Measure any image on a site that already exists
If you are about to replace an image you need the exact size to export it at; Cota shows you without installing anything.
Measure with one click
Measure with Cota- Drag this button to your bookmarks bar.
- Open the site you want to measure and click the bookmark.
- Hover any image: Cota marks the size to export it at, the file’s real size, and whether it is right, too big or too small. Click to pin the result.
Some heavily protected sites block bookmarklets; if it doesn’t work, use the calculator below. Don’t see your bookmarks bar? Ctrl/Cmd+Shift+B shows it. On your phone? There’s no bookmarks bar there: use the calculator below.
Prefer to do it by hand, or on your phone?
Work it out by hand
Most screens today are high-density: use 2. Older screens or projectors: use 1.
Export your image at 960px wide.
rendered width × screen density (DPR)
Measuring it with the browser tools
On a computer, this takes about 2 minutes
Put the cursor over the image you want to measure and right-click.
In the menu, choose "Inspect" (or "Inspect element").
In the panel that opens, hover the <img> tag: the browser shows the size it renders at on screen (rendered size).
Multiply that number by 2 (most screens today are high-density). That is the width to export at.
To know how much space your image takes on that site (not the weight of the file you download), use the browser tools: it is the only reliable number.
In technical terms: what you want is the rendered size (how much it takes on screen), not the intrinsic size (the downloaded file).