When talking about interference there are two types: 802.11 and non-802.11 (e.g. microwave ovens, wireless microphones) The number of BSSIDs on a channel is not giving you all of the information to know how busy the channel is, in both cases.

If you are only looking at number of BSSIDs, the signal strength doesn't really matter if it's above the threshold of your devices to demodulate during DCF. You will still have to wait for that transmission to complete whether it is at -40 dBm or -70 dBm. The threshold is usually around -85 dBm to detect co-channel interference this way.

A better way to measure 802.11 "interference" is to measure airtime or channel-utilization with a tool like aircheck. However this can vary widely and change over time.

A better way to measure non-802.11 noise is to use a spectrum analyzer. Energy detected above about -62 dBm will prevent transmission, regardless of the source being 802.11 or something else.

Many enterprise WiFi solutions will include some ability to detect channel use, neighbors, noise, and client performance and adjust channel and power dynamically. In many environments this is probably easier than trying to chase these down manually and creating a static plan.

When talking about interference there are two types: 802.11 and non-802.11 (e.g. microwave ovens, wireless microphones) In both cases, the number of BSSIDs on a channel is not giving you all of the information to know the availability of a channel.

If you are only looking at number of BSSIDs, the signal strength doesn't really matter if it's above the threshold of your devices to demodulate during DCF. You will still have to wait for that transmission to complete whether it is at -40 dBm or -70 dBm. The threshold is usually at -85 dBm to detect 802.11 channel interference.

A better way to measure 802.11 interference is to measure airtime or channel-utilization with a tool like aircheck. However this can vary widely and change over time.

A better way to measure non-802.11 noise is to use a spectrum analyzer. Energy detected above about -62 dBm will prevent transmission, regardless of the source being 802.11 or something else. This type of noise is also often transient.

Many enterprise WiFi solutions will include some ability to detect channel use, neighbors, noise, and client performance and adjust channel and power dynamically. In many environments this is probably easier than trying to chase these down manually and creating a static plan.