Steam will now tell you how much space the game needs before you try to install it

Valve is making changes to Steam that will finally allow users to see how much storage a game needs without having to try to install it first. If you've signed up for the Steam Beta Client, you can take advantage of the new feature right now.

Currently, game listings on Steam show when the game was last played, how much time was spent playing the game, and the number of achievements earned:

However, in the beta version, "Last run" is missing, and instead a "Required space" tab has appeared:

If you'd like to see the changes for yourself, you'll need to sign up for the Steam Beta Program. Detailed entry instructions can be found at Steam Support, but it's a simple process: go to your Steam settings, go to the "Account" tab and click "Edit" and select "Steam Beta", wait for the update to download, restart Steam and you're done.

A source: The Verge