You’ve heard of girl math, but what’s Philly math? The TikToker who invented it explains.

Forget algebra or calculus. The greatest minds of our generation are now flummoxed by “Philly math.”

Coined in a TikTok by Philly lifer Stephanie Powley — who goes by @stephunnyjane on the platform — Philly math refers to “the things that only make sense to us, the people who grew up here,” Powley told The Inquirer.

In a video posted to TikTok Sunday that has since been viewed more than 16,000 times, Powley ran through the essentials equation and calculations of Philly math, which include the simplistic “Go Birds equals everything” and the more complex “13 + 1 = Broad,” which refers to the city’s lack of a 14th Street.

“Philly math is getting a ticket from the PPA and just never going back to that neighborhood again because … then you don’t have to pay it,” Powley, 39, explains in the video. “Philly math is knowing the exact speed you need to go on the Boulevard to not get a ticket.”

Philly math is connected to girl math, or the complicated psychological economics women (and men!) often do to rationalize their spending, like considering a purchase made in cash “free” because it didn’t come out of your checking account or a refund from a return as surprise income.

Philly math, girl math, and their siblings, boy math and boomer math, are part of a larger social media trend of pithy meme formats that essentialize what it means to be a person, or a girl, or even a Philadelphian.

“Girl math is pretty logical, but Philly math borders on illogical,” Powley said. “When you do Philly math, you’re still left confused.”

Powley gets into more advanced formulas in the second Philly math lesson she posted to TikTok on Monday.

“Philly math is being able to tell how long someone has had their [phone] number by their area code,” Powley said. “Philly math is using someone’s favorite cheesesteak place to determine their personality.”

Powley, who lives in the Far Northeast and grew up in Northwood and Rhawnhurst, said coming up with numerical Philly jokes was surprisingly difficult. It took about two hours to generate a full list, Powley said, and she had to bounce ideas off other longtime Philadelphians, like Lee Metzger, who runs the offbeat sports apparel brand Philly Shirt Shop.

The content creator has also been overwhelmed by the positive response her videos have gotten, with commenters chiming in about the accuracy of Philly math.

“Yes, yes, yes! Tell them sister,” one TikTok user commented. “No lies were told,” wrote another followed by a trio of Eagle emojis.

“I love the reactions,” Powley said. “Putting anything out in Philly is kind of nerve-racking because if Philadelphians don’t like something, they’re going to tell you.”

Powley plans to continue her Philly math lessons on TikTok “for as long as people are enjoying them,” growing more inspired by the suggestions other presumed Philadelphians are leaving in the comments.

Her favorites? That Philly math is adding 10 to 15 minutes to the bus schedule, Powley said, or involves measuring distance in the minutes it takes to get there in traffic — not miles — when someone asks how far away something is.

There are, of course, Philly customs that can’t be quantified, Powley said, like crying equally hard when our sports teams win or lose.

“I love our pretzels,” Powley said. “And I love our city.”