VoWiFi Capacity Calculator
Find how many VoWiFi calls an access point can carry from its PHY rate and airtime efficiency, and how many APs a site needs.
Inputs
Calls per Access Point
133
Access Points Required
1
Airtime Consumed per Call
0.75%
Effective Bandwidth per Call
195.33kbps
Step by step
Values used
Usable PHY rate at the cell edge = 65 Mbps; Airtime efficiency for small voice frames = 40 %; Bandwidth per call on the wire = 87.20 kbps; Concurrent calls the site must carry = 60 calls; IPsec/ePDG tunnel overhead = 12 %
VoWiFi Capacity
calls per AP = (PHY rate × airtime efficiency) ÷ (per-call bandwidth × 2 directions), with the per-call rate inflated by IPsec overhead.
Calls per Access Point
= 133
Access Points Required
= 1
Airtime Consumed per Call
= 0.75
Effective Bandwidth per Call
= 195.33 kbps
How it works
Wi-Fi is a shared half-duplex medium, so uplink and downlink audio both consume airtime from the same budget. Voice frames are small and mostly overhead, which is why usable throughput for VoWiFi sits near 40% of the nominal PHY rate, and the ePDG IPsec tunnel adds a further per-packet cost. Access points typically fall over at 20–30 concurrent calls long before their throughput figure suggests, so airtime — not megabits — is the number that decides AP density.
Formula
VoWiFi Capacity
calls per AP = (PHY rate × airtime efficiency) ÷ (per-call bandwidth × 2 directions), with the per-call rate inflated by IPsec overhead.
- airtime efficiency
- Fraction of nominal PHY rate left after contention, retries and management frames
- 2 directions
- Voice is bidirectional and both directions share the same medium
Frequently Asked Questions
How is VoWiFi Capacity calculated?
calls per AP = (PHY rate × airtime efficiency) ÷ (per-call bandwidth × 2 directions), with the per-call rate inflated by IPsec overhead. Wi-Fi is a shared half-duplex medium, so uplink and downlink audio both consume airtime from the same budget. Voice frames are small and mostly overhead, which is why usable throughput for VoWiFi sits near 40% of the nominal PHY rate, and the ePDG IPsec tunnel adds a further per-packet cost.
Why does VoWiFi Capacity matter?
Access points typically fall over at 20–30 concurrent calls long before their throughput figure suggests, so airtime — not megabits — is the number that decides AP density.
What values do I need to enter?
This calculator takes 5 inputs: Usable PHY rate at the cell edge, Airtime efficiency for small voice frames, Bandwidth per call on the wire, Concurrent calls the site must carry, IPsec/ePDG tunnel overhead. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.