Ceiling Grid Calculator Enter the total square footage of the room Enter the combined length of all walls in room in feet Approximate estimate of materials needed: pieces of 12 foot main runners. pieces of 4 foot cross-tees. pieces of 2 foot cross-tees. (If your ceiling tile is 2' x 2') pieces of 12 foot wall mold; Notes: Use 4 pieces of ceiling wire per main runner, spaced evenly. Length of hanger wire will be distance from ceiling to anchor point plus 2 feet extra to allow room to adjust and tie.