Estimate data used on video calls.
A video call carries one outgoing stream plus one incoming stream per other participant, so data scales with the size of the meeting rather than being fixed per call. That is why a two-person call is light and an eight-person gallery view is heavy. Turning your camera off removes your outgoing stream; going audio-only removes all of them and drops usage to roughly half a megabyte a minute.
Call data by participant count
Streams carried = participants; MB per call hour = streams x MB per minute per stream x 60; monthly GB = MB per hour x hours x days / 1024
Roughly 500-800 MB for a one-to-one HD call and 1-2 GB for a group call of five or six in gallery view. Screen sharing adds less than a camera stream because static slides compress extremely well.
It removes one stream out of however many are running. In a five-person call that is about a fifth of the total, and it also saves upstream bandwidth, which is usually the scarcer direction on cable and DSL connections.
Because they stop sending full-resolution video for every participant. Most switch to a single active-speaker stream at full quality plus low-resolution thumbnails, so very large meetings scale far better than the linear estimate suggests.