How many bytes in a packet

It depends on the protocol you are talking about, but there is also a physical limit on Ethernet which is 1500 bytes also called the MTU (Maximum Transfer Unit).

Smaller sizes can work as well.

how many bytes in a packet ,and how many packet will be provided the tx load if i have 64kbps bandwith Data Circut ,presently tx load is 247 what shoud i do

how can proved that my link is ok .. and loadis hi of branch 

MTU 1500 bytes, BW 64 Kbit, DLY 20000 usec,
     reliability 255/255, txload 247/255, rxload 15/255
  Encapsulation HDLC, loopback not set
  Keepalive set (10 sec)
  Last input 00:00:00, output 00:00:00, output hang never
  Last clearing of "show interface" counters 00:26:05
  Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 658
  Queueing strategy: fifo
  Output queue: 27/40 (size/max)
  5 minute input rate 4000 bits/sec, 7 packets/sec
  5 minute output rate 63000 bits/sec, 10 packets/sec
     14892 packets input, 1414187 bytes, 0 no buffer
     Received 182 broadcasts, 0 runts, 0 giants, 0 throttles
     0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort
     17257 packets output, 12257721 bytes, 0 underruns
     0 output errors, 0 collisions, 0 interface resets
     0 output buffer failures, 0 output buffers swapped out
     0 carrier transitions
  Timeslot(s) Used:12, Transmitter delay is 0 flags