Engineering metrics glossary
Plain definitions for the numbers engineering teams get measured on. Each one says what the metric is, how it is calculated, and — the part usually left out — what it misses and how it gets misread.
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Code churn
churn, rework rate
Code churn is code that is rewritten or deleted shortly after it was written, usually within a few weeks, by the person who wrote it. It is distinct from ordinary change to old code, which is just maintenance.
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Cycle time
engineering cycle time, PR cycle time
In software delivery, cycle time is how long a change takes from the moment work starts on it to the moment it reaches production. It is the internal counterpart to lead time, which starts its clock when the customer asks rather than when the team begins.
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Defect rate
bug rate, escaped defect rate
Defect rate is how many defects reach a given stage per unit of work — commonly bugs found in production per release, per change, or per period. The version worth tracking is the escaped defect rate: the share of defects that got past every check and reached a customer.
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Flaky test rate
flaky tests, test flakiness
A flaky test is one that passes and fails on the same code, without anything having changed. Flaky test rate is the share of test runs — or of tests — that produce a different result on a rerun of the identical commit.
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Pull request size
PR size, change size
Pull request size is how much a single pull request changes, usually counted as lines added plus lines deleted, sometimes with the number of files touched alongside it. It is the strongest available predictor of how long a change waits for review.