You know it when you feel it.

“In the days leading up to it, you couldn’t wait for those games to get there,” Tino Martinez said. “When you were walking around Manhattan, or any time you entered a restaurant, there were Yankees and Mets hats all over town. If you went somewhere, Mets fans were reminding you about it.”

“I remember when we had the day-night, [two-stadium] doubleheader, [in 2003], we took the bus between games and Yankees fans were flipping us off,” Cliff Floyd said. “I was like, ‘This ain’t the World Series, people!’ ”

No, but the Subway Series, launching for the 26th season Tuesday night at Citi Field, certainly has carved out a considerable piece of real estate on the Big Apple Baseball landscape — even during unmemorable seasons like ’03, when Floyd’s Mets stunk up the city and the National League East. And in seasons like this one, when both the Yankees and Mets play well enough to create tangible visions of the actual World Series staying within the confines of the five boroughs as it last did in 2000, the excitement is palpable.

“It’s one of the things you talk about: ‘We may have to play these guys,’ ” Terry Collins said.

This sensation represents a treat rather than tradition, and let’s be honest: We can almost exclusively blame the Mets, owners of a winning record in only 12 of the 25 prior campaigns and playoff entrants just five times in the last quarter-century — as opposed to the Yankees’ 25 winning records and 21 October invitations over the same span — for such scarcity.

Perhaps, with Steve Cohen having seemingly shaken off his rookie-year owner missteps and the Yankees on pace to win well over 100 games, this 2022 high-voltage buzz can evolve into a steady hum, each year’s Subway Series a potential Fall Classic sneak preview. At this event’s silver anniversary, though, the silver lining of such infrequent Subway Series nobility means that we can more easily quantify this year’s anticipation.

Call it Subway Series Fever, the condition that persists regardless of the standings yet spikes during times of serious pennant contention on both sides of the Whitestone Bridge. Let’s scale it from 1 to 7, as a tribute to the 7 train that thousands will take to Tuesday’s ballgame, and base it on a blend of statistics, memory and historical context. When have we charted the highest Subway Series Fever readings, and how does the current case compare?

Behold the list:

“When we played them in the beginning,” Benny Agbayani said, “we were like, ‘Oh, it would be awesome to play them again in the World Series.”

Agbayani, the Mets outfielder from Hawaii, made his Subway Series debut on June 4, 1999, the seventh all-time matchup between the Mets and Yankees in the third season of interleague play. The rivalry, previously limited to Grapefruit League get-togethers and the long-gone Mayor’s Trophy Game, hit the ground running in 1997 thanks to the Yankees’ 1996 championship and the Mets, led by feisty manager Bobby Valentine, rising from the ashes of their early 1990s collapse.

“The Yankees-Mets series, in my mind, that’s what kept that interleague [play] going forward,” Martinez said.

(Random Subway Series Memory No. 1: “It’s just crazy to think about Mr. Steinbrenner and how badly he wanted us to win that series,” Martinez said, referring to the inaugural showdown in ’97. “We won two of three, but he wasn’t happy that we lost one.”)

By 2000, Year 4 of interleague ball, the Yankees reigned as the two-time defending champs, having won three of four titles. The Mets, meanwhile, had put a mighty scare into the Braves the prior October and added Mike Hampton, via a trade with Houston, to the front of their starting rotation. Just as important, the intracity foes had developed a healthy contempt for each other, best personified by the epic, mano-a-mano drama that pitted the Mets’ Mike Piazza against the Yankees’ Roger Clemens.

When you recall all of that, you can appreciate why many overlooked the ’00 Yankees’ rocky regular-season journey to their 87-74 record as well as the fact that the Mets once again placed behind the Braves (albeit by just one game), the reigning NL champions, in their 162-game trek. The fever was real. And that fever proved no false alarm when the two sides faced off again in October in a terrific World Series that played much, much closer than the final tally of 4-1, Yankees.

