Pull Request Size
Pull Request Size measures the number of changes introduced in a single pull request (PR). It reflects how much code reviewers must evaluate at once and directly influences review quality, latency, and deployment risk.
Calculation
PR size is typically calculated by summing the number of lines added, lines removed, or total file changes in a pull request. Some teams use Git diff statistics, others apply tool-based thresholds.
This metric is recorded by evaluating the content of each merged pull request:
pull request size = lines added + lines deleted (or total changed lines per PR)
Goals
Pull Request Size helps teams track how reviewable, testable, and safe each change is. It answers questions like:
- Are we keeping PRs small enough to review thoroughly?
- Are large changes increasing merge risk or slowing delivery?
- Is our development workflow optimized for incremental integration?
Smaller PRs reduce complexity, improve review coverage, and support faster, more predictable delivery. For supporting data, see Microsoft’s study on pull request size and review outcomes.
Variations
This metric may also be called Change Set Size, Code Delta, or Diff Volume. Common segmentation strategies include:
- By team or repo, to detect variation in review practices
- By PR type, such as refactors, features, or bug fixes
- By contributor, to identify coaching or workflow opportunities
Some teams define PR size thresholds, e.g., small (under 200 lines), medium (200–500), large (over 500), and track the percentage of PRs in each category over time. Others focus on reviewed PR size, which counts only the code that received feedback.
Limitations
PR Size measures volume, not complexity, quality, or impact. A small change to a critical module may require more scrutiny than a large change to boilerplate code.
This metric also does not account for how long large PRs remain open or how well they’re reviewed. Use with caution in performance discussions, context always matters.
To better assess delivery risk and process friction, pair this metric with:
| Complementary Metric | Why It’s Relevant |
|---|---|
| Review Latency | Highlights how larger PRs delay the start of review or increase response time. |
| Cycle Time | Reveals whether large PRs extend overall development timelines. |
| Change Failure Rate | Indicates whether larger PRs correlate with more post-deployment issues. |
Optimization
Improving PR Size involves adjusting habits around task breakdown, collaboration, and integration frequency.
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Split work into smaller, logical units. Break stories into atomic, testable slices that can be reviewed and merged independently.
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Adopt Trunk-Based Development. Merge early and often to avoid accumulating large, risky change sets on long-lived branches.
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Set reviewable size guidelines. Define what constitutes a “small” PR in your team and aim for consistent formatting, clean diffs, and clear commit messages.
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Review early and incrementally. Encourage feedback on partial PRs or draft pull requests to catch design issues before code volume builds up.
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Use metrics to coach. Help teams reflect on trends in PR size and their downstream effects without using the metric as a performance proxy.
Right-sized PRs improve review quality, reduce integration pain, and accelerate delivery. When teams focus on scoping code for safety and speed, everything downstream, from testing to release, gets faster and easier.
