Best Image Size for Web
Web images should be large enough to look sharp on retina displays but small enough to load quickly.
Dimensions
Hero images: 1920×1080 or 1600×900. Blog images: 1200px wide. Thumbnails: 400–600px. Match your layout; don't serve 4000px images for a 800px container.
File Size
Keep images under 200KB when possible. Use compression and appropriate formats. Lazy loading helps for long pages.
Tools
Resize with super resolution if upscaling, or resize down for thumbnails. Compress before upload. Use format conversion (WEBP) where supported.