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1Scan for outdated or missing drivers - takes under a minute2Clear out junk files and repair common Windows errors3Fix the driver behind crashes, sound loss and screen glitchesvh and vw size CSS values against the viewport’s height and width; vmin and vmax follow whichever viewport dimension is shorter or longer. For mobile layouts, the newer svh, lvh, and dvh units help you choose how an element responds to browser controls such as the address bar.
What do vh, vw, vmin, and vmax mean?
Viewport units are lengths calculated from the viewport rather than from an element’s parent. That differs from a percentage such as width: 50%, which is generally resolved against the containing block. The W3C defines viewport-percentage lengths in its CSS Values and Units Level 4 specification; MDN summarizes the basic formulas in its viewport-relative length reference.
vh: 1% of the viewport height. If that height is 800 CSS pixels,50vhis 400 CSS pixels.vw: 1% of the viewport width. If that width is 1,200 CSS pixels,25vwis 300 CSS pixels.vmin: 1% of the smaller viewport dimension. It follows the shorter axis, even when orientation changes.vmax: 1% of the larger viewport dimension. It follows the longer axis.
These formulas refer to CSS pixels, not a device’s physical pixel dimensions. In an iframe, the units use that iframe document’s viewport rather than automatically measuring the top-level browser window; see MDN’s viewport-unit reference.
When should you use each viewport unit?
Use vh for height-driven layouts
Use vh when a section’s size should relate to viewport height and the default large-viewport behavior is acceptable. For example, a hero can occupy a substantial part of the screen without requiring a fixed pixel height:
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.hero {
min-height: 60vh;
padding: clamp(1rem, 3vw, 3rem);
}clamp() keeps the padding between a minimum and maximum while allowing it to scale fluidly in between. The values are design choices, not universal recommendations.
Use vw for width-driven sizing
vw is useful for spacing, grids, or type that should respond to viewport width. Unbounded viewport-based typography can become too small on narrow screens or too large on wide ones, so use a clamp() range when readability needs limits. For body text and controls, keep a usable lower bound rather than letting viewport scaling dictate every size.
Use vmin when the shorter axis should control
vmin suits elements that must remain proportionate to the available space in both portrait and landscape, such as a square avatar or a compact shape:
.avatar {
width: 20vmin;
height: 20vmin;
}Use vmax when the longer axis should control
vmax follows the longer side of the viewport. It can suit broad background effects intended to grow with the screen’s largest dimension. Because the longer axis can be especially large in landscape, consider bounding the result with min(), max(), or clamp() if the effect should not expand without limit.
Why can 100vh be too tall on mobile?
Mobile browsers may expand or retract interface elements such as the address bar. The layout viewport and the visual viewport are not always the same: pinch zoom, a virtual keyboard, or browser UI changes can shrink the area currently visible without changing the layout viewport in the same way. As a result, a 100vh element may extend behind browser controls instead of matching the currently visible height. MDN explains this distinction in its Visual Viewport API guide.
CSS now provides small, large, and dynamic viewport-unit families to make the intended behavior explicit. MDN documents that the default vh and vw units currently correspond to lvh and lvw, respectively, in its viewport-unit reference.
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| Unit family | Reference behavior | Useful when | Trade-off |
|---|---|---|---|
svh / svw |
Small viewport, with browser UI expanded | Keeping content within the available space while browser controls are present | May leave unused space after browser UI retracts |
lvh / lvw |
Large viewport, with browser UI retracted | Stable sizing against the largest viewport | Content may sit beneath expanded browser UI |
dvh / dvw |
Dynamic viewport, changing as browser UI expands or retracts | Matching the current viewport when fitting the visible area matters more than stable sizing | May resize during scrolling |
vh / vw |
Currently map to the large viewport units in MDN’s documented browser behavior | Height- or width-based sizing when that large-viewport behavior is acceptable | Can share the large-unit overlap behavior on mobile |
The W3C specification describes the viewport-unit families, and MDN explains their practical trade-offs in its reference. Choose based on what should happen while browser controls are visible: use a small unit when avoiding overlap is the priority, or a dynamic unit when tracking the changing viewport is worth the possibility of resizing.
How to choose svh, lvh, or dvh
Use svh when a panel should fit the viewport with browser UI expanded and you would rather tolerate extra space after that UI retracts. Use lvh when sizing for the largest viewport is more important than avoiding overlap while browser UI is expanded. Use dvh when the element should follow the changing viewport, accepting that its size can change as the browser interface moves.
A progressive declaration lets browsers that support dynamic units use them while retaining a fallback:
.panel {
min-height: 100vh;
min-height: 100dvh;
}Browsers that understand both declarations apply the later supported value; browsers without support for dvh retain the earlier 100vh rule. If avoiding browser-UI overlap is more important than dynamically filling the available space, use 100svh instead of the dynamic declaration where supported.
Set the viewport meta tag for mobile pages
Viewport units work with the browser’s viewport, so the page needs an appropriate mobile viewport configuration. MDN notes that without a viewport meta tag, some mobile browsers use a fixed initial containing-block width, typically 980 pixels. That can make a responsive layout behave as if its viewport were much wider than the device. Include this in the document’s <head>:
<meta name="viewport" content="width=device-width, initial-scale=1">See MDN’s viewport meta tag guide and explanation of viewport width and screen width.
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Make viewport-based layouts more robust
Viewport-relative sizing is a tool, not a guarantee that content will fit every screen or interaction state. For text and spacing that need limits, combine a viewport unit with rem-based bounds. Then check the states likely to change the available space:
- Long content that must scroll rather than be clipped.
- Zoomed pages and orientation changes.
- Virtual keyboards and expanded or retracted browser controls.
- Text, buttons, and focus targets that must remain readable and usable.
For a full-screen panel, choose the unit according to the browser-UI behavior you want, and avoid treating a single viewport height as a substitute for testing how the page behaves when the visible area changes.
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