Playbook Runtime Calculator

Estimate total Ansible playbook execution time across tasks, hosts and forks.

About Playbook Runtime Calculator

Ansible processes hosts in parallel batches sized by --forks; each task must complete across the current batch before the next task starts, so total runtime is driven by the number of batches, not the raw host count. Formula: runtime = ceil(hosts / forks) × tasks × avg_task_duration + fact_gathering_time. Increasing forks reduces the number of batches (up to the point where forks ≥ hosts, i.e. full parallelism in one batch).

Formula

runtime_sec = ceil(hosts / forks) × tasks × avg_task_duration + ceil(hosts / forks) × fact_gathering_per_batch

hosts: Number of target hosts
forks: Ansible parallelism (--forks)
tasks: Number of tasks in the playbook
avg_task_duration: Average seconds per task per host
fact_gathering_per_batch: Seconds for fact gathering per batch

Worked example

With the default values below, Playbook Runtime Calculator returns Estimated Playbook Runtime of 12.83. Change any input above and every figure here is recalculated in your browser.

Inputs used

Host Countaccepts 1–1,000,000 hosts: 100 hosts
Task Countaccepts 1–100,000 tasks: 25 tasks
Avg Task Durationaccepts 0.1–3,600 sec: 3 sec
Forks (Parallelism)accepts 1–10,000 forks: 10 forks
Fact Gathering Timeaccepts 0–600 sec per batch: 2 sec per batch

Results

Estimated Playbook Runtime: 12.83 min
Estimated Playbook Runtime: 770.0 sec
Parallel Batches: 10
Speedup vs Serial (forks=1): 9.74 ×

Step by step

1Parallel batches: ceil(hosts / forks)= 10 batches
2Task execution time: batches × tasks × avg duration= 750.0s
3Fact gathering time: batches × per-batch duration= 20.0s
4Total runtime= 770.0s (12.83 min)

Assumptions and limits

The result is derived only from the 5 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

What's a good forks value?

Ansible's default is 5, which is conservative for most use cases. Values of 20-50+ are common in production for large fleets, limited mainly by the control node's CPU/memory/network and how much load you're willing to put on target hosts simultaneously.

Why does fact gathering add time per batch, not per host?

Fact gathering (the implicit 'setup' task) runs in parallel across each batch just like any other task, so its cost is incurred once per batch of forks hosts, not once per individual host — this calculator models it as a fixed per-batch cost.

How can I speed up a slow playbook beyond increasing forks?

Disable fact gathering when not needed (gather_facts: false), use free strategy instead of linear to avoid waiting for the slowest host in each batch, enable pipelining, and use async/poll for long-running tasks.

Does network latency to hosts affect this estimate?

Yes — 'avg task duration' should include SSH connection and round-trip overhead, not just module execution time; measure this from real playbook runs (ansible-playbook -vvv or callback plugins) for an accurate baseline.