in my opinion, this is subjective to the persons idea of what that would be. I can tell you what I think is considered little and big.
when you lie for the good of the other person and not yourself, you are exhibiting a mixed motive. You have good intentions with bad execution. Especially if the lie can initially hurt someone at first.
parents tell little white lies to their kids all the time, most times so the kids will stop bugging them about something.
little lie: girl, "did you put the laundry in yet?" guy, "yeah I just did it" (he didn't do it, but is going to within those few minutes of talking to the girl)
big lie: court lawyer, "did you murder this person?" guy, "no"
obviously that is a huge extreme, but nonetheless it kind of gets my point across. Any lie that you tell that could potentially harm you, ruin your reputation, or destroy your life, is a big lie.