How to Add Ad Units in Google Ad Manager (GAM) for Beginners

If you’re just starting with Google Ad Manager, one of the first things you need to understand is Ad Units.

Ad Units are the spaces on your website where ads appear. Think of them as “containers” that tell Google Ad Manager exactly where an advertisement should be displayed — like the header, sidebar, in-article section, or footer.

Without properly created Ad Units, GAM cannot serve ads correctly.

This beginner-friendly guide walks you through the entire process step by step.

---

What Are Ad Units in Google Ad Manager?

An Ad Unit is a defined ad placement inside your website or app.

Examples include:

• Homepage banner
• Sidebar rectangle
• Sticky footer ad
• In-article ad
• Mobile anchor ad

Each Ad Unit has:

• A unique name
• A unique code
• Supported ad sizes
• Targeting settings

These are later connected to:

• Line items
• Orders
• AdSense or Ad Exchange demand
• Header bidding partners

---

Why Proper Ad Unit Setup Matters

A clean Ad Unit structure helps with:

• Better reporting
• Easier troubleshooting
• Improved targeting
• Higher CPM optimization
• Cleaner header bidding integration
• Better inventory organization

Poorly organized ad units can create confusion later when your site scales.

---

Before You Start

You need:

• A working Google Ad Manager account
• Access to your website code or CMS
• Basic understanding of where ads will appear on your site

---

Step-by-Step: How to Add Ad Units in GAM

Step 1: Login to Google Ad Manager

Go to:

Google Ad Manager

After logging in:

• Open the left sidebar
• Click Inventory
• Select Ad Units

---

Step 2: Click “New Ad Unit”

Inside the Ad Units page:

• Click the New Ad Unit button
• A setup page will appear

This is where you define your ad placement.

---

Step 3: Enter Ad Unit Details

Ad Unit Name

Use descriptive names.

Good examples:

• Homepage_Top_Leaderboard
• Article_InContent_1
• Sidebar_Rectangle
• Mobile_Sticky

Avoid random names like:

• Ad1
• BannerTest
• Unit123

---

Ad Unit Code

This is automatically generated but can usually be customized.

Keep it:

• Short
• Clean
• Consistent

Example:

homepage_top
article_mid_1
sidebar_300x250

---

Step 4: Select Ad Sizes

Choose the ad sizes allowed in this placement.

Common desktop sizes:

• 728×90
• 300×250
• 336×280
• 160×600

Common mobile sizes:

• 320×50
• 300×250
• 320×100

You can:

• Add multiple sizes
• Use responsive sizes
• Enable fluid/native formats

Example:

300x250, 336x280

---

Step 5: Configure Target Window

You’ll usually see:

• Top Frame
• SafeFrame
• Friendly iframe

For beginners, the default setting is generally fine.

---

Step 6: Save the Ad Unit

Click:

Save

Your new Ad Unit is now created.

---

How to Generate the GAM Ad Tag

After saving:

1. Select the Ad Unit
2. Click Generate Tags
3. Choose:
   • Google Publisher Tag (GPT)
   • Single Request Architecture (recommended)

GAM will generate JavaScript code.

Example:

<div id='div-gpt-ad-123456'></div>
<script>
googletag.display('div-gpt-ad-123456');
</script>

You’ll place this code on your website where you want ads to appear.

---

Recommended Ad Unit Naming Structure

As your site grows, organization becomes important.

A good format is:

Site_Section_Position_Size

Example:

Blog_Header_728x90
Article_Mid_300x250
Mobile_Footer_320x50

This makes reporting much easier later.

---

Best Practices for Beginners

1. Keep Naming Consistent

Consistency prevents confusion when managing hundreds of placements later.

---

2. Avoid Too Many Sizes

Too many ad sizes can:

• Slow auctions
• Reduce bid competition
• Cause layout shifts

Stick to high-performing standard sizes first.

---

3. Separate Desktop and Mobile

Desktop and mobile behavior are very different.

Create dedicated units like:

Desktop_Top
Mobile_Top

instead of mixing everything together.

---

4. Use Responsive Design Carefully

Responsive ads are useful, but incorrect implementation can break layouts.

Test thoroughly on:

• Desktop
• Tablet
• Mobile

---

5. Plan for Future Growth

Even if your site is small now, structure inventory properly from the start.

This becomes critical when adding:

Direct campaigns

Ad Exchange

Open Bidding

Header bidding