Real Dictionary

estimate
verb: If you estimate a quantity or value, you make an approximate judgment or calculation of it.

estimate in American English
a general calculation of size, value, etc.; esp., an approximate computation of the probable cost of a piece of work made by a person undertaking to do the work
to form an opinion or judgment about
to make an estimate or estimates
intransitive verb: to make an estimate
noun: an approximate judgment or calculation, as of the value, amount, time, size, or weight of something
transitive verb: to form an approximate judgment or opinion regarding the worth, amount, size, weight, etc., of; calculate approximately

estimate in British English
verb: to form an approximate idea of (distance, size, cost, etc); calculate roughly; gauge