Test shard calculator
Enter how long your whole test suite takes, the time you want, and the setup each shard repeats. We give you the shard count and the cost.
- Shards needed
- 7
- Wall time
- 7.7 min
- target 8.0 min
- Cost per run
- $0.67
- GitHub $1.23
| Shards | Wall time | Billed min | GitHub 8 vCPU | compiler.dev 8 vCPU |
|---|---|---|---|---|
| 1 | 42.0 min | 42 | $0.92 | $0.50 |
| 6 | 8.7 min | 54 | $1.19 | $0.65 |
| 7 | 7.7 min | 56 | $1.23 | $0.67 |
| 8 | 7.0 min | 56 | $1.23 | $0.67 |
| 14 | 4.9 min | 70 | $1.54 | $0.84 |
Each job is billed in whole minutes. Prices as of October 2026.
Prices as of October 2026, from the provider's published rates. Everything runs in your browser; nothing you type is sent anywhere.
How to use it
- Enter the suite time on one machine, in minutes, without setup.
- Enter your target wall time and the setup minutes each shard pays (checkout, install, build).
- Read the shard count. The table shows how time and cost change with more shards.
Frequently asked questions
What is the formula?
Wall time = suite minutes ÷ shards + setup minutes. We solve for the smallest shard count where wall time is at or under your target.
Why is the target sometimes impossible?
Every shard pays setup. If your target is no longer than setup, no number of shards can reach it. Cut setup first, for example with caches.
What does more sharding do to my bill?
Each shard repeats setup, so billed minutes go up while wall time goes down. The table shows both.
Are shards perfectly even?
No. A real split is a little uneven. The test sharding planner balances real test durations. Add a few percent as margin.
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<p style="font-size:12px">Calculator by <a href="https://compiler.dev/tools/test-shard-calculator">compiler.dev</a></p>Related tools
- Test sharding plannerPaste test durations and split them into balanced shards. See each shard's tests, the expected wall time and the speedup before you change your CI.
- CI runner size pickerPick a Linux runner size from your test parallelism and memory needs. See vCPU, RAM and the per-minute price on GitHub and on compiler.dev.
- Cache hit savings estimatorEstimate the minutes and dollars a dependency or build cache saves each month. Enter runs, cold and warm build times and your cache hit rate.
- Monthly CI budget plannerPlan your monthly CI budget from team size, PRs a day, runs per PR and minutes per run. Compare GitHub and compiler.dev, with a cost per day.