An estimate is what you reckon something to be when you don't have an exact number or measurement. For example, you might reckon it took 3-4 hours to finish the project.
When people say "I reckon," they're usually thinking about a rough idea or making a guess. This can happen in everyday conversations as well as in more casual writing like blogs and social media posts. Sometimes, especially when talking with friends or family, we use "reckon" informally to mean a prediction or an educated guess based on what we know so far. For instance, you might say, "I reckon it's going to rain tomorrow" if the weather forecast is uncertain. In some cases, people who live in areas where technology and infrastructure are less developed might rely more heavily on their own estimates or reckons for things like travel times or distances.
How common is "reckon"?
Word reckon is considered uncommon in modern English. It appears most frequently in fiction texts and less often in other writings.
Definitions
verb
To count; to enumerate; to number; also, to compute; to calculate.
To count as in a number, rank, or series; to estimate by rank or quality; to place by estimation; to account; to esteem; to repute.
To charge, attribute, or adjudge to one, as having a certain quality or value.
To conclude, as by an enumeration and balancing of chances; hence, to think; to suppose; -- followed by an objective clause
Example: I reckon he won't try that again.
To reckon with something or somebody or not, i.e to reckon without something or somebody: to take into account, deal with, consider or not, i.e. to misjudge, ignore, not take into account, not deal with, not consider or fail to consider; e.g. reckon without one's host
To make an enumeration or computation; to engage in numbering or computing.
To come to an accounting; to draw up or settle accounts; to examine and strike the balance of debt and credit; to adjust relations of desert or penalty.