A rough calculation or appraisal is an estimate. When you hit another baseball through the kitchen window, your parents will get an estimate of the repair costs. And you should estimate being grounded for approximately 3 weeks.
An estimate is kind of like a very educated guess. Making an estimate takes good evaluation skills, and usually estimates are pretty close to the actual outcome. If the garage bill is way higher than the estimate they gave you, for example, you have a right to be angry. But if you forgot to factor in rush hour traffic when you estimated the drive from Boston to New York, that's your own fault.