Joint compound calculator

How this calculator works

It works out the board area of the room (four walls less doors and windows, plus the ceiling if you include it) and multiplies it by how much compound a square foot of board takes for a tape coat and two finish coats. A waste allowance is added and the total is rounded up to whole buckets.

The default rate, about 10 gallons of ready-mixed all-purpose compound per 1,000 sq ft of board, is the common published figure for a standard finish. Paper tape runs about 370 ft per 1,000 sq ft.

Worked example

A 14′ × 12′ room with 8′ walls, one door, two windows and the ceiling has 365 + 168 = 533 sq ft of board. At 10 gallons per 1,000 sq ft that is 5.33 gallons; with 10% waste it is 5.86 gallons, which the list buys as 2 buckets of 4.5 gallons. It also needs about 197 ft of tape, so 1 roll of 500 ft.

Tips before you buy

• Use a setting-type (powder) compound for the tape coat on large jobs; it hardens faster and shrinks less. Finish with ready-mixed.
• Lightweight ready-mixed compound is easier to carry and sand; coverage differs between products, so check the bucket and adjust the rate.
• Keep the lid on and a thin layer of water over the mud between coats so it does not skin over.
• Count outside corners on soffits, window returns and wall ends, not just the room corners.

Questions

How much joint compound do I need per sheet of drywall?

At about 10 gallons per 1,000 sq ft, a 4×8 sheet takes roughly a third of a gallon for a tape coat and two finish coats. A 4.5-gallon bucket finishes about 14 sheets.

What is the difference between all-purpose and topping compound?

All-purpose compound works for every coat, including bedding the tape. Topping compound is lighter and smoother for the final coats but does not hold tape as well. Most small jobs use all-purpose throughout.

Do I need extra compound for a smooth Level 5 finish?

Yes. A Level 5 finish adds a thin skim coat over the whole surface, so it takes noticeably more compound than the three-coat rate used here. Raise the compound-per-area figure under Coverage and waste if you plan to skim.