What is Web Preview?
This tool simulates how an image will be displayed on a website. Photos taken with a digital camera or smartphone are often very large at their native pixel size. With this tool, you can preview how the image will look when scaled up or down to any display size. It is ideal for visualizing the result before changing CSS width/height values, or for getting a feel for sizes when designing banners.
Practical limitations
The preview here is a CSS-style resize and does not actually resample pixel data (bilinear, Lanczos, etc.). As a result, scaled-down rendering depends on the browser's rendering engine and may differ slightly from the result of a true image resizing tool. On Retina (2x/3x) displays, the gap between physical pixels and logical CSS pixels means the appearance differs from a standard display.
Drawbacks and trade-offs
You can only check the display size of a single image; the actual layout context of a webpage (text wrapping, responsive behavior, lazy-load effects, etc.) is not reproduced. For true responsive checking use our Responsive Preview tool, and for actual resampling use the Image Resize tool. Some SVG and animated GIF previews may not render perfectly accurately either.
On-the-job Q&A
Q: I want to find the optimal size for the web. - Typical website content widths range from 800-1200px. Considering Retina displays, the best practice is to prepare images at 2x the display size. For instance, if you display at 600px wide, prepare a 1200px wide image. Q: What is a good banner image size? - Use this tool to preview Google Display Ads recommended sizes (300x250, 728x90, 160x600, etc.) and SNS header sizes at actual scale to simulate appearance in advance.
Trends in web image display
Responsive images are the standard for the 2020s web. Using HTML's srcset and sizes attributes, the optimal image is auto-selected for the screen width and device pixel ratio. Server-side optimization with the Content-DPR HTTP header and lazy loading via the Intersection Observer API are also widespread. Choosing the right image size is one of the most effective tactics for improving LCP (Largest Contentful Paint) in Core Web Vitals.