How to calculate drywall
Add up the area you're covering, then divide by the sheet size and round up:
Sheets = (Wall area + ceiling) × (1 + waste %) ÷ sheet area
Wall area is the perimeter times the height: 2 × (length + width) × height. A 12 × 12 room with 8-ft walls is 384 sq ft of wall, plus a 144 sq ft ceiling — 528 sq ft. With 4 × 8 sheets and 10% waste, that's about 19 sheets.
Choosing a sheet size
- 4 × 8 ft: the standard — easy to carry and lift.
- 4 × 10 / 4 × 12 ft: fewer seams to tape in big rooms, but heavy.
Don't forget the finishing materials
Beyond sheets you'll need screws, joint tape, and joint compound (mud). A rough rule is about half a pound of compound per square foot for taping and three coats — the calculator estimates this for you.
Frequently asked questions
How many drywall sheets do I need?
Find the total area to cover — the walls (room perimeter × ceiling height) plus the ceiling if you are drywalling it — then divide by the area of one sheet and round up. A 12 × 12 room with 8-ft walls plus ceiling is about 528 sq ft; with 4 × 8 sheets (32 sq ft) and 10% waste, that is roughly 19 sheets.
What size drywall sheets should I use?
4 × 8-foot sheets are the standard and easiest to handle. Longer 4 × 10 and 4 × 12 sheets cover more area with fewer joints to tape and finish, which speeds up large rooms — but they are heavier and harder to maneuver. Pick the size that fits your space and helper situation.
Should I subtract doors and windows?
For ordering, most people do not — you cut drywall around openings and the offcuts rarely fill another spot cleanly. Counting the full wall area, plus a waste allowance, conveniently builds in a buffer. This calculator counts full walls.
How much joint compound and tape do I need?
As a rough guide, plan on about 0.5 lb of joint compound per square foot of drywall for taping and three coats, and roughly 40 feet of tape per 100 square feet. Buy a little extra — running out mid-coat means waiting for it to dry before you can continue.
Disclaimer: Results are estimates for planning and count full walls without subtracting openings. Confirm quantities for complex layouts and high or vaulted ceilings.