Celebrate Pi Day March 14 with $3.14 pizza, free pie and more

It’s not irrational to find pizzas for $3.14 Thursday.

March 14 is Pi Day, an annual celebration of the mathematical constant π (pi), which is the ratio of a circle's circumference to its diameter. The trillion-digit ratio is rounded to 3.14.

Albert Einstein was born on Pi Day and last year noted astrophysicist Stephen Hawking died on the made-up holiday.

Pi Day, not to be confused with Pie Day held in January, is a day with deals on pizza, pastry and pot pies.

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Aside from calculating your savings, it's a day to have fun with math too, said Syracuse University mathematics professor Graham Leuschke. He said you can search for your birthday in the digits of π and can create a "pi-ku" similar to a haiku poem. 

PiDay.org, which calls itself the official site for Pi Day, has additional ideas for activities to celebrate the day.

What is Pi Day?:Everything you need to know about celebrating

Math fun:This Google employee set a record calculating Pi to 31.4 trillion digits

March freebies:Your monthly guide to food specials, meal deals and more

Pi Day pizza deals

Here are the deals available at participating locations Thursday unless otherwise noted. To be on the safe side, always check with your closest location before heading out. Also, some will require you to have a restaurant's app or be signed up for emails.

&Pizza: The company, which calls itself "an anti-establishment establishment," is holding weddings at four of its locations Thursday for selected couples and is offering a discount through Uber Eats Wednesday through Sunday. With promo code PIDAY19, get $3.14 off all &pizza and Uber Eats deliveries.

7-Eleven: With the 7Rewards app, get one slice of pizza for 50 cents. Or buy a whole pie in-store and get 314 7Rewards bonus points. With 7NOW, the convenience store chain's delivery service, get up to two whole pizzas for $3.14 each. 

Bertucci’s: Buy any large pizza and get a second pizza for $3.14 with code PIDAY. The chain says this deal “is available at all locations for lunch and dinner, and through all ordering platforms.”

BJ's Restaurant & Brewhouse: Get a mini one-topping pizza for $3.14 Thursday. Dine-in only. Learn more at www.bjsrestaurants.com/piday.

Blaze Pizza: The chain’s smartphone app is needed to get the $3.14 Pi Day deal Thursday on custom pizzas. One per order and in-restaurant only.

Cicis: Buy one adult buffet and large drink Thursday and get a second adult buffet for $3.14 with a coupon.

Domino’s: Not specific for Pi Day but through April 28, Domino’s is giving Piece of the Pie Rewards members an easy way to earn points that can redeemed for a free Domino's pizza – no matter what brand's pizza they buy. The latest version of Domino’s mobile app is needed to "to scan a pizza or an eligible image of a pizza.” Learn more at www.pointsforpies.com.

Fired Pie: From 2 p.m. to close Thursday, get any one-topping pizza for $3.14 with purchase of a drink. Limit one per person and not valid on third-party delivery services.

Fresh Brothers: Get any personal pizza for $3.14 Thursday for pick up, dine-in and delivery with promo code PIDAY on Thursday, March 14. Not valid with third-party services.

Hungry Howie's: Through Thursday, with the purchase of any Howie Bread at regular menu price, get a medium one-topping pizza for $3.14 with promo code 19PI. Carry out orders only. Florida locations are not participating in this promotion.

Jet's Pizza: Buy a large pizza at regular price Thursday and get a medium one-topping round pizza for $3.14 with code 314. While supplies last.

Mountain Mike’s Pizza: Get $5 off any Mountain-sized pizza with code 079984, or $3 off any large pizza Thursday with promo code 317445.

Pie Five Pizza: Get any 11-inch Signature Pizza for $3.14 Thursday. Limit one pizza per person and in-store only. No topping modifications allowed and there will be an additional charge for cauliflower crust, gluten-free crust and vegan cheese.

Pieology: Buy one Artisan Thin Pizza, get a second for $3.14 Thursday. Plus, Pie Life Rewards members making a purchase on Pi Day will get $2 off their next order. The chain also is holding the "Perfect Pieology Pull” cheese-pull contest. “Customers simply visit the nearest Pieology, roll up their sleeves, start pulling, and documenting their best efforts," the company said in a statement. "After submitting their photo or video posts on Instagram using the hashtag, #perfectpieologypull, the public will vote on the top five entries and the best ‘pull’ will be named champion and receive a $50 Pieology gift card.” Enter by midnight Thursday.

