On my route it hardly matters how "long" it is. I have put a brand new chain on, ridden 10 miles to work (at the old place). 4 miles of that is gravel road. If it's raining, I'll park the bike in the stairwell and when I get back on it in the evening, the 10 mile old chain won't bend anymore because it's entirely caked in dried clay.

I got to the point where I just power wash it and daub some lube on it when it's dirty, and put lube on when it starts making noise. I tried keeping it clean and lubed and my payoff for hours of work over the life of the chain was an extra 150 miles (about 2 weeks) life on a $6 chain. I decided diligence is overrated.

The BEST I can do, if I'm super diligent and spend hours cleaning the chain, is about 2000 miles on a chain. If I am lazy, I get 1800 miles.

I've gotten to where I don't bother measuring my chain anymore either. I just run it until it starts to skip - about 8000 miles, and then replace the entire drivetrain. It's actually LESS money than replacing the chain every 2K.