Use string and stakes or batterboards to lay out lines representing the deck and measure off those to locate the footing positions.

To get started, use a plumb bob to transfer the outside edges of the deck from the ledger board down to ground level.

Nail string to the siding and tie the other ends to wood batterboards or stakes set out beyond the length of the deck.

Use the 3-4-5 method to set the strings square (at a 90 degree angle) to the house.

Mark a point on the string 3 feet (36") from where the string hits the wall.

Mark a 2nd point on the house wall 4 feet (48") from where the string hits the wall.

Measure out from the 1st point on the wall to the 2nd point on the string and move the string till the 2nd point is exactly 5 feet (60") from the 1st point on the house wall. Then the string is square to the house.

Marking Footing Positions on Strings and on Ground

Measure and mark the length of the deck on each string.

Tie a third string between those marks to represent the outside edge of the deck. Using the plan as a reference, measure and mark the center of each footing position on the strings.

Line up a plumb bob with each mark on the string. Drop the plumb bob to transfer those marks to ground level. Mark each spot with a nail and a bright strip of tape or cloth.