Calculate required concurrency from throughput and latency using Little’s Law.
Little’s Law ties throughput, latency and concurrency together: fixing any two determines the third. Rising latency therefore increases concurrency demand even at unchanged throughput. This is why a slow downstream dependency exhausts connection pools: latency rises, concurrency demand rises with it, and the pool saturates.
Concurrency
Concurrency = throughput × latency, which is Little’s Law
Concurrency = throughput × latency, which is Little’s Law Little’s Law ties throughput, latency and concurrency together: fixing any two determines the third. Rising latency therefore increases concurrency demand even at unchanged throughput.
This is why a slow downstream dependency exhausts connection pools: latency rises, concurrency demand rises with it, and the pool saturates.
This calculator takes 4 inputs: Requests per second, Average latency, Headroom for peaks, Concurrency capacity per instance. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.