The answer depends on the size and shape of your deck, the size of your footings, and the size of your beams. The larger the beam and footing size the fewer footings that are required. For most situations you will want to place footings and posts less than 8' apart. If you are planning on installing a hot tub or porch on top of your deck you will usually need more footings and posts to support the additional loads. Free standing decks that are not attached to the house with a ledger board will require an additional beam and row of footings. Decks with lots of angles may also require additional footings. Use the decks.com footing and beam calculator to test your design.