What a placeholder image is for
A placeholder stands in for a picture that doesn’t exist yet: the hero photo still being shot, the product images a client hasn’t sent, the ad a campaign will fill later. It’s the right size, so the layout around it behaves exactly as it will with the real picture, and it says its size on it, so anyone looking at the mockup knows what has to go there. Designers drop them into wireframes, developers into templates and tests, and writers into drafts.
Choosing the size
Type the size the real image will be shown at. The ready-made list covers the common ones: screens (HD 1280 × 720, Full HD 1920 × 1080, 4K), social posts (an Instagram post is 1080 × 1080, a link preview 1200 × 630, a YouTube thumbnail 1280 × 720) and the standard ad sizes, like the 300 × 250 medium rectangle and the 728 × 90 leaderboard. The swap button turns a landscape size into a portrait one, and Keep the shape changes the height with the width, so a 16:9 image stays 16:9.
Which format to download
PNG is the safe choice: sharp text, and it can be transparent. JPG suits a placeholder for a photo, where a page or a tool expects one, but it can’t be transparent. WebP is smaller than both and works in every current browser. GIF is for old systems and email tools that want one. SVG is drawing instructions instead of pixels, so it’s tiny and stays sharp at any size, and is the best choice for a web page you control.
Sharp on high-resolution screens
Phones and Retina screens use two or three real pixels for every pixel a web page asks for. A 600 × 400 image shown at 600 × 400 on them is stretched and looks soft. Pick 2× and the file is drawn at 1200 × 800 instead: shown at 600 × 400, it’s sharp. Copy HTML writes the shown size into the tag for you.
Made in your browser
There’s no server behind this page. The preview, the files and the copied code are all made by your browser, so what you type isn’t sent anywhere, and nothing is stored apart from your format, font and sharpness, kept on this device so they’re ready next time.