Estimate data used on internet calls.
Internet voice calls are extremely light in absolute terms but unusually overhead-heavy in relative terms. Because voice packets are tiny and sent every 20 milliseconds, the RTP, UDP and IP headers add roughly a third on top of the codec bitrate — a far worse ratio than bulk transfer. Even so, a full hour of calling at 24 kbps costs only around 14 MB, which is why VoIP over cellular is practically free of data concerns.
VoIP data with header overhead
Effective kbps = codec kbps x (1 + overhead); MB per minute = effective kbps x 60 / (8 x 1024); minutes per GB = 1024 / MB per minute
G.711 uses 64 kbps uncompressed, G.729 about 8 kbps, and Opus adapts between 6 and 64 kbps — typically 24-32 kbps for wideband speech, which is where most modern apps sit.
Because payloads are small. A 20 ms Opus frame at 24 kbps is 60 bytes of audio, while RTP, UDP and IPv4 headers add 40 bytes — roughly 66 percent before any link-layer framing. Longer frame sizes reduce the ratio but add latency.
No — it needs a stable one. A call uses well under 100 kbps in each direction, so bandwidth is almost never the limit. Jitter and packet loss are what degrade calls, which is why VoIP struggles on congested links that pass speed tests.