“You start to think, ‘We could play them,’ but it’s still June, July,” Martinez said. “What it did was, it gave us a sense of that playoff atmosphere. That atmosphere, that’s what we all played for.”

Subway Series Fever rating: 6.7

“When we were good, they hated us so bad because we were actually a good squad,” Floyd said, referring to his Mets and the Yankees fans. “I felt like those were times it played up to all the hype. That’s when it was at its best — Yankees fans screaming, ‘You stink!’ Mets fans screaming, ‘You stink!’ as well. For me, that was one of the reasons why you put on that uniform over there in Queens.”

Floyd, now a baseball analyst for the MLB Network, the Marquee Sports Network and Apple TV+, rode the Mets’ wave from their 2003 nadir (66-95) to their 2006 NL East title, when they halted the Braves’ run of 14 straight division crowns (in completed seasons) thanks to a dynamic offense and superb bullpen. Once the Mets rose again, they elevated the Subway Series; Dae-Sung Koo enjoyed his wild ride in 2005, for instance, and David Wright launched the 2006 proceedings with a walk-off single off Mariano Rivera at Shea Stadium.

Current White Sox bench coach Miguel Cairo, who played for the Yankees in 2004 and 2006-07 and the Mets in 2005, said of his Subway Series experiences, “It was unbelievable. It was like a playoff atmosphere. Every game, every pitch, with the fans in a packed park, that adrenaline was running really high.”

(Random Subway Series Memory No. 2: “I had a really good game against a lefty,” Floyd said, referencing his two-homer performance against the Yankees’ Sean Henn on June 25, 2005, in a 10-3 Mets victory at Yankee Stadium. “Willie [Randolph] said, ‘Hey, you had such a good game against the lefty, how about going [the next day] against Randy Johnson? I’m like, ‘Hell no! That ain’t him! I earned a day off against Randy!’ ” Floyd played, went 0-for-4 in the Mets’ 5-4 loss, and, he added with a laugh, “I hit a ball off my shin that I still feel.”)

At the end of the regular season, the Yankees and Mets held their leagues’ respective top playoff seeds with identical 97-65 records, the only year both teams won their divisions. Therefore, you could make a strong case for this season registering the highest Subway Series Fever. In this memory, though, it grabs the silver medal, partly because of ’06 concerns about the Mets’ starting pitching and the October cloud that hovered over the Yankees’ Alex Rodriguez — both of which came to fruition, with neither favorite reaching the finals — and partly because, man, nothing beat the Clemens-Piazza drama of ’00.

SSF rating: 6.3

The Clemens-Piazza drama began this season, specifically on June 6, just hours after Valentine and his Mets boss Steve Phillips held a most awkward Yankee Stadium news conference to discuss the firing of three coaches (Bob Apodaca, Randy Niemann and Tom Robson), as Piazza doubled off Clemens to start a four-run, second-inning rally and followed that with a two-run homer in the third. The Mets’ 7-2 win that night evened their record at 28-28 and kicked off a 40-15 run that secured Valentine’s standing as the Mets’ manager … until the Mets nearly fell out of the playoffs with a 1-8 plummet in late September.

That Mets uncertainty, coming off a 1998 that concluded with a five-game losing streak, dropping them out of the playoffs, mitigated the Subway Series Fever. That they scared the daylights out of the Braves in the ’99 NL Championship Series, climbing out of a 3-0 hole to play extra innings in a Game 6 loss, upped the Mets-Yankees excitement for the next season.

SSF rating: 5.7

The Mets’ return to relevance after the Bernie Madoff fiasco aligned with an odd Yankees campaign in which they rode an unlikely dual resurgence by A-Rod and Mark Teixeira to record their first playoff berth in three years. A three-game September set at Citi Field, as the Mets surged and the Yankees stood in strong position for an October invitation, allowed some to dream.

