It would be delivering a blow whose magnitude could not be reckoned until it struck.
Newt was—again and for the moment—a power to be reckoned with.
They were there to put on a show and deliver a message: behold, we are a technological power with which to be reckoned!
The novel was inspired by many real-life events—more than I reckoned for when I first starting thinking about it.
Instead, the Know-Nothings were briefly a force to be reckoned with.
When not carried to the treasury, they were reckoned invalid.
Farewell, now, to the sergeant's stripes, on which I had reckoned so surely!
Chlan, who reckoned on carrying so young a man by storm, talked a great deal.
Our absence from the vessel was reckoned at five or six days.
The distance to which a shot was reckoned to range straight, without appreciable drooping from the force of gravity.
c.1200, recenen, from Old English gerecenian "to explain, relate, recount," from West Germanic *(ga)rekenojanan (cf. Old Frisian rekenia, Middle Dutch and Dutch rekenen, Old High German rehhanon, German rechnen, Gothic rahnjan "to count, reckon"), from Proto-Germanic *rakinaz "ready, straightforward," from PIE *reg- "to move in a straight line," with derivatives meaning "direct in a straight line, rule" (see regal).
Intransitive sense "make a computation" is from c.1300. In I reckon, the sense is "hold an impression or opinion," and the expression, used parenthetically, dates from c.1600 and formerly was in literary use (Richardson, etc.), but came to be associated with U.S. Southern dialect and was regarded as provincial or vulgar. Related: Reckoned; reckoning.