box-sizing
Sets how the total width and height of an element is calculated. border-box includes padding and border in the size, while content-box does not.
Quick example
* {
box-sizing: border-box;
/* best practice: include padding/border in width/height */
}Quick facts
Initial value
content-boxInherited
No
Applies to
all elements that accept width or height
Animation type
discrete
Values
content-boxborder-box box-sizing Browser Support
Widely available Since 2015 96% global usage
This feature is well established and works across many devices and browser versions. It has been available across browsers since 2015.
Safe to use without fallbacks.
10+
29+
5.1+
12+