When it’s 7-Eleven’s birthday, it’s everyone’s birthday. So get ready to party!

All 7-Eleven locations in the city invite New Yorkers to celebrate the franchise’s 85th birthday Wednesday with free 7.11-ounce Slurpees from 11 a.m. to 7 p.m.

Since 2002, the convenience store chain has celebrated its birthday by giving out free Slurpees. Nationwide, an estimated 7 million Slurpees will be given away tomorrow, according to 7-Eleven’s website.

So how do the convenient stores prepare for the long lines and anxious customers?

Each store orders three additional Slurpee barrels and at least 1,000 additional cups for the day, totaling 7 million cups nationwide, said Laura Gordon, vice president of brand innovation for 7-Eleven.

The franchise also adds extra staffers employees in order to help with the influx of customers.

Employees at the 7-11 on 8th Avenue in Midtown said they’re gearing up for lines that stretch around the block.

“We are changing it up this year, though, so that the staff makes the Slurpees and hands them to customers rather than customers making the Slurpees themselves,” Raj Gopal, manager of the 7-Eleven on 8th Ave., said.

The 7-Eleven on 8th Ave. will serve nine flavors including watermelon lime, Mountain Dew, sugar-free strawberry banana, lemon crème, white cherry, Dr. Pepper, Coca-Cola, raspberry and Pina Colada.

7-Eleven has 30 new locations scheduled to open in the city this year, and plans to grow to 135 stores by 2017. While other city business owners may grumble that 7-Eleven is undercutting them, today may just hit New Yorkers’ sweet spot. From a marketing and branding perspective, many companies benefit when they give their customers giveaways, said one PR expert.

“Everyone likes free stuff,” a public relations professional told Metro. “Those unfamiliar with the store or not interested in 7-Eleven may give it a shot because it’s a free drink on a hot summer day, and once they are inside they may see that 7-Eleven sells items they’re actually interested in.”

Other freebies

1. July 13th is Cow Appreciation Day at all Chick-fil-A restaurants. If you wear a partial cow costume, you get a free entrée. If you dress like a cow from “head-to-hoof,” you get a free meal.

2. Rita’s Ice gives away a free, regular size Italian Ice to each and every guest to mark the first day of Spring.

3. On Friday, July 13th from noon to 3:00 p.m., you’ll be able to get a free tall Starbucks Refreshers beverage.

4. On National Doughnut Day, Dunkin’ Donuts and Krispy Kreme give away free doughnuts to all customers.

5. On Free Cone Day at Ben and Jerry’s, the company offers a free scoop of frozen yogurt, ice cream or sorbet in a cone.

6. On National Pi Day, March 14, Whole Foods Market gives out a free slice of pie to all customers.

7. On National Pancake Day, February 28, IHOP gives out a free stack of buttermilk pancakes to its customers.

8. On National Coffee Day, Krispy Kreme and 7-Eleven give out free cups of coffee.

9. For National Frozen Yogurt Day, head on over to Yogurtland for a free frozen yogurt.

10. On National Ice Cream Day, enjoy a free ice cream at your neighborhood Baskin Robins.

Where to slurp up

Here are eight 7-Eleven locations in Manhattan:

247 3rd Avenue

535 8th Avenue

1453 3rd Avenue

103 West 14th Street

171 Madison Avenue

395 3rd Avenue

675 Amsterdam Avenue

1594 York Avenue

View 7-11 Day Slurpees in Manhattan in a larger map