If you’re on a 3G connection, you&’ll be served a lower-quality stream to help buffering. The low quality video also means less data, and in our testing, only consumed 27.1MB.
When streaming Netflix over LTE the difference in cellular data usage is ridiculous. The video that was streamed during the test racked up 79.6MB of data. The high-quality video wasn’t even noticeably better than 3G to warrant the heavy data consumption. It’s also important to note that the auto-quality feature can be disabled through the online account settings on the Netflix website.
Read more //mashable.com