Overall speedup from a parallel fraction and how many times faster that part runs.
| Speedup | – |
Use this calculator to see how much a program speeds up when only a share of the work can run in parallel. Enter the parallel fraction p (0 to 1) and the speedup s of that part.
Speedup = 1 / ((1 − p) + p / s). 80% parallel on 4 cores is 1 / (0.2 + 0.2) = 2.5×, not 4×. Serial leftovers cap the gain. p must stay between 0 and 1; s must be positive.
This is Amdahl's law for a single workload, not Gustafson scaling or a measured benchmark.
Parallel fraction: Share of the work that can run in parallel, 0 to 1.
Processors: How many times faster that parallel part runs.
Speedup: Overall speedup of the whole job.
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