Place access points on a floor, give each a channel and width, and watch conflicts appear. See why only three 2.4 GHz channels work together, why wide channels often lose in busy buildings, and how turning the power down can help.
Two APs on the same channel take turns
Wi-Fi devices listen before they talk. If an AP can hear another AP's transmissions on the same channel at −82 dBm or stronger, it defers while the other one sends, so the two share one channel's airtime (IEEE 802.11-2024 17.3.10.6.1). That is co-channel interference: nothing is corrupted, but everyone waits. Channels that only partly overlap, like 1 and 3 in 2.4 GHz, are worse: adjacent-channel interference corrupts frames instead of just slowing them. A good plan keeps APs that hear each other on different, non-overlapping channels.
1 · The site
Floor
Band
Rules
Coverage target
2 · The floor
Starting point: every AP on the same channel, as if nobody planned it. Press Auto-plan channels, or pick channels yourself.
Drag an AP to move it. Click one to see only its coverage and change its channel, width and power; click it again to see all APs. Each colour is one channel (see the key under the floor): APs with the same colour share airtime if a red line joins them.
Show
One AP heard on the channel2 same-channel APs heard: they share airtime3 or morePartly overlapping channels (ACI)How far the selected AP is heard (click an AP)White: no AP heard at −82 dBm
SNR 10 dB above the targetMeets the SNR targetUp to 10 dB shortWhite: too weak to use, but APs can still hear each other there (see "Where APs are heard")Same channel, they hear each otherOverlapping channels (ACI)Wall
3 · How good is the plan
The channels in use
4 · What if
Definitions
↗ opens a term's full entry in the Wi-Fi Glossary, which explains over 400 Wi-Fi terms with their IEEE 802.11 references.
Notes
From the standard: an OFDM receiver must treat the start of a 20 MHz transmission at −82 dBm or stronger as busy, and any 20 MHz signal 20 dB stronger (−62 dBm) by energy alone (IEEE 802.11-2024 17.3.10.6.1). The simulator treats two APs as sharing airtime when they share any 20 MHz channel and one hears the other at −82 dBm or more in 20 MHz: a 40, 80 or 160 MHz transmission spreads its power, so each 20 MHz gets 3, 6 or 9 dB less. The less sensitive checks on secondary channels are left out. Channel numbers and widths follow IEEE 802.11-2024 Annex E: 2.4 GHz centres at 2407 + 5n MHz, 5 GHz at 5000 + 5n MHz, 6 GHz at 5950 + 5n MHz.
Coverage target: SNR by default. The RSSI option compares signal strength alone with a target such as −67 dBm, as many designs do; it ignores noise, so it doesn't show the smaller cells of wide channels.
Coverage is SNR, not signal alone: SNR = signal − noise, and noise = −174 dBm/Hz of thermal noise (k × T: Boltzmann's constant, 1.380649 × 10⁻²³ J/K, times the standard reference temperature of 290 K, which is 4.0 × 10⁻²¹ W/Hz or −173.98 dBm/Hz; this is physics, the Johnson–Nyquist noise of any receiver, not something IEEE 802.11 defines), plus 10 × log10 of the channel width in Hz (73, 76, 79 and 82 dB for 20, 40, 80 and 160 MHz), plus a 7 dB receiver noise figure: about −94, −91, −88 and −85 dBm at 20, 40, 80 and 160 MHz. So widening a channel costs 3 dB of SNR per doubling unless the AP can send more power. The nominal width is used; the subcarriers actually in use are slightly narrower (for example 996 × 78.125 kHz = 77.8 MHz for Wi-Fi 6 at 80 MHz), a difference of 0.1–0.3 dB. Each spot counts the AP with the best SNR there.
Simplified, not a survey: signal = EIRP (transmit power + 3 dBi antenna gain) − path loss − the walls a straight line crosses, received with a 0 dBi client antenna. Path loss is free-space loss over the first metre, then rises with distance at an indoor exponent (3.0 for the office, 2.6 for the hotel, 2.4 for the warehouse; free space is 2), a common rule of thumb for clutter the walls don't cover. All this is in 2D, with no reflections, floors, people or furniture. Real buildings vary a lot; use a predictive design tool and a site survey for real designs.
Rules of thumb, not standards: wall losses (drywall about 3–5 dB, brick 8–12 dB, concrete 12–17 dB, metal racking about 8–12 dB, rising with frequency), the 7 dB noise figure, the 25 dB SNR target often used for voice and fast data, and the score. The score multiplies the average share of airtime each AP gets by the floor coverage, then takes 10 points off for each pair of APs with overlapping but different channels.
Channels: 2.4 GHz uses 20 MHz only; channels 1–13 in Thailand and Europe, 1–11 in the US. 5 GHz follows the same lists as the DFS and Radar Simulator (144 is not allowed in Europe, and 149–165 are not used for normal Wi-Fi there). 6 GHz covers 5925–7125 MHz in the US and 5925–6425 MHz in Europe and Thailand (NBTC TS 1039-2566), with low-power indoor limits on EIRP of 5 dBm/MHz up to 30 dBm (US), 10 dBm/MHz up to 23 dBm (Europe) and 11 dBm/MHz up to 24 dBm (Thailand), the same values as the Wi-Fi Channel Map. In the US a wider channel may use more power; in Europe and Thailand the cap is already reached at 20 MHz. 320 MHz, standard power and AFC are left out; 2.4 and 5 GHz power limits are well above the settings used here. Check your country's current rules.