Large, unoptimized images can increase page weight and slow down loading, especially for visitors on mobile networks. This guide explains practical ways to choose suitable formats, reduce file size, resize images correctly, write helpful alt text, and check the results before publishing.
Why Image Optimization Matters
Images are often among the largest files downloaded on a webpage, particularly on pages with photographs, banners, product images, or galleries. When someone visits a site on a phone with a limited connection, large images can be the main reason the page takes longer to appear.
Page experience and loading performance can affect how easily visitors use a site. Optimized images can also support better performance metrics and improve the likelihood that visitors stay engaged.
Smaller image files can reduce the amount of data transferred when visitors load a page, which may also reduce bandwidth use depending on your hosting setup.
Step 1: Pick the Right Format
The format you choose affects both file size and image quality. Here is a comparison of common web image formats:
| Format | Best For | Compression | Relative Size | Transparency |
|---|---|---|---|---|
| JPEG | Photos, complex images | Lossy | Usually small | No |
| PNG | Logos, screenshots, graphics | Lossless | Usually larger | Yes |
| WebP | Photos, graphics, transparency | Lossy or lossless | Often smaller than JPEG or PNG in comparable cases | Yes |
File size and visual quality depend on the image, encoder settings, dimensions, and compression level. Test important images rather than assuming one format will always produce the smallest file.
WebP is a practical choice for many websites because it supports both lossy and lossless compression, transparency, and broad modern-browser support. Chrome, Firefox, Edge, and Safari all support it.
AVIF can produce smaller files for some images, but the best choice depends on your CMS, workflow, audience, and fallback support. WebP remains a practical option for many websites because it is widely supported and works well for both photos and graphics.
Step 2: Compress Before Uploading
A photo straight from a camera or phone can be several megabytes. After compression at web-appropriate settings, the same image may be a few hundred kilobytes — and the difference is often hard to notice on screen.
The Image Compressor is designed to process supported files in your browser. Review the tool page for current format support, file-size limits, browser requirements, and privacy details before use.
You can also compare results with desktop or browser-based image optimization software. Review each tool's supported formats, privacy approach, and operating-system compatibility before using it.
Quality Settings to Consider
For blog images, around 80% quality is a common starting point. For product photos where detail matters, 85–90% may be appropriate. For thumbnails and background images, lower settings often work well. Compare the original and compressed version before saving.
Step 3: Resize to the Dimensions You Need
Uploading a 4000-pixel-wide photo when your website displays it at 800 pixels means the browser downloads far more data than necessary. Match your image dimensions to what the layout actually uses.
Most blogs display featured images at around 1200 pixels wide. Product images might be 800 pixels square. Check your site's layout and resize accordingly. The Image Resizer can help with this — set the width and height you need, and it processes the image in your browser.
Step 4: Use Descriptive Filenames and Alt Text
Search engines cannot interpret images visually. They rely on filenames and alt text to understand what an image contains. A filename like IMG_4578.jpg provides no useful information. A name like red-running-shoes-forest-trail.jpg gives context.
Write concise alt text that describes the purpose or important content of the image. Use keywords only when they naturally describe the image, and avoid repeating nearby text or adding keywords that are not relevant. Alt text also helps people who use screen readers understand what is on the page.
Step 5: Add Lazy Loading
Lazy loading defers images until the visitor scrolls near them. Images near the top of the page load as usual; images further down wait. This reduces the initial data the browser must download.
Adding it requires one attribute:
<img src="image.jpg" loading="lazy" alt="description">
Do not lazy-load the image that is likely to be the main visible image near the top of the page. Loading that image normally can help avoid delaying the page's largest visible content.
Step 6: Use Responsive Images
Different screen sizes need different image dimensions. A phone does not need the same large file as a desktop monitor. Responsive images let the browser choose the most appropriate size:
<img
src="image-800w.jpg"
srcset="image-400w.jpg 400w,
image-800w.jpg 800w,
image-1200w.jpg 1200w"
sizes="(max-width: 600px) 400px,
(max-width: 900px) 800px,
1200px"
width="1200"
height="800"
alt="Description of image">
Set width and height attributes, or reserve space with CSS, so images do not cause layout shifts while loading. The values should match the actual aspect ratio of each image.
Step 7: Check Your Results
Use Google PageSpeed Insights to review a page after making changes. Its recommendations can help identify oversized images, inefficient image delivery, layout shifts, and other performance opportunities. Test more than once and compare results with real visitor data when it becomes available.
Start Optimizing Your Images
Compress supported image files in your browser and compare the result before downloading. File-size savings vary by image type, dimensions, format, and selected quality.
Open Image CompressorCommon Questions About Image Optimization
What is the best image format for websites?
WebP is a practical choice for many websites because it supports both lossy and lossless compression, transparency, and broad modern-browser support. AVIF may create smaller files in some cases, so test both formats when your workflow supports them.
How much can I compress an image before it looks bad?
It depends on the image. Photographs can often handle moderate compression without a visible difference. Graphics and logos with text may need higher quality settings. The best approach is to adjust quality gradually and compare the result before saving. The Image Compressor shows a preview so you can compare before downloading.
Does image optimization help SEO?
Image optimization can support SEO indirectly by improving loading performance and user experience. Descriptive filenames, appropriate alt text, relevant surrounding content, and accessible image delivery can also help search engines understand image context. Rankings depend on many factors, so image optimization alone does not guarantee traffic.
What size should my images be for a blog?
For social sharing, 1200 × 630 pixels is a commonly used Open Graph image size. For images inside an article, choose dimensions based on the maximum display width in your layout, then compress and test the result.
Should I use a CDN for images?
A CDN can help deliver static files efficiently to visitors in different locations, but it does not replace resizing, compression, responsive images, and proper caching. Choose a CDN only if it fits your site's traffic, budget, and technical setup.