COCOMO is an impressive project and I wish someone would update it with modern projects to see if/how things have changed. But the main rule of thumb I brought

COCOMO is an impressive project and I wish someone would update it with modern projects to see if/how things have changed. But the main rule of thumb I brought from COCOMO was that it takes 5 person-days to get 100 lines of code from idea to production. That has been remarkably accurate in my experience. I've witnessed high-performing teams do 125 lines in 5 days, and low-performing teams doing 60 lines in 5 days, but it's still well in the ballpark.