Note: some RF engineers recommend -65dBM as the lowest signal level for maximum performance.

"Walls and other obstructions—including but not limited to human bodies, cabinets and furniture, and appliances—will attenuate the signal further. A good rule of thumb is -3dBM for each additional wall or other significant obstruction, which we'll talk more about later. You can see additional curves plotted above in finer lines for the same distances including one or two additional walls (or other obstacles)."

Ten rules for placing your Wi-Fi access points