VoLTE Capacity Calculator
Calculate maximum simultaneous VoLTE calls per cell based on available PRBs, codec selection, SPS, and Erlang B traffic model.
Technology
Remaining PRBs allocated to VoLTE
Typical: 2% (B.02)
Total PRBs in bandwidth
10 MHz 4G
PRBs available for VoLTE
After 50% data reservation
PRBs per VoLTE call
AMR-WB 12.65 — with SPS
Max simultaneous calls per cell
DL and UL independently
Erlang B traffic capacity per cell
At 2% GoS blocking — 12 circuits
Total simultaneous calls (network)
Max concurrent VoLTE calls across all cells
Busy-hour call attempts (BHCA)
Total calls the network can handle per hour
VoLTE subscriber capacity
Subscribers at 10% busy-hour VoLTE usage
VoLTE Capacity Formula
VoLTE calls share the LTE or NR spectrum with data traffic. The number of simultaneous calls is limited by the PRBs (Physical Resource Blocks) available after reserving capacity for data.
PRBs for VoLTE = total_PRBs × (1 − data_reservation%)
Max calls = floor(PRBs_for_VoLTE / PRBs_per_call)
Traffic (Erl) = Erlang_B⁻¹(max_calls, GoS%)
| Codec | Bitrate | PRBs (with SPS) | PRBs (no SPS) |
|---|---|---|---|
| AMR-NB 12.2 | 12.2 kbps | 1 | 2 |
| AMR-WB 12.65 | 12.65 kbps | 2 | 3 |
| EVS 13.2 | 13.2 kbps | 2 | 3 |
| EVS 24.4 | 24.4 kbps | 3 | 4 |
For total subscriber capacity including data users, combine with the subscriber capacity calculator. For overall RRC connection limits, see the RRC capacity calculator.
Frequently Asked Questions
What is VoLTE and how is its capacity calculated?▾
VoLTE (Voice over LTE) carries voice calls as IP packets over the LTE data bearer using the IMS (IP Multimedia Subsystem) core. Capacity is determined by how many Physical Resource Blocks (PRBs) are available for voice after reserving spectrum for data, divided by the PRBs required per call (which depends on codec and SPS). The resulting call count is then passed through the Erlang B model to find the traffic capacity at a given Grade of Service.
What is SPS (Semi-Persistent Scheduling) in VoLTE?▾
SPS pre-allocates a fixed set of PRBs to a VoLTE call at connection setup, rather than dynamically scheduling resources every TTI (1 ms). Since voice generates small, predictable packets every 20 ms, SPS eliminates per-packet scheduling overhead and reduces the control channel load. With SPS enabled, AMR-NB requires only 1 PRB per call instead of 2, approximately doubling voice capacity.
What is the difference between AMR-WB and EVS codecs?▾
AMR-WB (Adaptive Multi-Rate Wideband) at 12.65 kbps is the most widely deployed VoLTE codec, offering HD voice quality (50 Hz–7 kHz audio bandwidth). EVS (Enhanced Voice Services) is a newer 3GPP codec that delivers better quality at similar or lower bitrates and supports super-wideband (14 kHz) and fullband (20 kHz) audio. EVS also has more robust packet loss concealment. Most modern devices and networks support EVS, but AMR-WB remains the baseline fallback.
What is Grade of Service (GoS) in VoLTE dimensioning?▾
GoS is the blocking probability — the fraction of call attempts that are rejected because all voice channels are busy. A GoS of 2% (B = 0.02) means 2 in every 100 call attempts during the busy hour are blocked. The Erlang B model is used to find the maximum traffic load (in Erlangs) that a given number of channels can carry at the target GoS. Lower GoS targets (e.g. 1%) require more channels for the same traffic, increasing cost.