It's almost impossible to say. Last week I wrote a serializer for a specific subsystem. I spent two days screwing around; on the third day I wrote the whole thing; fixed a couple of bugs on the morning of the fourth and then refactored it a bit to improve error resilience and to integrate with some recovery routines for network transience. Friday I checked in some test routines which caused me to read through everything and tweak a couple of things in the implementation.

By then end, perhaps 1500 lines of code, but how long did I spend writing it? Four days? Three? One? (the fourth day's work ultimately didn't add many lines of code though every file was touched and had to be checked in again).