Pizza Inn: New and existing reward members get a Chocolate Chip Pizzert for $3.14 Thursday. The rewards app is available at www.pizzainn.com/rewards.

Rotolo’s Pizzeria: Get one-topping eight-inch pizzas for $3.14 Thursday for dine-in only at participating locations. Gulf Coast stores in Alabama are not included.

Slice: A mobile app that works with more than 10,000 pizzerias is offering $7 off pizza orders Thursday for new users with promo code LOCALPI7. This is for credit card orders and only on a user's first order with the app. “Minimum order total after deductions and promotions must be $15.50,” the offer's fine print states. Download the app at www.slicelife.com. 

Villa Italian Kitchen: Get full-size Neapolitan Cheese Pizzas for $3.14 Thursday with a coupon. Sign up for the coupon at www.villaitaliankitchen.com/piday.

Your Pie: The fast-casual pizza brand will have $3.14 pizzas at participating locations. In-store only, while supplies last. Additional pizzas or menu items may be purchased at full price. Stores also will offer games, bounce-back deals, prizes and giveaways throughout the day. Learn more at www.yourpie.com/pieday.

Other Pi Day deals

Bakers Square: Get $2 off any whole pie Wednesday or Thursday and double-crust fruit pies also will be baked with the pi symbol. Excludes cheesecake and carrot cake. Only valid when ordered in-restaurant and while supplies last.

Biggby Coffee: The Apple Pie Latte returns and is $3.14 Thursday.

Bojangles’: Get three Sweet Potato Pies for $3.14 Thursday while supplies last at participating locations. No coupon or app offer needed.

Boston Market: With a Pi Day coupon Thursday, get a free Rotisserie Chicken Pot Pie with the purchase of another pot pie and drink at any one of the more than 450 U.S. locations. The coupon is available at www.bostonmarket.com.

California Pizza Kitchen: Get a slice of Key Lime Pie for $3.14 Thursday.

California Tortilla: The fast-casual Mexican chain is celebrating St. Patrick’s Day Thursday. Get a free order of chips and queso with any purchase when you say “Pot o’ Gold” when placing your order. In-store only and cannot be combined with any other offer.

Cheddar’s Scratch Kitchen: Order the restaurant’s Homemade Chicken Pot Pie for dining in or to-go Thursday and get a free second pie to bake at home. No coupon needed, and Cheddar’s says it will provide the baking instructions. Learn more at www.cheddars.com/pieday.

Fresh Market: Get $3.14 off Old Fashioned Apple and Cherry Pies along with Chicken Pot Pies from the deli Thursday.

Kroger: Select pies are $3.14 for Pi Day including apple, cherry, peach and pumpkin pies.

Marie Callender's: Get a free slice of pie Thursday with purchase of a full-price adult menu and a coupon posted at www.mariecallenders.com/coupon-piday. Not valid with other promotions including Kids Eat Free, happy hour menu, lunch combos and daily dish specials.

Schlotzsky’s: The fast-casual chain is celebrating National Potato Chip Day Thursday. Get a free bag of potato chips with entrée purchase.

Starbucks: The coffee giant has one of its Happy Hour events on Pi Day. Starting at 3 p.m. Thursday, buy any grande or larger handcrafted espresso beverage or Frappuccino blended drink and get one free. This deal has been loaded on Starbucks Rewards members accounts. Non-members can sign up for the offer by creating an account at Starbucks.com. You can either add a Starbucks gift card to the account or choose an instant digital card when setting up the account.

Stop & Shop: All stores are selling eight-inch pumpkin, apple and Dutch apple pies for $3.14 Thursday.

White Castle: With a Pi Day coupon, get a Breakfast Slider combo for $3.14 Thursday. The combo includes a Breakfast Slider, hash brown and small coffee. The coupon is posted at www.whitecastle.com/pi-day.

Whole Foods Market: Large bakery pies are $3.14 off the regular price Thursday. Varieties vary by region.

More deals: Some local pizzerias, smaller chains and bakeries also will celebrate Pi Day with specials. Check social media accounts to find additional offers.

Follow USA TODAY reporter Kelly Tyko on Twitter: @KellyTyko