Image File Size Estimator
Drop image files and instantly audit every one — actual size, dimensions, KB per megapixel, estimated WebP and AVIF savings. Fully offline — your images never leave your browser.
Drop your images
Drop images or pick files
All processing happens in your browser using the File API — nothing is uploaded. Supports JPG, PNG, WebP, AVIF, GIF, SVG.
How to Shrink Image Weight Without Losing Quality
Four rules that cut page weight by 50–70% on most sites.
Pick the right format for the job
Photos: JPEG, WebP, or AVIF. Line art and screenshots: PNG or WebP. Animation: MP4/WebM, never GIF. Icons and logos: SVG. Wrong format often doubles the file size.
Serve modern formats with fallback
Use <picture> with AVIF → WebP → JPEG. Modern browsers get 40–50% smaller files; older browsers still see the page. No client-side detection required.
Resize before you compress
A 4000×3000 hero image on a 1200px slot wastes 90% of the bytes. Resize to the largest actual display dimension, then compress. Retina: 2× display dimensions, then cap at 2400px.
Use responsive srcset + sizes
Mobile users shouldn't download desktop hero images. Ship 3–4 size variants via srcset and let the browser pick. Biggest single win on most sites.
Image Size Targets by Role
What to aim for by where the image lives on the page.
Hero image
Target: under 300KB, ideal 150KB. Max dimension: 1920px (or 2400px for retina). Usually the LCP element — optimise first.
Content image
Target: under 150KB, ideal 80KB. Max dimension: 1200px. Should never be the page's bottleneck.
Thumbnail
Target: under 50KB, ideal 20KB. Max dimension: 400px. If you have dozens on one page, aggressive optimisation matters.
Logo / icon
SVG if possible (bytes < pixels). PNG-24 fallback. Never JPG for logos — edges go fuzzy.
Decorative shape
SVG or CSS. Never a JPG/PNG. If you have to use raster, it's a CSS background-image with lazy loading.
Product photo
Under 200KB per image. Multiple sizes via srcset for listing vs detail view. WebP with JPEG fallback.
Gallery / lightbox
2 sizes per image: ~50KB thumb, ~400KB full. Lazy-load the full version only when lightbox opens.
Total page budget
Under 1MB for mobile LCP <2.5s. Over 2MB and mobile Core Web Vitals start slipping in rural-connection scenarios.
Why Image Weight Matters
Images are usually 60–70% of a page's total bytes. The biggest Core Web Vitals win sits here.
Core Web Vitals
Format & quality
Delivery
Cost & impact
Image File Size FAQ
Are my images uploaded anywhere?
No. Everything runs in your browser using the File API. Files are read locally, decoded to measure dimensions, and immediately released. Nothing is sent to any server or stored.
What's a good target size for web images?
Hero images: under 300KB. Content images: under 150KB. Thumbnails: under 50KB. These targets balance quality and page speed for a fast-loading experience.
Should I convert to WebP or AVIF?
Yes — WebP saves ~30% over JPEG and is supported in all modern browsers. AVIF saves ~45% but has slightly less support. Serve AVIF with WebP fallback via <picture> for best results.
How accurate are the WebP/AVIF estimates?
These are statistical averages from real-world web images. Your actual savings vary by content complexity — photographs compress better than text-heavy screenshots. Re-encode to get exact sizes.
Want Site-Wide Image Optimisation, Automated?
Our Australian team sets up image CDN, AVIF/WebP pipelines, and responsive srcset generation across your CMS — no more manual resize, no more page-speed penalties.
- CDN + AVIF pipeline setup
- Responsive srcset automation
- No lock-in commitment
No long-term commitment. Cancel anytime. 100% satisfaction guaranteed.