Since around 2014, devs and publishers have been using the number of reviews to estimate how many units any Steam game has sold. Market research and industry insights platform Video Game Insights looked into the review-to-sales ratio of over 10,000 Steam games and found out how it has changed over time.

Steam reviews have been a fairly accurate estimate for units sold, as proved by Jake Birkett, Simon Carless and others. However, Video Game Insights has found that different review multipliers should be used depending on the year a game came out.

For example, for games released before 2014, a reasonable proxy for units sold was 80 times the game’s total reviews. Right now, it is closer to 30 times.

The multiples have been changing partly in response to various tweaks to Steam’s UX, such as Steam starting to actively ask users to leave a review for a game they bought.

Below is a graph featuring review multipliers to use for the units sold estimate for Steam games by year of release.

Video Game Insights explains that “it lays out the range of multiples you should use as a proxy for games by year of release as well as the ‘best guess’ multiple to be used (the green diamond).”

“For example, Valheim, released in 2021, has 255k reviews on Steam at the point of writing this,” the analysts add. “Using the 20-55x review multiple range, we know they’ve sold between 5-14m units up to date. If we want to put a number to it, we’d use the 30x multiple – resulting in 7.7m units sold.” And this is pretty close to Valheim‘s reported 6.8m unis sold by the end of May.

This method will always have outliers. Moreover, genre and pricing impact should be factored in. But the provided ranges are accurate for over 80% of the games sutdied, according to the analysts. The platform plans to release further updates on the method in the months to come.

More information on the methed can be found in the original post by Video Game Insights.