Pi Day occurs on March 14, because the date is written as 3.14 in the United States. Pi is the ratio of the circumference of a circle to its diameter, or approximately 3.14 (its exact value is infinite and can't be calculated). March 14 also happens to be Albert Einstein's birthday.
RELATED: What is Pi Day? What to know about the holiday to celebrate math's beloved irrational number
With eating out becoming more of a luxury, restaurants use such deals to help draw customers to fast casual and fast food chains.
Pi Day has also become synonymous with pizza pie (and other round foods) - here are some deals to round out your celebration.
Pizza Hut
From March 12-14, Pizza Hut has been offering a free large one-topping pizza with purchase of a large menu-priced pizza.
7-Eleven
Loyalty members can get any flavor large pizza for $3.14 in 7-Eleven, Speedway and Stripes stores - limited to one transaction, two per day.
BJ's Restaurant & Brewhouse
Dine-in customers at BJ's Restaurant & Brewhouse can get a mini one-topping pizza for $3.14.
Blaze Pizza
Build-your-own-pizza chain Blaze is offering an 11-inch pizza for $3.14 in-store at participating locations.
Burger King
As part of its week of breakfast deals, Burger King is offering a free Hershey's sundae pie with a $3.14 purchase.
California Pizza Kitchen
CPK rewards members can get an Original BBQ chicken, pepperoni, or traditional cheese pizza for $3.14 with a dine-in purchase of $25.
Taco Bell
Get a Taco Bell Mexican Pizza for just $3.14.
(The-CNN-Wire & 2023 Cable News Network, Inc., a Time Warner Company. All rights reserved.)