How many and which values can/should be unitless in CSS

I know two

• margin {0 auto}
• line-开发者_StackOverflow中文版height: 1.5;

is there any other?

The currently selected answer is out-of-date, and also misses a few of the ones in the CSS2 spec linked. As I needed a more up-to-date answer, here's a brief summary of what I've found.

Note that this is a list of which properties can be unitless, but not always necessarily should be. Also note obviously that any property which can accept a 'length' value can therefore accept the unitless value of 0.

This lists all CSS3 properties that accept numeric values ([i]nteger or [f]loat):

• animation-iteration-count (i)
• border-image-slice (f)
• border-image-width (f)
• column-count (i)
• counter-increment (i)
• counter-reset (i)
• flex (i)
• flex-grow (i)
• flex-shrink (i)
• font-size-adjust (f)
• font-weight (i)
• line-height (f)
• nav-index (i)
• opacity (f)
• order (i)
• orphans (i)
• tab-size (i)
• widows (i)
• z-index (i)

In addition to this list, the CSS2 specification also exclusively includes:

• pitch-range (f)
• richness (f)
• speech-rate (f)
• stress (f)
• volume (f)

And besides these, there are technically a few obscure ones (related to SVGs):

• flood-opacity (f)
• mask-box-outset / mask-border-outset (f)
• mask-box-width / mask-border-width (f)
• shape-image-threshold (f)

And, FTW, this seems to be a good reference of all properties that ever existed.

I don't really have an answer for your question, but I just wanted to say that I don't think you should ever leave off the units unless you're specifying a value of 0. It's easier to read and there's no guesswork (for both the browser and someone else who may be reading your CSS).

EDIT: Pulled this from a forum. They are the CSS properties that accept integer values for CSS 2.1 specifications:

• z-index
• font-weight
• line-height
• counter-reset
• counter-increment
• volume
• stress
• pitch-range
• richness

Every numerical value other than 0 should have a unit.

margin:0; //Good
margin:15; //Bad.  Do you want px, em, %, etc?

I am pretty sure I have had instances where leaving the value type off lead to display problems in other browsers. This is because they default to different types.
0 is 0 in any type.
Where 5px (pixels) can be a lot different then 5em (Width of the Current Fonts capital letter M).
As a best practice I say always use them. It's only a few more bytes of bandwidth.