

Images you uploaded before installing the plugin aren’t converted automatically. Bulk Optimize handles them.

1. Run the WebP delivery check first. Under the Compression settings, find the Existing images section and press Run check. It confirms your server actually serves .webp files.
2. Choose what happens to originals. In the same section, keep the default "Keep a restorable copy" so you can undo later.
3. Pick an optimization scope. Convert the full-size image only, or the full-size image plus all thumbnail sizes. Including thumbnails means the sizes visitors actually load are optimized too.
4. Open Bulk Optimize. Set a batch size and start the run. You can pause, resume, or cancel, and already-optimized images can be skipped.
5. Keep the browser tab open. Conversion happens in your browser, so closing the tab stops the run.

You can also optimize a single image with the Optimize It button in the Media Library.

What happens to images already used in posts?

Converting a published image changes its URL. BinsOptimizer rewrites those URLs across your post content, page builder data (including Elementor), widgets, and theme options during the run, so pages already using the image keep working.

Check Your Results

Don’t just trust the numbers. Measure them.

1. Check the Media Library. BinsOptimizer shows original and optimized file sizes and the savings for each image.
2. Run PageSpeed Insights. Test a key page at PageSpeed Insights before and after a bulk run. Look at LCP and any image-related suggestions.
3. Inspect an image. Right-click an image on the front end, open it in a new tab, and confirm the file ends in .webp.
4. Clear your caches. If you use a caching plugin or CDN, purge it so visitors get the new files.

Keep Originals and Backups

Optimization should never be a one-way door you can’t walk back through.

• Keep restorable copies. With "Keep a restorable copy" selected, originals are stored in wp-content/uploads/biio-originals/, and the Bulk Optimize screen offers an Undo optimization option that restores them and points your content back at them.
• Know the trade-off. Choosing to delete originals saves disk space, but that run can't be undone.
• Back up your site first. Take a full backup of files and database before any bulk change, whatever plugin you use.

Common Pitfalls to Avoid

WebP files returning “403 Forbidden”

Some security plugins and host firewalls only allow a fixed list of file extensions in the uploads folder, and .webp is often missing. Optimized images then fail to load. Run the WebP delivery check before bulk optimizing. If it fails, add .webp to the allowed extensions in your security plugin or ask your host.

Setting quality too low

Aggressive compression can create blurry product photos and banding in gradients. Compare a few images side by side before applying low quality settings across your whole library.

Skipping thumbnails

Themes often display thumbnail sizes, not the full image. If you optimize full-size images only, visitors may still download the old, heavier thumbnails.

Forgetting the cache

A page cache or CDN may keep serving old image URLs until you purge it.

Image Optimization Best Practices

• Resize before you compress. A 4000-pixel image shown at 800 pixels wastes bandwidth no matter the format.
• Write descriptive alt text. It helps accessibility and image search. Format changes don't affect it.
• Use the right image for the job. Logos and icons often work best as SVG. Photos suit WebP.
• Re-test after big changes. New themes and plugins can change how images load.

For more ways to speed up a block-based site, explore our Gutenberg block editor guide and our lightweight Gutenberg plugins.

Frequently Asked Questions

Does BinsOptimizer need an API key?

No. All optimization happens in your browser, so there are no external services to connect and no API key to manage.

Can I convert images I uploaded before installing the plugin?

Yes. Use Bulk Optimize to convert your existing Media Library, or the Optimize It button on a single image. Keep the browser tab open while a bulk run is going.

Will converting to WebP break images already on my pages?

No. Converting a published image changes its URL, and BinsOptimizer rewrites those URLs in post content, page builder data, widgets, and theme options as part of the run.

Can I undo a bulk optimization?

Yes, if originals are set to “Keep a restorable copy”, which is the default. The Bulk Optimize screen then offers an Undo optimization option. If you chose to delete originals, the run can’t be undone.

Start Serving Faster Images

Smaller images are one of the easiest speed wins on any site. Set up automatic conversion once, bulk optimize your existing library, and check the results in PageSpeed Insights. That’s how you convert images to WebP in WordPress without changing how you or your clients upload.

Download BinsOptimizer free from WordPress.org and make your next upload lighter. Questions about setup? Get in touch.