Randolph West looks at the Azure Database Throughput Unit Calculator:
The DTU Calculator, a third-party service created by Justin Henriksen (a Microsoft employee), will calculate the DTU requirements for our on-premises database that we want to migrate to Azure, by firstly capturing a few performance monitor counters, and then performing a calculation on those results, to provide the recommended service tier for our database.
Justin provides a command-line application or PowerShell script to capture these performance counters:
Processor – % Processor Time
Logical Disk – Disk Reads/sec
Logical Disk – Disk Writes/sec
Database – Log Bytes Flushed/sec
For more details on DTUs, John Sterrett looks at the math.