In Wi-Fi, signal strength is measured in decibel milliwatts (dBm), which is expressed only as negative values. A perfect signal is -30 dBm, while a signal strength of -90 dBm is considered totally disconnected. The dBm scale ranges from -30 to -90, with signals measured in dBm displaying as negative numbers. A Wi-Fi signal strength of -50 dBm is considered excellent, while a signal strength of -60 dBm is good and reliable. A signal strength of -67 dBm is the minimum reading required for any online services that require a reliable connection and Wi-Fi signal strength, such as voice over Wi-Fi and non-HD video streaming. A signal strength of -70 dBm is not very strong, but mostly sufficient for light browsing and email. A signal strength of -80 dBm is unreliable and will not suffice for most services, while a signal strength of -90 dBm makes it very unlikely that you will be able to connect or make use of any services.