If you knew all the varibles, in theory I believe you could calculate expected packet drop, but I've never seen it done in practice. The number of variables to consider is quite extensive.
For TCP, you can precompute the BDP (bandwidth delay product). Having this value provides for optimal TCP transmission rate, but won't provide information about what drops you might see in actual practice. Again, many other variables.
For actual traffic, like with routers, you could record the packets sent/received at the end hosts. However, even if they match, the sending TCP host could have thought there were drops when there were not. So you need to also look at TCP retransmissions.
e.g. (From a Windows host)
C:\>netstat -s
IPv4 Statistics
Packets Received = 66730
Received Header Errors = 0
Received Address Errors = 3
Datagrams Forwarded = 0
Unknown Protocols Received = 0
Received Packets Discarded = 274
Received Packets Delivered = 66456
Output Requests = 52088
Routing Discards = 0
Discarded Output Packets = 0
Output Packet No Route = 0
Reassembly Required = 0
Reassembly Successful = 0
Reassembly Failures = 0
Datagrams Successfully Fragmented = 0
Datagrams Failing Fragmentation = 0
Fragments Created = 0
ICMPv4 Statistics
Received Sent
Messages 8 15
Errors 0 0
Destination Unreachable 0 0
Time Exceeded 0 0
Parameter Problems 0 0
Source Quenches 0 0
Redirects 0 0
Echos 0 12
Echo Replies 8 0
Timestamps 0 0
Timestamp Replies 0 0
Address Masks 0 0
Address Mask Replies 0 0
TCP Statistics for IPv4
Active Opens = 1622
Passive Opens = 42
Failed Connection Attempts = 32
Reset Connections = 742
Current Connections = 1
Segments Received = 43329
Segments Sent = 30755
Segments Retransmitted = 37
UDP Statistics for IPv4
Datagrams Received = 21272
No Ports = 3702
Receive Errors = 0
Datagrams Sent = 21273
