Estimate vs. estimation
An estimate is an approximate calculation or evaluation, and an estimation is the process of approximately calculating or evaluating. So an estimate is the result of estimation.
Of course, estimate is also a verb, and estimation can be used for any instance of the verb in action.
Examples
If the U.S. Census Bureau’s estimates are correct, Freeborn County lost about 1,700 people in the past 10 years. [Albert Lea Tribune]
Now, in the first reliable estimation of how long the volcano will continue erupting for, experts believe Lusi will not rest until 2037. [Daily Mail]
Whalen cut his estimate for this year’s revenue by about 1%, to $1.52 billion, while raising his EPS estimate by a penny to $1.24 . . . [Barron's]
Both (especially Grant) have begun a recent rise in the estimation of historians. [Wall Street Journal]