“That was one of the games after Matt [Harvey] said, ‘I’m not gonna pitch anymore,’ that was the game where he turned it around,” said Collins, now an analyst for SNY, referring to the Harvey innings-limit controversy of ’15. “He went five innings [on Sept. 20] and he pitched really good. He came in when the game was over and he said, ‘Look, I want to pitch.’ He got caught up in the excitement of it all, the emotions of it all. When we talk about Game 5 [of the ‘15 World Series], that was one of the reasons I left him in. He stepped up and said, ‘Gimme the baseball.’ That was a big series.”

Perhaps bigger for the Mets than the Yankees, who had seen the Blue Jays leapfrog them in the American League East standings and were limping toward the finish line, going 29-31 from Aug. 1 through the end of the regular season.

“I feel like with both [Yankees] teams I was with, they didn’t feel like World Series teams,” said Chris Young, the outfielder who played for the Yankees in 2014 (after the Mets released him) and 2015. “When I was with Boston in ’16 and ’17, both of those years, I felt like I was on a World Series-caliber team — and they ended up winning in ’18. … It’s a different energy that comes from those teams.”

(Random Subway Series Memory No. 3: “My first time playing in it was in ’14 with the Mets,” said Young, an MLB Network analyst and Apple TV+ color commentator. “I was struggling that season but I remember that series more than anything, more specifically in Yankee Stadium. I hit a big home run to take the lead (on May 12). I remember half of the Stadium going crazy.”)

SSF rating: 5.5

“Oh, sure,” recalled Ron Guidry, the Yankees’ pitching coach in 2006 and 2007, “every time you played them, you were thinking about [a Subway World Series], because it had happened before.”

The Mets for sure began their 2007 campaign thinking big, their ’06 efforts heartbreakingly falling just short of a World Series when Carlos Beltran looked at Adam Wainwright’s nasty curveball with the tying and winning runs on base. They owned a 26-14 record, best in the NL, entering the Subway Series opener May 18 at Shea.

Alas, the Yankees entered that game a lousy 18-21, well behind the Red Sox in the AL East, taking much air out of the festivities.

(Random Subway Series No. 4: “We had a lot of problems with our starting pitching [in ’07],” Guidry said. “We were minus a couple of back-end guys. So we called up this young kid, Tyler Clippard, to make his big-league debut against the Mets [on May 20]. He had this herky-jerky delivery. I thought, ‘This is either gonna be really bad or really good.’ ” It was really good; Clippard, still active in 2022 with the Nationals as a longtime reliever, threw six innings of one-run ball for the 6-2 win.)

By the time the Yankees awoke, eventually earning their 13th consecutive trip to the postseason, the Mets had fallen into a slumber, one that would ultimately produce one of the game’s worst collapses. Although if cockeyed optimists had squinted hard enough in, say, August, they might have generated some hope of an NYC-centric October.

SSF rating: 5.0

So where to fit this season? Both teams meet as division leaders, the first such confluence since their April 26, 2015, game. Both clubs appear markedly improved, with better cultures, from last season. The rehabilitating Jacob deGrom could return to the Mets’ starting rotation next week, by which time both the Mets and Yankees should be reinforced with trade-deadline imports.

“The intensity will be back there,” Martinez said. “In both stadiums, they’re going to really understand what the playoffs are like.”

If Subway Series Fever readings don’t break the thermometer, you can blame that primarily on external factors. The Yankees finished their season series against the Astros, their top nemesis of the past half-decade, with a lowly 2-5 showing, and Aaron Boone himself posed just last week, “Ultimately, we may have to slay the dragon, right?”

Whereas the Mets face the double specter of the Braves, nipping at their heels in an attempt to capture a fifth straight NL East title, and the Dodgers, the industry’s perpetual heavyweights. Shoot, when Dodger Stadium hosted last week’s All-Star Game, Los Angeles Times columnist Helene Elliott audaciously (not really) posed the possibility of a Yankees-Dodgers fall classic.

Nevertheless, as Young said, referring to deGrom and his fellow stud Max Scherzer, “If those pieces come together, this could be the [World Series] matchup.”

SSF: 6.0. Third all-time. Pretty good. Treat your fever accordingly.