Keyboards do not feature a dedicated key that lets you insert the Pi (π) symbol when typing equations in Word 2013 and Word 365. You can, however, use either a universal key combination or Word 2013's Equation function to add Pi symbols to your document. Further, Word 2013 lets you bind the Pi symbol to any keyboard shortcut of your choice.
Universal "Pi" Key Combination
Place your cursor at the location where you want the Pi symbol to appear. Hold down the Alt key, and then type 2-2-7 on the Num pad. The Pi symbol appears once you release the Alt key. If the Pi symbol doesn't appear, press the Num Lock key, and then try again.
Pi Symbol as Font
Open the Home tab, and then select Symbol from the pull-down menu on the Font group. Next, place the cursor in any preferred location within the document, and then press the P key. The Pi symbol (π) appears instead of the letter P.
Pi Symbol as Equation
Click the Insert tab.
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Click Equation on the Symbols group.
Use the arrow-shaped keys on the Symbols group to cycle through available symbols, and then click π to insert the Pi symbol.
Create Pi Symbol Shortcut
Click the Insert tab, click Symbol on the Symbols group, and then click More Symbols.
Select your preferred font style, such as Arial or Calibri, from the Fonts pull-down menu. Select the Pi symbol -- certain fonts may have more than one type of Pi symbol -- and then click Shortcut Key.
Place your cursor within the Press New Shortcut Key field, press the key that you want to include within the shortcut (for example, Ctrl-R), and then click Assign.
Click Close to exit the Customize Keyboard dialog box.