March 1Mar 1 Administrators CSS Units CSS Units CSS has several different units for expressing a length. Many CSS properties take "length" values, such as width, margin, padding, font-size, etc. Length is a number followed by a length unit, such as 10px, 2em, etc. Example Set different length values, using px (pixels): h1 { font-size: 60px;}p { font-size: 25px; line-height: 50px;} Try it Yourself » Note: A whitespace cannot appear between the number and the unit. However, if the value is 0, the unit can be omitted. For some CSS properties, negative lengths are allowed. There are two types of length units: absolute and relative. Absolute Lengths The absolute length units are fixed and a length expressed in any of these will appear as exactly that size. Absolute length units are not recommended for use on screen, because screen sizes vary so much. However, they can be used if the output medium is known, such as for print layout. Unit Description cm centimeters Try it mm millimeters Try it in inches (1in = 96px = 2.54cm) Try it px * pixels (1px = 1/96th of 1in) Try it pt points (1pt = 1/72 of 1in) Try it pc picas (1pc = 12 pt) Try it * Pixels (px) are relative to the viewing device. For low-dpi devices, 1px is one device pixel (dot) of the display. For printers and high resolution screens 1px implies multiple device pixels. Relative Lengths Relative length units specify a length relative to another length property. Relative length units scale better between different rendering medium. Unit Description em Relative to the font-size of the element (2em means 2 times the size of the current font) Try it ex Relative to the x-height of the current font (rarely used) Try it ch Relative to the width of the "0" (zero) Try it rem Relative to font-size of the root element Try it vw Relative to 1% of the width of the viewport* Try it vh Relative to 1% of the height of the viewport* Try it vmin Relative to 1% of viewport's* smaller dimension Try it vmax Relative to 1% of viewport's* larger dimension Try it % Relative to the parent element Try it Tip: The em and rem units are practical in creating perfectly scalable layout!* Viewport = the browser window size. If the viewport is 50cm wide, 1vw = 0.5cm. Browser Support The numbers in the table specify the first browser version that fully supports the length unit. Length Unit em, ex, %, px, cm, mm, in, pt, pc 1.0 3.0 1.0 1.0 3.5 ch 27.0 9.0 1.0 7.0 20.0 rem 4.0 9.0 3.6 4.1 11.6 vh, vw 20.0 9.0 19.0 6.0 20.0 vmin 20.0 12.0 19.0 6.0 20.0 vmax 26.0 16.0 19.0 7.0 20.0 ★ +1 Sign in to track progress
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