Learner's definition of ESTIMATION
a judgment or opinion about something
My estimation of his films was never very high. [=I never thought his films were very good]
This is not, in my estimation, an efficient use of our resources.
She went down in her supporters' estimation after she voted against the plan.
the act of judging the size, amount, cost, etc., of something
the act of estimating something
a guess about the size, amount, cost, etc., of something