For a routine, well-scoped pull request (PR), one accountable reviewer is a reasonable default. Add another when the change needs a distinct area of expertise or independent scrutiny—not simply to collect another approval. No universal evidence-based reviewer count fits every team.
How many reviewers should a pull request have?
Start with one reviewer who understands the affected code. For changes with greater consequences or multiple areas of ownership, request additional review only when another person can assess something meaningfully different.
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This is a practical rule, not a proven formula: available studies do not establish that one or two reviewers is optimal for every organization, or tie a particular risk level to a required count.
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A 2018 Google study combined 12 interviews, a survey of 44 respondents, and review logs for 9 million changes. In that process, the median number of reviewers was one, and fewer than 25% of changes had more than one reviewer. The authors also discussed earlier cross-project research that found two reviewers in the systems it studied. These findings describe different environments; they do not establish a universal best practice. Google Research’s study page and the paper provide the details.
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A 2023 review-speed article associates smaller changes with more effective review, but does not provide a formula for reviewer count. Keep a change small enough to understand; adding reviewers does not make an overly broad change easier to assess. The 2023 article discusses review speed and effectiveness.
When to request one reviewer or more
| Pull request | Reviewer approach | Reason |
|---|---|---|
| Routine, low-risk, self-contained change | One reviewer familiar with the affected code | A single accountable reviewer can provide focused scrutiny. |
| Change to an owned subsystem | Request the relevant code owner; add another reviewer only for a separate needed check | Ownership routes review to the people responsible for that code. |
| Security-sensitive, data-integrity, cross-service, or otherwise consequential change | Consider a second reviewer who brings distinct expertise or an independent check | Additional review is useful when it covers a real gap, not when it duplicates the first review. |
| Broad or difficult-to-understand change | Consider splitting it into smaller changes before adding reviewers | More reviewers do not remove the burden of understanding an oversized change. |
This table is operational guidance inferred from the evidence and review-platform capabilities, not a set of risk categories tested in a study.
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How GitHub handles approvals and code owners
GitHub distinguishes general review requirements from code ownership. Reviewers can comment, suggest changes, approve, or request changes. Repository administrators can require approvals, while a CODEOWNERS file can automatically request review from the people or teams responsible for changed files. When code-owner approval is required, GitHub says approval from any one applicable owner is enough to satisfy that ownership requirement; repository settings determine the overall approval rules. See GitHub’s pull request review documentation and documentation about code owners.
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These controls answer different questions: an approval rule sets how many approvals are required, while code ownership identifies who should review particular files. A team can use ownership rules to obtain specialist input without requiring multiple general approvals on every PR.
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How to decide whether your team needs two approvals
When setting a repository-wide requirement, compare the value of another independent check with the cost it adds to review time and workload. Track whether reviews uncover substantive issues and whether defects appear after merge; raw comment counts alone do not demonstrate quality.
- Error consequences: Could a mistake cause a serious security, data-integrity, or service-impact issue?
- Distinct expertise: Does the second reviewer understand a different subsystem, operational concern, or specialist area?
- Review capacity: Will another required approval create delays or draw work away from other reviews?
- Observed outcomes: Are additional approvals finding meaningful issues or improving outcomes, rather than duplicating comments?
If a policy requires two approvals for every change, examine whether the second approval consistently adds independent scrutiny. A blanket rule can cause delay, duplicate feedback, or approvals that provide little additional review; whether those costs are worth it depends on the repository and its risks.
FAQ
Should every pull request require two reviewers?
No universal evidence establishes that every PR needs two reviewers. A team may set that policy, but a second approval is most useful when it contributes expertise or scrutiny that the first reviewer does not provide.
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GitHub’s documentation says that, when code-owner approval is required, approval from any one applicable owner satisfies that ownership requirement. Whether it also meets a repository’s general approval requirement depends on the configured rules.
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