Antonyms for the word "more guesstimated" could include words such as precise, exact, accurate, definite, certain, and specific. These words refer to a level of precision or accuracy that is opposite to the notion of "guesstimating," which implies a lack of certainty or precision. Other antonyms might include "measured," "calculated," "determined," "established," or "known." These words all suggest a more scientific or rigorous approach to determining a value or quantity, which is in direct opposition to the more casual, approximate, or uncertain nature of "guesstimation." Whether in business, science, or everyday life, it is often important to strive for greater precision and accuracy in our calculations and estimations.