• Drywall finishing tools may be part of the estimate.drywall tools image by Sherri Camp from Fotolia.com
  
  Estimating drywall work is an exercise in paying attention to details. The first of these details is assessing the quality of the surfaces where you will attach and finish the drywall. Out-of-square spaces and items out-of-plumb and -level increase the time and materials you'll need to finish drywall installations to an acceptable level of quality.
  
  

Information-Gathering

• Check for plumb and level. The plumb bubble on a 4-foot level should be close to the center when checking walls, and the level bubble should be at the center when checking ceilings. If ceilings and walls are not plumb and level you will need to estimate the cost and installation time for furring strips to bring them into level. Take precise measurements so you don't run short of material or over order. Measure the length, width and height of rooms at the walls.
  
  Call or visit the store where you'll buy your materials to learn the cost of drywall, drywall tape and drywall compound.
  
  

Calculations

• Multiply the length times the height of each wall to get their area in square feet. Add together the square footage of all walls. Multiply the length times the width of each ceiling, and add those square footages together. Add the wall square footage to the ceiling square footage to arrive at the total square feet of drywall needed. The biggest and most unpredictable expense in hanging and finishing drywall is labor. Do not deduct the square footage of windows and doors from your calculations. Any pieces left over once you've cut around the openings will not have the beveled edge provided by the factory, and using them in piecework fashion is more expensive than considering them as waste.
  
  Divide your total square footage by 32 if you will use 4-foot by 8-foot sheets, or by 48 if using 4-foot by 12-foot sheets. The result is the number of sheets you need. Multiply that number by 15 percent, and add the result to your total number of sheets to account for waste, rounding up to the next sheet.
  
  Add 2 gallons of joint compound and 180 feet of wallboard tape for each 300 square feet of drywall. Figure 3 pounds of screws for every 500 square feet of drywall.
  
  

Considerations

• In addition to including furring strips and fasteners, if the walls or ceilings are not level and plumb, you should consider other costs such as corner trim, tools and additional labor. Use corner trim on outside corners (those that protrude into the space). Corner trim comes in rolls, for locations where you do not expect the corners to take many bumps, or in rigid strips of metal for the most secure corners. You need drywall knives in at least three different widths, trays to hold the compound while applying it, sponges and sanding supplies. Drywall is heavy, so you will need at least one helper. Figure the cost of additional labor based on the prevailing wages for that kind of work in your area.