estimate
This formula gives you a rough estimate of the amount of fertilizer you will need.
Rough estimates suggested that around a million people could have received emails with attachments containing the virus.
He enclosed a note, explaining that it was only a rough estimate of the cost.

SMART Vocabulary: related words and phrases

Guesses and assumptions
a shot in the darkidiom
approximation
assumption
bet
conjecturally
conjecture
counterfactual
estimate
misassumption
misestimate
misestimation
overestimate
overestimation
proposition
purportedly
re-estimate
sneaking
speculation
speculatively
suspicion