How is Memory Utilization calculated for Linux server?

How is Memory Utilization calculated for Linux server?

Formula :
  Memory Utilization (%) = 100 -(((MemFree + Buffers + Cached)*100)/maxValue)
 
 In Telnet/SSH mode:
 We are using free -b command to get the memory usage for Linux server. Assume the output below,  
# free -b
             total       used       free     shared    buffers     cached
Mem:    18787995648 18667773952  120221696          0   95801344 9579597824
-/+ buffers/cache: 8992374784 9795620864
Swap:   18876977152     352256 18876624896

 Memory Utilization (%) = 100 -(((MemFree + Buffers + Cached)*100)/maxValue)
 Memory Utilization (%) = 100 - (((120221696+95801344+9579597824)*100)/18787995648) =979562086400/18787995648 = 100 - 52.13 = 47.87 = 48% (Rounded value) 
 
Memory Utilization (MB) = maxValue-(MemFree + Buffers + Cached)
Memory Utilization (MB) = 18787995648 - (120221696+95801344+9579597824)
                                 = 18787995648 - 9795620864
                                 = 8992374784 This is Bytes.
To convert this is MB    = 8992374784/(1024/1024) = 8575MB

 In SNMP mode:
 We are using UCD-SNMP-MIB file to get memory usage for Linux servers. OID's used for,
 Total Memory              .1.3.6.1.4.1.2021.4.5.0
 Free Memory          .1.3.6.1.4.1.2021.4.6.0
 Buffer Memory              .1.3.6.1.4.1.2021.4.14.0
 Cached Memory             .1.3.6.1.4.1.2021.4.15.0
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