Definition
WordPress plugin download volume is the count of times plugins were downloaded from WordPress.org in a given week. It includes downloads triggered when an existing install updates to a new version, not only fresh installs. Rivale sums this figure across a defined group of plugins. The number describes the group, not any one listing.
Population and window
Rivale measures download volume across the top 12,500 plugins, the plugins that WordPress.org's own popularity ordering lists first. The window is the trailing year, shown as a series of full weeks. Any partial final week is dropped from the series. Every week compared is complete.
How it is computed
Weekly download counts published on each plugin listing, summed across the population. Downloads include updates, so a release adds downloads from the existing install base.
How to read it
A rise or fall in download volume moves with both new installs and update activity. A release that reaches a large existing install base can lift the week's total on its own. No new user needs to install the plugin for that to happen. Read this figure beside update rate and download change for the same weeks. Together they show how much of a move traces to release activity rather than to new adoption. The figure is shown as a year-long series, so a single week reads best against the run of weeks around it.
What it is not
Download volume is not a count of active installs. It is not a count of unique users or unique sites visiting WordPress.org. It does not separate a first-time install download from an update download. A single active install can add several downloads across a year through routine updates. It also does not say whether a plugin gained or lost users, only how many download events were recorded. It is a sum across the top 12,500 plugins, not a figure for any one plugin's listing.