Concurrency Calculator
Calculate required concurrency from throughput and latency using Little’s Law.
About Concurrency Calculator
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.
Formula
Concurrency
Concurrency = throughput × latency, which is Little’s Law
- Little’s Law
- Items in a system equal arrival rate times time spent in it
Worked example
With the default values below, Concurrency Calculator returns Required Concurrency of 300.0. Change any input above and every figure here is recalculated in your browser.
Inputs used
- Requests per secondminimum 0
- 2,500
- Average latencyminimum 0 ms
- 120 ms
- Headroom for peaksaccepts 0–100 %
- 30 %
- Concurrency capacity per instanceminimum 0.001
- 200
Results
- Required Concurrency
- 300.0
- Concurrency Including Headroom
- 390
- Instances Needed
- 2
- Throughput the Provisioned Concurrency Supports
- 3,333.3 req/s
- Latency Budget at This Concurrency
- 160.00 ms
Step by step
- 1Values used
- 2Concurrency
- 3Required Concurrency= 300.0
- 4Concurrency Including Headroom= 390
- 5Instances Needed= 2
- 6Throughput the Provisioned Concurrency Supports= 3,333.3 req/s
- 7Latency Budget at This Concurrency= 160.00 ms
Assumptions and limits
- The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
- In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
- Figures are rounded for display to 2 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.
Frequently Asked Questions
How is Concurrency calculated?
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.
Why does Concurrency matter?
This is why a slow downstream dependency exhausts connection pools: latency rises, concurrency demand rises with it, and the pool saturates.
What values do I need to enter?
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.