So for a g711 call with default payload carried over ethernet:
Total Packet Size: 40 + 18 + 160 = 218 bytes = 1744 bits
PPS = 64,000 (bitrate) / 1280 (payload size) = 50
Bandwidth = 1744 * 50 = 87,200 (or 87.2 kbps)
You could also use the Voice Bandwidth Calculator from TAC:
https://tools.cisco.com/Support/VBC/do/CodecCalc1.do