We know the Mets’ rotation is special. But I wanted to know how special. So I tried to quantify it, and this is what I came up with:

The Billion-Dollar Rotation.

My question: If Jacob deGrom, Matt Harvey, Noah Syndergaard, Steven Matz and Zack Wheeler were made free agents this offseason, how much would they receive collectively?

I thought deGrom, Harvey and Syndergaard would all obtain contracts in the $250 million range, Matz at about $150 million and Wheeler at $100 million. Add it up and it is $1 billion. Yep, with a “b.”

Six current or former front-office executives were contacted and five agreed the group would haul in about $1 billion in total. As one NL head of baseball operations said: “I do think $1 billion is a reasonable estimate. Certainly, their top four [all but Wheeler] would be more appealing than most, if not all, of the pitchers who changed teams this offseason.”

An AL head of pro scouting said: “We could argue specifics on each player, but I would have to think you’d get to a billion one way or another.”

The key here is teams would be bidding for not just, in the words of one NL GM, “absurd talent,” but the kind of youth that hardly ever shows up in free agency. DeGrom is the oldest at 27; Harvey is the closest to actual free agency and that is three years away.

What would hurt their markets is that all but Syndergaard already have undergone Tommy John surgery and there is sentiment in the game that there is just a certain span likely between having one procedure and the need for another. And Syndergaard’s power stuff would put him — unfortunately — high on the list of pitchers likely to need Tommy John in the future.

However, this free-agent bazaar — or should it be bizarre? — has exemplified how far teams will go to secure talented starters. David Price got the most ever for a pitcher, $217 million over seven years, and his record for annual value did not even last a week before Zack Greinke was given a six-year deal at $206.5 million that pays him through age 37.

Johnny Cueto got $130 million despite persistent concerns about his elbow. Jordan Zimmermann got $110 million, though there was general agreement his stuff was down last year. Jeff Samardzija got $90 million and was among the majors’ worst full-time starters in 2015.

Ten free-agent starters had signed multi-year contracts through the weekend totaling $875 million. Add in the five more one-year deals (including for Bartolo Colon, who will be a placeholder in the Mets rotation until Wheeler returns) and it is $918.05 million.

The total for those 15 starters falls short of what, I believe, the Mets’ five would receive. My estimate and that of almost all my panel was that deGrom, Harvey and Syndergaard would top Price’s figure. In fact, it was not out of the question because of their youth that they could get eight-, nine- or even 10-year deals. Four of the six executives actually said because of Syndergaard’s age (23), health and ceiling, he would receive the largest contract (“easily the most” in the words of the NL GM). The other two said deGrom because of track record.

The sport-wide love for Matz is stark, though he has started just nine games (including three in the playoffs) and had TJ surgery. However, he is a 24-year-old lefty who throws in the mid-90s with poise. There is no guesswork about that because he has done it in the majors.

The Red Sox, for example, invested (in salary and tax) $135.5 million in Cubans Rusney Castillo and Yoan Moncada, not sure when they would play in the majors and at positions less valuable than lefty starter. I am sure Boston (and many clubs) would invest at least that much in Matz by himself — probably more.

As for Wheeler, yes, he is not due back from TJ surgery before June or July. But he is just 25 and has already demonstrated at least No. 3 starter ability, and I would think most (if not all) of the 30 teams would spend $90 million or more to have Wheeler rather than Samardzija.

Whether Wheeler would get $75 million or Syndergaard perhaps $300 million, the end result is the Mets have en masse what teams are bidding like mad to try to procure this offseason — prime-aged, high-end starters.

Which does apply some pressure on the organization to capitalize on this moment. With only Harvey arbitration-eligible, the quintet will be paid roughly $8 million in 2016. That will rise significantly and steadily in future years, and so will the risk of injury and decline in performance.

For now, though, because they have five 20-somethings with such high ceilings, the Mets have what one NL player-personnel head called “a unique, amazing rotation.”

Shelby Miller would be no better than the Mets’ fourth starter and a year from now might fall behind Matz and Wheeler, too. Yet to land Miller, the Diamondbacks were willing to give up the No. 1 pick in last June’s draft (Dansby Swanson), a good two-way outfielder (Ender Inciarte) and well-regarded pitching prospect (Aaron Blair).

With the hunger for starters, should the Mets — looking at a free-agent market that did not have the shortstop or center fielder they needed — try, for example, to trade Syndergaard for Arizona center fielder A.J. Pollock or Harvey for Boston shortstop Xander Bogaerts and buy a starter anywhere from Mike Leake to Price in free agency to keep the rotation deep and strong?

But even as currently constituted, the Mets are contenders because they have what every other organization dreams about: the Billion-Dollar Rotation.