The simple way to assess the speed of an algorithm is to run it on the available computer and count its execution time.Key performance indicators of an encryption algorithm can be found in the link:Book Cryptology Fundamentals
The starting time and ending time can be specified in the encryption program and the difference between them gives the total time taken by the encryption algorithm. The system time setting of the computer in which the algorithm being tested is utilized for this purpose. Also, the time taken results should be accompanied with the system configurations as the values vary slightly between different configurations.
Well actually you can use any software, almost all of them have some function for measuring execution time. However, you need to mention the configuration of the machine upon which the algorithm is tested in your report because only then it would be comparable for others.