Chris Done’s estimation method is brilliant because it allows for flexibility and grows with the complexity of what you are estimating.

I call it “less than estimation” because if a given piece of work is obviously under an hour, your estimate is <hour. If it’s not obvious, you bump it up to <day. If it doesn’t obviously fit within a day, bump it up to a <week. If you’re not sure it’ll fit into a week, my experience says that it could take even three weeks, so bump it up to <month.

— Less-Than Estimation

This should also work well with your preferred task manager if it allows you to use tags to add meta-data to tasks.