Studies have shown that the productivity of a developer is about 10 LOC/day. Considering that modern software consists in millions of lines of code, this number is appalling.
Measuring productivity with LOC is of course a dangerous thing to do. With programming, quality does not correlate with quantity, and it is wise to remember the words of Dijkstra:
If we wish to count lines of code, we should not regard them as “lines produced” but as “lines spent”. — Dijkstra
Indeed, programming is not a production process but a design process. Before a piece of code reaches maturity, various directions might first need to be explored, refined, and analyzed. Qualities like readability, performance, or reliability are competing dimensions in the design space. There is rarely “one way” to program something. Effective programming is about finding the best possible tradeoff in the shortest timeframe.
Writing high-quality code requires also a high level of rigor. Code must obey the established naming conventions, idioms and patterns of the system; it must be systematically refactored to prevent technical debt to accumulate; and it must be exhaustively tested. This level of discipline pays off in the long-term, but requires more time in the short-term.
Also, as a system grows, it becomes progressively harder to maintain an accurate mental model of the system. Considerable time is thus spent assessing the existing system to temporarily reconstruct enough knowledge for the task at hand. During this time, no code is written.
One could argue that counting total lines of code is useless; what is relevant is the number of lines of code modified per commit. Lots of modifications but no additions would suggest a modular system where features can be adapted declaratively without “writing new code”. Unfortunately, metrics tools do not follow this view and treat modifications as second-class citizens.
So, is a low number of LOC/day per day good or bad? For an optimist, it might indicate a sign of code quality; the team designs carefully and takes care to write the minimum amount of code needed. For a pessimist, if might indicate that the project is stalled; you’re not delivering enough code to make the deadline. For a realist, one thing is sure: software engineering is a very expensive activity.
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