CSS viewport 3840 × 2160 pixels at 1× device pixel ratio. The exact size browsers report on the 4K UHD.
The 4K UHD viewport is 3840 × 2160 CSS pixels, with a device pixel ratio of 1 on a 3840 × 2160 pixel display.
Test your site at 4K UHD (3840 × 2160)
When a user visits your site on the 4K UHD, the browser reports window.innerWidth = 3840 and window.devicePixelRatio = 1. Your CSS media queries match against the 3840px CSS width, not the 3840 × 2160 physical pixel count of the panel.
At 3840px it hits Tailwind 2xl (1536px) and Bootstrap xxl (1400px).
For sharp full-width images, serve a source at least 3840px wide (3840 CSS px × 1 DPR) through srcset and let the browser pick it.
/* 4K UHD: 3840×2160 CSS px, DPR 1 */
@media (max-width: 3840px) {
/* styles for this width and narrower */
}
@media (min-resolution: 1dppx) {
/* serve high-density assets */
}The 4K UHD reports a CSS viewport of 3840×2160 pixels. Browser toolbars reduce the visible height slightly, so window.innerHeight is usually smaller than the full screen height.
The 4K UHD uses a default device pixel ratio of 1. Each CSS pixel maps to 1×1 physical pixels on its 3840×2160 panel (at 100% scaling).
At 3840px wide it matches Tailwind 2xl (min-width 1536px) and Bootstrap xxl (min-width 1400px).
Open screensize.io, enter your URL and pick 4K UHD (3840×2160). It opens your site in a real browser window at exactly that CSS viewport, so media queries, container queries and JavaScript resize logic behave as they would on the device. For touch behaviour and the real browser engine, confirm on hardware before shipping.
See the full list of device viewport sizes →
Or browse common screen sizes by category →
Use screensize.io to preview your website at any of these resolutions instantly — no DevTools needed.
Open screensize.io →