Ad inventory is the total advertising space a publisher can sell across an app or website. It is the raw material of ad monetization: every banner slot, interstitial break, rewarded moment, and offerwall entry point is a unit of inventory that can either sit empty or earn. How much you have matters, but how well each unit performs matters more.

What counts as inventory

Inventory is measured in the ad placements a publisher can sell: banners, interstitials, rewarded video, native units, and offerwall placements. Its value depends on how much of it actually fills with paying demand (fill rate) and how much each placement earns (eCPM).

Two numbers turn inventory into revenue. Fill rate is the share of ad requests that get filled with a paying ad. eCPM is what each thousand filled impressions earns. A large amount of inventory with poor fill and low eCPM can earn less than a small amount of premium inventory that fills reliably.

Not all inventory is equal. Premium placements in high-attention moments command strong demand, while remnant slots that advertisers pass over sell for little. Part of a publisher's job is knowing which of their inventory is premium and pricing or routing it accordingly, rather than treating every slot as interchangeable.

Types of ad inventory

• Display units such as banners and native ads that run continuously in the background of the experience.

• Full-screen units such as interstitials and rewarded video that take over the screen at natural breaks.

• Engagement units such as the offerwall, where users opt in and complete offers for a reward.

Ad inventory vs. impressions

Inventory is the space you have to sell. An ad impression is a single instance of that space being filled and shown. You can hold a lot of inventory and still generate few impressions if fill rate is low or traffic is thin. Inventory is the supply; impressions are what you actually deliver against it.

How publishers make inventory more valuable

• Add higher-value placements rather than simply adding more low-value ones.

• Improve targeting and relevance so demand competes harder for each impression.

• Introduce engagement-based formats that users opt into.

The offerwall as premium inventory

An offerwall is one of the highest-value units a publisher can add, because it monetizes intent rather than attention. A single completed offer can earn more than thousands of passive banner views, and it reaches users who would never make an in-app purchase. RevU helps publishers turn one offerwall placement into an incremental revenue stream that sits on top of existing ads and purchases, matching offers to users so more of the placement converts.

Common mistakes to avoid

• Adding volume for its own sake. More low-value slots can crowd the experience and push users away without moving revenue much.

• Judging inventory by impressions alone. A placement is only worth what it earns after fill and eCPM are accounted for.

• Ignoring the user. Overloaded inventory raises short-term impressions and long-term churn at the same time.