Stadia will work at lower resolutions, with Google recommending 20Mbps for 1080p/60fps with 5.1 surround sound, and 10Mbps for 720p/60fps with stereo sound.
That's 9GB and 4.5GB per hour, respectively, potentially using up a 1TB data cap in 114 or 228 hours.
Netflix, for example, recommends a 25Mbps connection for 4K video even though its videos generally stream at about 15Mbps.
Netflix's recommendation accounts for the actual 4K stream plus a cushion to take care of your other Internet needs.
Movies and TV are generally 24fps or 30fps instead of the 60fps that Google aims to deliver with Stadia game streaming.
We also asked Google if it will provide options for disabling 4K to reduce data use.
Karl Bode's Vice story, "Google Stadia will reveal how stupid Internet data caps are," is worth reading on this topic. »