Visual Estimation is finding a value that is close enough to the right answer. It can also be defined as finding a value that is close enough to the right answer, by observation and thought.
Visual estimation can be used to estimate quantity, length, angle, area, volume and more.
Consider a red brick wall and let us try to estimate the number of bricks required to construct a similar wall very quickly.
So here we can estimate around 200 bricks in the wall as each row looks similar and in one row it looks close to 8 to 10 bricks, approximately there may be 20 rows.