Home runs used to be measured by imagination. When the announcer said a ball was hit a country mile, no further measurement seemed necessary.

Aaron Judge, whose 23 have averaged 413 feet, and thanks to precise measuring technology fans can marvel over the exact distance, such as the 495-foot shot he hit Sunday at Yankee Stadium that was the longest home run in the majors this season.

Judge’s jaw-dropping home runs have people comparing them to those of a Yankees legend who wore No. 7. History says Mickey Mantle hit 10 homers that traveled more than 500 feet, six over 600 feet and one that experts say would have traveled 734 feet had it not hit the overhang at the original Yankee Stadium.

“I hear the sky’s the limit for this kid. I hear he has big, big league power,’’ said former All-Star Frank Howard, 80, who hit his share of massive homers. Howard, who like Judge stands 6-7, said he had hit “five or six over 550 feet,” when reached this week in Aldie, Virginia.

Though there was no technology to accurately measure Mantle’s prodigious home runs that cleared stadium roofs, not just fences, fans now can get distance and exit velocity of Judge’s rockets from Statcast, where projected distance has replaced guesstimates, distance markers and brainiac mathematics. It cannot, however, forensically recalculate homers for yesteryear.

Statcast, launched in 2015, provides the distance a ball travels seconds after it lands. The radar-based system collects exit velocity, launch angle and other esoteric information. And it works whether a ball is hit into McCovey Cove in San Francisco or — maybe some day — out of Yankee Stadium.

It almost happened on May 22, 1963. Batting lefthanded, Mantle hit the facade, 565 feet from home plate. The pitch came from Kansas City Athletics righthander Bill Fischer and won the game in the bottom of the 11th inning. “Mickey’s reaction was ‘I should have hit it over a little bit, I pulled it too much,’” former teammate Bobby Richardson, 81, said from Sumter, South Carolina.

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A few feet over and the ball would have been the first and only to have been hit out of the Stadium. (Unverified stories say Negro League star Josh Gibson hit one out of the Stadium in 1934).

Paul Susman, a retired clinical psychologist in Skokie, Illinois, is an ardent Mantle fan who has written about his home runs. He said the 734-foot calculation came from the late James McDonald, a physics professor at the University of Arizona in Tucson, who had a keen interest in unidentified flying objects.

“He happened to be doing trajectory research on baseball,’’ Susman, 74, said. McDonald at the time was quoted in The Associated Press saying the ball was traveling at 155 miles per hours and 230 feet a second.

To measure Mantle’s homer, McDonald used the Pythagorean theorem, the basis for computing distance between two points, to calculate how far the ball would have traveled.

Central to McDonald’s conclusion, Susman said, was the physicist’s contention that the ball would have traveled much further had it not hit the facade. “He said it would have been 734 feet unobstructed.’’

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Christopher S. Bretherton, joint professor for atmospheric sciences and applied mathematics at the Massachusetts Institute of Technology, said, “Seven Hundred feet seems plausible if it made it all the way back to second base.’’

Fischer, who threw the home run pitch, had no doubt it would have exited the Stadium.

“It was the last part of the facade in the upper deck, the third deck, it would have went over and other people said the same,’’ Fischer, 86, said from Council Bluffs Iowa. “The ball bounced all the way back to the infield by second base. It was so devastating that it was funny. It was unbelievable that anybody could hit a ball that hard. The headline the next day was that Mantle and [astronaut Gordon ] Cooper orbit.”

In 1953, Mantle hit one out of Griffith Stadium in Washington, D.C. off Chuck Stobbs that was said to be 565 feet. A young boy picked up the ball outside the stadium. A Yankees public relations employee was said to have measured it, coining the term “tape measure home run.’’ Danny Mantle said from Plano, Texas, that he has the commemorative 600-foot tape measure given to his father.

Stobbs died in 2008, but his son Charley still remembers how it affected his father, and how he was recalled for that one home run.

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“I think later on he may have said ‘I also accomplished some things but you only keep bringing up this one. It may have ended up at 565 after it rolled down the street,’ ” Charley said.

Regardless of the exact distance, that homer was certainly memorable to then-Senators broadcaster Bob Wolff, now 96, who has been associated with Long Island’s News 12 for many years.

“Home runs usually go up and come down,’’ Wolff said. ‘When Mantle hit that it was just a line drive propelled by a strong wind and I said ‘wow did that leave the ballpark?’ There was no chance to really embellish it because it went out so fast. So when I said ‘it’s outta here,’ it is outta here.’’

On Sept 10, 1960, Mantle hit a ball out of Briggs Stadium in Detroit off Paul Foytack and it was reported to have landed 643 feet away into Brooks Lumber. “I try to forget it but I can’t,’’ Foytack, 86, said from Spring Hill, Tennessee.

“It was a monster shot, but he had a lot of monster shots,’’ said Rocky Colavito, who was in rightfield for the Tigers that night. Colavito, 83, lives in Bernville, Pennsylvania.

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Mantle’s teammate Tony Kubek remembered the slugger’s reaction. “Mickey came in, had that impish grin on his face,’’ Kubek, 81, said from Phelps, Wisconsin. “He didn’t have to say anything, but you knew that he was kind of pleased that he did it.’’

In 1985, Susman and a companion researched the Detroit homer, saying he spoke to a person who worked at the lumber store and verified the ball had been there. Susman said he and a fellow researcher used McDonald’s Pythagorean theorem to retroactively come up with the distance.

“It’s irrefutable,’’ he said. The Guinness book of records lists it as the longest home run in history at 643 feet. Neither MLB nor the Hall of Fame keep records for longest home runs.

No one can say for sure how far Mantle’s home runs went, but the lore remains. So, Judge’s homers have a ways to go before they can dismantle the feats of the Yankee legend.