I’m a style expert — this measuring trick confirms if you should have long or short hair

This hairstyle hack really bangs.

A style influencer has passed along a nearly surefire, geometric tactic to tell if you’re better suited with short or long hair.

“This viral hack has helped me decide to grow my hair again, so sharing for those that are between two minds about cutting or growing their hair,” South African beauty expert Laudi Lee posted to her nearly 375,000 Instagram followers.

It requires two pens and a measuring tape to do, and you begin by holding one pen vertically from the earlobe level down.

Next, take the second pen and place it horizontally beneath your chin so that the two form a right angle as they meet.

Use the horizontal pen to leave a little mark on the other writing implement, and then break out the measuring tape to see where it notches up.

“If it’s less than 2½ inches, you look better with short hair,” Lee says. If it’s more than 2½ inches, you look better with long hair.”

While Lee — who found herself to be better with long hair — admits the pen hack isn’t a hair-lock for success, she described it as “a nice little trick to help you decide.”

“Mine measures 3 inches so that would mean long hair and I agree,” one user on Instagram commented.

“I absolutely love this! A bit late though as I’ve just cut mine,” joked another.

“Wow. I needed this,” a third added.

If your haircut is of the under-2½-inch variety, the suddenly resurging “pageboy cut” may be your savior.

The hysterically dated cut — prominent bangs and all — is seeing a comeback with variations on “bobmania” being pushed by celebrities including Hailey Bieber, Jenna Ortega, Kim Kardashian, Katie Holmes and Mindy Kaling.