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Connection Pool Size Calculator

Work out connection pool size instantly with clear inputs, formula shown and shareable results.

About Connection Pool Size Calculator

Pool size should follow concurrency, not thread count. Queries in flight is query rate times query duration, so 1,200 queries per second at 8 ms each needs only about 10 concurrent connections. Oversized pools are actively harmful: they let more work reach the database than it can execute, converting fast queueing in the application into slow contention in the database.

Formula

Pool sizing

query rate = requests per second x queries per request; concurrent = query rate x query time; pool = ceil(concurrent x 1.5), capped by thread count

Worked example

With the default values below, Connection Pool Size Calculator returns Recommended pool size of 15. Change any input above and every figure here is recalculated in your browser.

Inputs used

Application threadsminimum 1
40
Average query timeminimum 0.01 ms
8 ms
Requests per second per instanceminimum 0.01
300
Queries per requestminimum 0.1
4

Results

Recommended pool size
15
Queries in flight
9.60
Query rate per instance
1,200 q/s
Pool utilisation
64.0%

Step by step

  1. 1Values used
  2. 2Pool sizing
  3. 3Recommended pool size= 15
  4. 4Queries in flight= 9.60
  5. 5Query rate per instance= 1,200 q/s
  6. 6Pool utilisation= 64.0

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

Is a bigger pool safer?

No. Beyond the database's own parallelism, extra connections add context switching and lock contention. Small pools with queueing usually give better throughput and much better tail latency.

How does this interact with the database connection limit?

Pool size multiplied by instance count must stay under the server limit, leaving headroom for administrative sessions and replicas.

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