MPU (Mid-Page Unit) Definition:

An MPU (Mid-Page Unit) is a rectangular display advertising format integrated into a web page, commonly within editorial content or in a side column. Its classic size is 300 x 250 pixels, also called a medium rectangle or inline rectangle.

The term describes an advertising unit rather than a behavior. An MPU does not necessarily cover the page, follow scrolling, or interrupt reading. It is one specific format within display advertising, not a separate advertising channel.

Table of contents

1 How an MPU works
2 Related sizes and names
3 Placement and adaptation across screens
4 Creative formats and loading experience
5 Measurement and differences from other formats

How an MPU works

The format combines a space reserved by the publisher with a creative supplied directly or through an advertising platform. The usual sequence includes:

Slot definition: the publisher establishes the position, dimensions, and technical conditions of the advertising space.
Ad request: when the page loads, the site or its advertising system requests a compatible creative.
Selection: the system chooses a campaign according to availability, bidding, context, and targeting criteria.
Rendering: the creative appears inside the reserved container; its file dimensions do not have to match the physical dimensions of the screen.
Recording: the platform counts delivery and interactions according to its measurement rules.

An MPU can be sold directly between an advertiser and publisher or form part of programmatic inventory. The buying mechanism does not change the nature of the format.

Related sizes and names

Google Ad Manager’s supported ad sizes distinguish several rectangular and square units:

300 x 250: the classic MPU, called a medium rectangle in Ad Manager and an inline rectangle in Google Ads uploaded-ad specifications.
336 x 280: known as a large rectangle. It has a similar proportion but is a separate size.
250 x 250: a related square format, not another universal name for a 300 x 250 MPU.
300 x 300: available in some media plans and inventories, although it is not a universal MPU specification.
300 x 600: known as a half-page ad. It has the same width as the classic unit but is considerably taller.

Fixed sizes remain in use, but they are not the only way to define inventory. The IAB guidelines also include flexible units based on aspect ratios and size ranges for delivery across different screens.

Placement and adaptation across screens

Placement forms part of the publisher’s implementation and is not determined by dimensions alone:

In-content: inserted between paragraphs, modules, or editorial blocks.
Side column: placed next to the main content in layouts with sufficient width.
End of article: displayed after the editorial body or before other navigation modules.
Responsive container: retains an aspect ratio or changes size when the layout and platform support flexible inventory.

A fixed 300-pixel-wide ad can fit many mobile screens, but that does not guarantee responsive integration. The container, margins, and loading behavior also need to adapt. If the unit remains visible while the page scrolls, expands, or overlays content, those are behavioral properties rather than part of the basic definition of an MPU.

Creative formats and loading experience

The same slot can contain creatives with different levels of complexity:

Static image: combines imagery, text, and a call to action in a graphic file.
Animation: uses a limited sequence or motion to present several elements.
HTML5: can add transitions and interaction within the platform’s restrictions.
Responsive creative: rearranges its elements to fit more than one compatible size.
Dynamic content: changes products, messages, or other components using a catalogue or campaign rules.

Technical capability does not guarantee a better experience or higher performance. File weight, loading time, visual stability, legibility, contrast, and animation controls all affect the result. An MPU does not need to be intrusive either: it can remain within its allocated space without hiding or unexpectedly moving the content.

Measurement and differences from other formats

Performance is assessed using display-advertising metrics:

Impressions: the number of times the platform records delivery of the ad.
Viewable impressions: deliveries that meet the visibility criterion used by the measurement system.
Clicks and CTR: interactions and the proportion of clicks relative to counted impressions.
Conversions: actions attributed after an interaction or, where the model includes them, after a view.
Frequency: the average number of ad exposures per measurable user or identifier.

These metrics depend on the campaign and its methodology. A prominent placement can increase the opportunity to view an ad, but it does not guarantee attention, clicks, or conversions.

An MPU differs from nearby concepts:

Banner: a general category covering different graphic units and sizes; an MPU is one of those formats.
Display advertising: the broader system for distributing and buying visual ads across websites and applications.
Half-page ad: a vertical 300 x 600 unit, larger than the classic MPU.
Interstitial: an ad that occupies the full screen or appears between two content states.
Native advertising: adapts its presentation to the editorial environment, whereas an MPU usually retains an identifiable advertising container.