Multistream bandwidth calculator
How much upload a multistream actually needs, and how much traffic it moves in a month. The answer depends less on the bitrate than on where the copying happens: from a desktop encoder every destination is another connection leaving your house, while a cloud Fan-out sends the video up once.
Your stream
What it costs
The per-destination figure is the traffic the stream moves; on a cloud service it moves from the datacentre, not from you, so what leaves your connection is the video library - uploaded once, however many platforms it reaches. Audio is counted at 160 kbps on top of the video bitrate. Two platforms end a broadcast themselves - Facebook at 8 hours, Twitch at 48 - so hours live per day is about the schedule, not about a single unbroken session; the platform limits table has the detail.
Let the fan-out happen somewhere else
Upload the videos once and reach up to ten platforms from one broadcast, without any of it crossing your own connection.
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Only if the copying happens on your machine. OBS with a multi-RTMP plugin encodes once and then opens one connection per platform, so three destinations at 6,000 kbps is 18 Mbps leaving your connection continuously. A cloud service receives the video once and opens the connections itself, so your upload carries one file rather than N streams.
About 2 TB per destination per month at 6,000 kbps running continuously - the arithmetic is bitrate times seconds, and it matches what we measure on our own workers. Three destinations is therefore around 6 TB a month, which is where residential fair-use policies start to matter if the fan-out is happening at home.
Barely. The video is encoded once and the packets are copied to each destination; measured on our workers, one destination costs 9.7% of a core, two 11.9% and three 13.0%. Running them as separate encoders instead costs about 1.9x, because the audio encoder then runs per output. Bandwidth scales linearly; processing does not.
The lowest ceiling among your destinations. 6,000 kbps at 1080p sits inside YouTube's, Twitch's and Kick's recommendations and at the top of Facebook's range, which is why it is the default here. The bitrate calculator turns your measured upload speed into a number you can hold instead.