What this calculator does
Amdahl’s Law estimates how much faster a task can run when part of it is executed in parallel across multiple processors, given that some portion of the task must still run sequentially.
How the calculation works
The formula is Speedup = 1 / ((1 – P) + P / N), where P is the fraction of the task that can be parallelized and N is the number of processors. The serial (non-parallelizable) portion, 1 – P, becomes the bottleneck: no matter how many processors you add, speedup can never exceed 1 / (1 – P).
This is a foundational concept in computer engineering and parallel computing, and it’s why optimizing the serial portion of a program often matters more than simply adding more cores.
Last reviewed August 2026