Wi-Fi range fluctuates all the time due to network load, the speed of your router, the number of available access points and local interference from other devices. When creating a new wireless network for your home or office, establish the "real" range of the Wi-Fi network, which is the lowest value under normal operating conditions.
Find the wireless device's decibel-milliwatts (dBm) value, which you will find printed on a sticker underneath the device or in its manual.
Add 4,000 as a base value if calculating a normal antenna. Anything larger -- such as a satellite receiver or exceptionally large antenna -- will have its own specific dB value printed on the device or in its manual. If this is the case, take that dB number and add it to the numeric value calculated for the wireless device.
Subtract 2,000 to account for interference from daily signals. The interference will decrease in the evening and night, but the 2,000 value gives you a basic minimum level for peak interference.
Divide the end value by 42.7. This is the static value used for conversion to square feet in radio signal transmissions. The result you receive is the range in square feet of your signal in poor conditions. For example, 2,000 divided by 42.7 would give you a wireless signal radius range of 47 feet from the router or access point.
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If you live in a large city with many wireless networks nearby, subtract another 2,000 from the overall quality of the signal to account for extremely high interference rates.