Measurement

eCPM, ARPDAU, Fill Rate: What Each Metric Can and Cannot Tell You

A practical metrics guide for app teams who need to diagnose revenue changes.

By Maya Chen · Updated June 2026 · Educational guide
Custom diagram for eCPM, ARPDAU, Fill Rate: What Each Metric Can and Cannot Tell You

This article is written for app publishers and ad operations teams. It is not a vendor pitch and does not require a specific mediation platform, exchange, SDK, or DSP.

What the metric really means

A practical metrics guide for app teams who need to diagnose revenue changes. In day-to-day ad operations, the useful question is not whether a tactic sounds advanced. The useful question is whether it can be observed, tested, and explained when revenue changes. This guide focuses on signals a small app team can actually inspect.

For new inventory, avoid making several changes at once. Keep one clean baseline, record the date of each experiment, and compare results by country, format, operating system, and app version. A small change can look successful overall while damaging a valuable segment.

How to read the report

A practical metrics guide for app teams who need to diagnose revenue changes. In day-to-day ad operations, the useful question is not whether a tactic sounds advanced. The useful question is whether it can be observed, tested, and explained when revenue changes. This guide focuses on signals a small app team can actually inspect.

For new inventory, avoid making several changes at once. Keep one clean baseline, record the date of each experiment, and compare results by country, format, operating system, and app version. A small change can look successful overall while damaging a valuable segment.

SignalWhy it mattersWhat to check
eCPMUsually changes bid density or user tolerance.Compare before/after by format and country.
ARPDAUHelps explain whether the issue is demand, inventory, or policy.Inspect logs, dashboard filters, and partner notes.
fill rateOften becomes the hidden cause of revenue swings.Track it in the weekly review, not only during emergencies.

Diagnosis workflow

A practical metrics guide for app teams who need to diagnose revenue changes. In day-to-day ad operations, the useful question is not whether a tactic sounds advanced. The useful question is whether it can be observed, tested, and explained when revenue changes. This guide focuses on signals a small app team can actually inspect.

For new inventory, avoid making several changes at once. Keep one clean baseline, record the date of each experiment, and compare results by country, format, operating system, and app version. A small change can look successful overall while damaging a valuable segment.

What not to overreact to

A practical metrics guide for app teams who need to diagnose revenue changes. In day-to-day ad operations, the useful question is not whether a tactic sounds advanced. The useful question is whether it can be observed, tested, and explained when revenue changes. This guide focuses on signals a small app team can actually inspect.

For new inventory, avoid making several changes at once. Keep one clean baseline, record the date of each experiment, and compare results by country, format, operating system, and app version. A small change can look successful overall while damaging a valuable segment.

Practical checklist

A practical metrics guide for app teams who need to diagnose revenue changes. In day-to-day ad operations, the useful question is not whether a tactic sounds advanced. The useful question is whether it can be observed, tested, and explained when revenue changes. This guide focuses on signals a small app team can actually inspect.

For new inventory, avoid making several changes at once. Keep one clean baseline, record the date of each experiment, and compare results by country, format, operating system, and app version. A small change can look successful overall while damaging a valuable segment.

Example operating note

A useful internal note is short: what changed, where it changed, when it started, which segments moved, and what action will be reversed if the test fails. This habit makes monetization experiments easier to trust.

MC
Maya Chen

Former ad operations lead focused on app inventory, ad quality, and publisher revenue operations.