What gauge do you need?
The thickness of speaker wire is identified by its American Wire Gauge (AWG, or "gauge") number. The lower the gauge, the thicker the wire, and the better ability to pass the amplified audio signal. You can use the following chart as a guideline:
Distance from speaker to amplifier
Less than 80 feet --- 16 AWG
80 to 200 feet --- 14 AWG
More than 200 feet --- 10 / 12 AWG