Minimum and maximum value of z-index?

http://www.w3.org/TR/CSS21/visuren.html#z-index

'z-index' Value: auto | | inherit

http://www.w3.org/TR/CSS21/syndata.html#numbers

Some value types may have integer values (denoted by ) or real number values (denoted by ). Real numbers and integers are specified in decimal notation only. An consists of one or more digits "0" to "9". A can either be an , or it can be zero or more digits followed by a dot (.) followed by one or more digits. Both integers and real numbers may be preceded by a "-" or "+" to indicate the sign. -0 is equivalent to 0 and is not a negative number. Note that many properties that allow an integer or real number as a value actually restrict the value to some range, often to a non-negative value.

So basically there are no limitations for z-index value in the CSS standard, but I guess most browsers limit it to signed 32-bit values (−2147483648 to +2147483647) in practice (64 would be a little off the top, and it doesn't make sense to use anything less than 32 bits these days)

My tests show that z-index: 2147483647 is the maximum value, tested on FF 3.0.1 for OS X. I discovered a integer overflow bug: if you type z-index: 2147483648 (which is 2147483647 + 1) the element just goes behind all other elements. At least the browser doesn't crash.

And the lesson to learn is that you should beware of entering too large values for the z-index property because they wrap around.

Out of experience, I think the correct maximum z-index is 2147483647.

It's the maximum value of a 32 bits integer: 2147483647

Also see the docs: https://www.w3.org/TR/CSS22/visuren.html#z-index (Negative numbers are allowed)

It depends on the browser (although the latest version of all browsers should max out at 2147483638), as does the browser's reaction when the maximum is exceeded.

Z-Index only works for elements that have position: relative; or position: absolute; applied to them. If that's not the problem we'll need to see an example page to be more helpful.

EDIT: The good doctor has already put the fullest explanation but the quick version is that the minimum is 0 because it can't be a negative number and the maximum - well, you'll never really need to go above 10 for most designs.

Conclusion Maximum z-index value is 2,147,483,647 and more than this convert to 2,147,483,647

‌Browser Maximum More Than Maximum Chrome >= 29 2,147,483,647 2,147,483,647 Opera >= 9 2,147,483,647 2,147,483,647 IE >= 6 2,147,483,647 2,147,483,647 Safari >= 4 2,147,483,647 2,147,483,647 Safari = 3 16,777,271 16,777,271 Firefox >= 4 2,147,483,647 2,147,483,647 Firefox = 3 2,147,483,647 0 Firefox = 2 2,147,483,647 Bug: tag hidden

All Values tested in BrowserStack.

I have found that often if z-index isn't working its because its parent/siblings don't have a specified z-index.

So if you have:

<div id="1">
    <a id="2" style="z-index:2"></a>
    <div id="3" style="z-index:1"></div>
    <button id="4"></button>
</div>

item #3, or even #4, may be contesting #2 for the click/hover space, though if you set #1 to z-index 0, the siblings who's z-index put them in independant stacks now are in the same stack and will z-index properly.

This has a helpful and fairly humanized description: http://foohack.com/2007/10/top-5-css-mistakes/  

A user above says "well, you'll never really need to go above 10 for most designs."

Depending on your project, you may only need z-indexes 0-1, or z-indexes 0-10000. You'll often need to play in the higher digits...especially if you are working with lightbox viewers (9999 seems to be the standard and if you want to top their z-index, you'll need to exceed that!)

There exist super easy way to write maximal and minimal value for z-index using calc().

Maximal value:

#some-id {
  z-index: calc(9e999)
}

Minimal value:

#some-id {
  z-index: calc(-9e999)
}

calc() Browser compatibility ( value support)

Firefox - 48+

Safari - 7+

IE - 9+

Opera - 18+

Chrome - 31+

Edge - 12+

While INT_MAX is probably the safest bet, WebKit apparently uses doubles internally and thus allows very large numbers (to a certain precision). LLONG_MAX e.g. works fine (at least in 64-Bit Chromium and WebkitGTK), but will be rounded to 9223372036854776000.

(Although you should consider carefully whether you really, really need this many z indices…).