Understanding Prebid Mobile Price Granularity: A Practical Guide for Publishers

If you’re running header bidding on mobile and want to optimize every cent of programmatic revenue, understanding how Prebid Mobile handles bid values is critical. Publishers often discover too late that their price granularity setup directly impacts both auction accuracy and operational complexity.

This guide explains how price granularity works in Prebid Mobile, why it matters for your ad server setup, and what every publisher should keep in mind to maximize control and results without drowning in admin work.

What Is Price Granularity in Prebid Mobile?

Price granularity determines how finely you distinguish between different bid prices when passing them from Prebid Server to your ad server. Instead of tracking every possible CPM down to the penny, granularity allows you to group bid values into “buckets” that dictate how many line items you’ll need and how precise your price targeting can be.

Why Does Granularity Matter?

Using too many price points (very fine granularity) leads to a massive number of ad server line items, increasing management overhead and error risk. Too few price points (coarse granularity) means leaving money on the table, as high bids get grouped down with lower ones, reducing the true value of your inventory.

How Prebid Mobile Handles Price Buckets

Prebid Mobile relies on the ad server key-value pair ‘hb_pb’ to pass the bucketed bid value. When a demand partner bids, Prebid Server assigns the bid to a price bucket based on your configured granularity, then sends this to your ad server via the SDK or API. Your ad server matches this with a corresponding line item priced for that bucket.

Real-World Example: Setting Up Line Items in GAM

Suppose you set a granularity of $0.10. If you receive a bid of $1.07, it is rounded down to $1.00 or $1.10 (depending on your rules). You must then have a line item in GAM matching that bucket. With penny increments ($0.01), you’d need hundreds or thousands of line items—impractical for most teams.

Granularity Options: Tradeoffs and Implementation

Prebid Mobile and Prebid Server offer five main granularity presets—each with different implications for precision and management:

– Low: Buckets bids in $0.50 increments, up to $5 CPM. Fewer line items, less precision.
– Medium: Buckets bids in $0.10 increments, up to $20 CPM. A balance of manageability and accuracy.
– High: Buckets bids in $0.01 increments, up to $20 CPM. Maximum granularity, but labor-intensive if done manually.
– Auto: Uses a sliding scale, finer at lower CPMs, coarser at higher CPMs.
– Dense: Like Auto, but even more granular at low CPMs.
– Custom: Define your own breakpoints for unique strategies.

Different media types (e.g., banner vs. video) can have different granularities—helpful when price variation or inventory value differs drastically by format.

Auto and Dense Granularity in Practice

For example, ‘Auto’ will round all sub-$5 CPM bids to the nearest $0.05, while high CPMs get bucketed more coarsely. ‘Dense’ is even more precise under $3 CPM, which can be useful for inventory that regularly attracts lower-value bids but requires maximized auction competitiveness.

Practical Pitfalls and How to Avoid Them

Many publishers overcomplicate their setup by choosing extremely fine granularity without the operational bandwidth to manage thousands of line items. Others go too coarse, oversimplifying and missing out on higher CPMs. Another common mistake: not aligning price buckets between Prebid Server and the ad server, causing misfires and lost revenue.

Best Practices for Publishers

– Start with ‘med’ or ‘auto’ granularity for balance
– Audit your line item setup regularly for coverage gaps and bloat
– Coordinate closely between ad ops and development when changing granularity settings
– Test custom buckets if you have unique inventory or large volume at specific price points
– Use separate granularities for video if it commands much higher CPMs than display

What this means for publishers

Choosing and maintaining the right price granularity directly impacts operational workload and revenue outcomes. Proper setup means manageable line item numbers, precise auction matching, and minimized discrepancies between what buyers bid and what you earn. Failing to align granularity between your Prebid stack and ad server will almost always lead to inefficiency, lower yields, or accidental losses in the workflow.

Practical takeaway

To maximize value, start with a sensible preset like ‘med’ or ‘auto’ unless you have clear data suggesting otherwise. Regularly review the performance and complexity of your current granularity; don’t be afraid to adjust if your team’s workload spikes or revenue opportunity changes. Above all, keep communication tight between ad ops and your technical teams—granularity decisions touch both the daily workflow and the bottom line.

If you’re planning major changes or considering a custom setup, leverage test environments and monitor for mismatches before rolling out widely. A thoughtful, data-driven approach to price buckets not only simplifies operations but also ensures you capture the full value of your mobile audiences.