Does Size Really Matter? Pull Requests and Lines of Code

Size matters — at least when it comes to pull requests (PRs) in software development. As research shows, smaller is often better when it comes to lines of code (LOC) and the number of features in a PR. Let’s explore why.

Research About the Size of Pull Requests

Research consistently shows that smaller pull requests (PRs) are associated with fewer bugs, faster and higher‑quality reviews, and better reviewer engagement than large PRs. Most empirical and industry data points toward “small, coherent, incremental” PRs rather than squeezing as much as possible into one large PR.

Bugs and Defect Detection

SmartBear’s large Cisco study found that defect detection is highest when each review covers roughly 200–400 lines of code (LOC); beyond about 400 LOC, reviewers are overwhelmed and miss more defects.​

A recent data study reports that PRs in the ~200–400 lines changed range have about 40% fewer post‑merge defects than larger PRs, and PRs over 1,000 lines can have defect detection rates less than half of small PRs.​

Metrics analyses of many teams show that “elite” teams tend to keep PR sizes under roughly 200 lines/changes, while struggling teams routinely work with PRs several times larger, with correspondingly more quality issues.

Review Quality and Speed

Controlled and field studies indicate that review effectiveness drops sharply as the amount of code per review grows; SmartBear recommends reviewing 200–400 LOC in about 60–90 minutes for 70–90% of defects found.​

Observational data from engineering analytics shows that as PR size grows, review latency increases and the chance of superficial “LGTM” reviews rises, which reduces useful feedback and defect discovery.​

Teams that consistently keep PRs under ~400 lines see substantially faster review cycles (often around 3× faster approvals) compared with large PRs.

Reviewer Engagement and Participation

Larger reviews correlate with fewer “useful” comments per line changed; once a review includes many files or large diffs, reviewers provide less actionable feedback per unit of code.​

Smaller, focused PRs reduce cognitive load, making it easier for reviewers to fully understand the change and engage with more specific, high‑quality comments.​

Frequent, incremental PRs encourage more regular interaction and collaboration, while very large PRs can discourage reviewers from volunteering or cause delays as people defer the heavy review.

Typical Size “Sweet Spots”

Different sources converge on similar magnitude guidelines rather than a single magic number.

Practical guidelines: bug fixes under ~100 lines, small features around 200–400, single‑purpose refactors 300–500, keeping each PR logically cohesive.

SmartBear / Cisco: 200–400 LOC per review, with strong warnings above 400 LOC.​

Several modern analytics and tooling vendors: “most effective” PR sizes under roughly 200–400 changed lines, with elite teams around or below ~200 changes per PR.​

Strategy: large vs small PRs

Overall, evidence favors small, coherent PRs over large, all‑inclusive ones.

• Large PRs:
  • Increase review time and latency, reduce defect detection, and tend to produce shallow reviews.​
  • Make it harder to isolate the cause of regressions, and authors are often more resistant to rework after investing heavily in a large change.​
• Smaller PRs:
  • Improve review depth, reduce bugs, and speed up integration and deployment.​
  • Make it easier to track behavior changes and roll back safely if a problem appears.​

Other Considerations

Rollbacks

It is common for pull requests (PRs) to be merged into the main branch using the squash strategy, where all commits in a PR are combined into a single commit before merging.

If a squashed PR contains multiple features and one of them introduces a bug, reverting only the buggy feature becomes difficult. You would either need to revert the entire squashed commit—which may remove working features and impact users—or manually create a new PR to remove the problematic code, which is error‑prone and time‑consuming.

By contrast, if each PR implements only one feature, reverting a specific feature is straightforward: you can simply revert the corresponding squashed commit.

Developer Productivity

Some organizations use the number of commits to the main or trunk branch as a measure of developer productivity. This means a developer can appear more productive by splitting large pull requests into multiple smaller ones, since each PR results in separate commits that make it look like more work was produced than a single larger PR.

This is an incomplete and often misleading way to measure productivity, but it is still used in practice, so understanding it is useful for individual contributors. Organizations sometimes reward a higher number of commits instead of more meaningful outcomes, such as impactful features or fewer bugs.

The best organizations typically design their own multidimensional productivity metrics that combine several KPIs, such as commits, lines of code, defects, features delivered, communication quality, feedback given and received, review latency, participation in reviews, and other indicators of impact and collaboration.

Conclusion

Prefer many small, self‑contained PRs over one huge PR, especially for features that can be sliced along clear boundaries (e.g., schema, backend, UI, tests).​

Aim for PRs that:

• Can be understood and reviewed in under about an hour.
• Touch a limited number of files and represent a single logical change or concern.
• Stay roughly within the 200–400 LOC band for typical work, smaller for bug fixes.​

Use process and tooling (branching strategy, CI, automated checks, size warnings) to discourage overly large PRs except when truly unavoidable.

In summary, the research and large‑scale field data are aligned: break work into smaller, cohesive PRs rather than packing everything into one big review if you care about bugs, review quality, and engagement