We celebrate **Pi Day** each year on March 14, because 3.14 are the first digits in Pi. Pi is a mathematical constant that represents the ratio of a circle's circumference to its diameter. Pi is actually an irrational number, meaning it is an unending, patternless decimal.

Pi is often shown as the Greek letter π. The symbol is used to make fun "pie" puns and jokes, especially in memes and, of course, on novelty t-shirts. Here are some fun Pi t-shirts that would be a great choice to wear on Pi day or any time you want to share your geeky math love.

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This is a great text Pi Day t-shirt with a funny slogan for math nerds. The full slogan reads "They Call Me PI Because I'm Irrational and I Don't Know When To Stop". The arrangement of the different mashup fonts is fun and playful. The white text pops against the black t-shirt (also available in other dark colors).

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This is a patriotic Pi Day t-shirt design for math geeks. The first digits of PI are arranged in circles around the Greek letter. The red, white, and blue colors are arranged in the familiar style of Captain America's famous shield.

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Pi is to Pie what π is to a cartoon image of a pie. This funny graphic Pi shirt takes the play on words and adds in pie humor. This funny t-shirt is available in sizes Small to 3XL.

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Here the word PI, represented by the Greek letter π, helps spell out the name of a bird: the Magpie (or MagPI). The cute stylized name is accompanied by a cartoon image of a Magpie bird. This is a fun cartoon Pi Day t-shirt for math geeks who are also bird lovers!

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If the math symbol Greek letter π makes you hungry, this funny simple text Pi Day shirt is for you. A large blue π symbol is accompanied by smaller text above that readsy simply "Mmmm..." as in YUM! Pie!