As far as or approaching a certain point. For example, The water was nearly up to the windowsill, or They allowed us up to two hours to finish the test, or This seed should yield up to 300 bushels per acre. [c. a.d. 950]
be up to. Be able to do or deal with, as in When I got home, she asked if I was up to a walk on the beach. This usage is often put negatively, that is, not be up to something, as in He's not up to a long drive. [Late 1700s]
Occupied with, engaged in, as in What have you been up to lately? This usage can mean "devising" or "scheming," as in We knew those two were up to something. It also appears in , meaning "occupied with or devising something harmful," as in I'm sure those kids are up to no good. [First half of 1800s]
Dependent on, as in The success of this project is up to us. [c. 1900] Also see the following idioms beginning with up to.