IT-02

Wi-Fi Coverage & Capacity

IEEE 802.11 · ITU-R P.1238 · ANSI/BICSI 008-2024 · ANSI/BICSI 007-2024 · IEEE 802.3af / at / bt

01 · Environment

Band

Building typeⓘ

Floor area per floor

m²

Number of floors

02 · Radio link budget

AP transmit powerⓘ

dBm

Antenna gain

dBi

Target RSSI at the cell edgeⓘ

dBm

Client receive sensitivityⓘ

dBm

03 · Capacity

Concurrent clients

Throughput per clientⓘ

Mbps

Channel width

Spatial streams

Airtime efficiencyⓘ

Awaiting input13 fields left: Band · Building type · Floor area per floor · Number of floors · AP transmit power · Antenna gain · Target RSSI at the cell edge · Client receive sensitivity · Concurrent clients · Throughput per client · Channel width · Spatial streams · Airtime efficiency

Capacity and layout

The drawing appears when the inputs are complete

01
Size access point count from ITU-R P.1238 indoor propagation and from client capacity demand, whichever binds, with channel reuse and per-client throughput checks.
02
Tip. Count access points twice — once for coverage and once for capacity — and take the larger. In a dense space capacity almost always wins, and an installation designed only for coverage will show full signal bars while nobody can hold a call.
03
N = 30 — ITU-R P.1238 office, 2.4 GHz
04
N = 31 — ITU-R P.1238 office, 5 GHz
05
−67 dBm — Typical design RSSI
06
20 % — Cell overlap for roaming

Coverage and capacity planning

An access point count has two answers and you need the larger. Coverage asks how far the signal reaches before it drops below the usable threshold; capacity asks how many clients one radio can serve at the throughput they expect. In a dense space capacity almost always wins, and a design done on coverage alone shows full signal bars while nobody can hold a call.

Propagation and coverage

Indoor path loss is modelled by ITU-R P.1238, whose distance exponent varies by building type. Construction materials, clutter and mounting position all subtract from the usable range.

Use cases

N = 30 for office at 2.4 GHz, 31 at 5 GHz
Design RSSI typically −67 dBm for voice
Cell overlap of about 20 % supports roaming
6 GHz reaches materially less far than 5 GHz

Formula

L = 20·log₁₀(f) + N·log₁₀(d) + Lf(n) − 28

ITU-R P.1238 · IEEE 802.11

Capacity and airtime

Each client consumes airtime rather than bandwidth. Slower and legacy clients occupy the medium for longer at the same payload, which is why device mix matters more than headline PHY rate.

Use cases

Clients per AP × per-client throughput sets the load
Concurrency — not everyone transmits at once
Keep AP load below about 70 % of capacity
N+1 spare capacity avoids holes when an AP fails

Formula

APs = client count × per-client Mb/s ÷ usable AP throughput

ANSI/BICSI 008

Airtime efficiency, device mix factors and per-client throughput are planning assumptions, not standards, and this tool flags them as such. No desktop calculation replaces a predictive survey against the real floor plan, and none replaces a validation survey after installation.