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.
About VoWiFi Capacity Calculator
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
Worked example
With the default values below, VoWiFi Capacity Calculator returns Calls per Access Point of 133. Change any input above and every figure here is recalculated in your browser.
Inputs used
- Usable PHY rate at the cell edgeaccepts 6–2,000 Mbps
- 65 Mbps
- Airtime efficiency for small voice framesaccepts 5–80 %
- 40 %
- Bandwidth per call on the wireaccepts 10–500 kbps
- 87.2 kbps
- Concurrent calls the site must carryaccepts 1–10,000 calls
- 60 calls
- IPsec/ePDG tunnel overheadaccepts 0–60 %
- 12 %
Results
- Calls per Access Point
- 133
- Access Points Required
- 1
- Airtime Consumed per Call
- 0.75%
- Effective Bandwidth per Call
- 195.33 kbps
Step by step
- 1Values used
- 2VoWiFi Capacity
- 3Calls per Access Point= 133
- 4Access Points Required= 1
- 5Airtime Consumed per Call= 0.75
- 6Effective Bandwidth per Call= 195.33 kbps
Assumptions and limits
- The result is derived only from the 5 inputs listed above. Anything not among them is not part of the calculation.
- In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
- Figures are rounded for display to 2 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.
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.