What Is the Highest z-index in CSS?

When dealing with overlapping elements in CSS, the z-index property plays a crucial role in controlling which elements appear on top. But a common question among developers is:

“What is the highest z-index value I can use in CSS?”

Let’s answer that — and clear up a few myths along the way.

Table of Contents

✅ Quick Answer

There is no official “maximum” z-index value defined by the CSS specification.
However, practical limits are imposed by browser engines and integer size restrictions in JavaScript and rendering systems.

📈 Theoretical Maximums

Most modern browsers support very large integers as z-index values:

Browser Engine	Practical Max Value
Chrome (Blink)	~2,147,483,647 (2³¹−1)
Firefox (Gecko)	~2,147,483,647
Safari (WebKit)	~2,147,483,647

So yes — technically, you could do:

.super-element {
  position: absolute;
  z-index: 2147483647;
}

🔒 But that doesn’t mean you should.

⚠️ Why You Should Avoid Extreme `z-index` Values

While setting z-index: 99999 or more might seem like an easy fix, it’s not a scalable solution. Here’s why:

❌ Maintenance Nightmare

If everyone uses high z-indexes without structure, your layout quickly becomes unmanageable.
Debugging conflicts between z-index: 100000 and z-index: 999999 becomes a guessing game.

❌ Can Create Unexpected Bugs

Browsers may round or clamp large values inconsistently.
Stacking context and nested elements may override even a high z-index.

🧠 Best Practice: Use a Layering Scale

Instead of randomly increasing values, create a clear z-index scale in your design system or utility framework.

Example:

Layer	z-index
Base content	0
Dropdown	10
Sticky header	100
Modal	1000
Tooltip	1100+

This keeps things predictable and avoids “z-index wars.”

✅ Summary

Question	Answer
Max usable z-index?	Up to ~2,147,483,647 (2³¹−1)
CSS spec limit?	None — uses integers
Should you go that high?	No — use a consistent scale
Best practice?	Organize with a layer system

🚀 Final Thoughts

Yes, you can set a z-index of over 2 billion. But that’s like using a bazooka to hang a picture frame. Use a consistent z-index scale and manage stacking contexts thoughtfully. Your team — and your future self — will thank you.