Results update as you type. Round up when ordering.
Based on standard 4×8 / 4×12 ft panels and ready-mix all-purpose joint compound (e.g. USG Sheetrock) at ~10 gal per 1,000 sq ft. Check the label.
Formula checked against manufacturer specs
Rounded up to whole units
Runs in your browser
How to estimate drywall
Add wall area (perimeter × height) to ceiling area (length × width). Don't subtract small doors and windows—offcuts rarely fit elsewhere, and the extra covers breakage. Divide by sheet area: 32 sq ft for 4×8, 48 sq ft for 4×12.
Example: a 12 × 12 ft room with 8 ft walls: 48 × 8 = 384 + 144 ceiling = 528 sq ft. With 10% waste, 580.8 sq ft ÷ 32 = 18.2 → 19 sheets of 4×8.
Which thickness?
1/2 in: standard for interior walls on studs 16 in on center
5/8 in (Type X): ceilings with 24 in joists, garages adjoining living space, and fire-rated assemblies where code requires it
Moisture-resistant board for bathrooms (not as a tile backer in showers—use cement board there)
Finishing materials
Plan on roughly 10 gallons of ready-mix all-purpose joint compound per 1,000 sq ft of board for taping and three coats (USG's published coverage is about 9.4–10 gal per 1,000 sq ft; one 4.5 gal pail finishes roughly 450 sq ft). A Level 5 skim coat roughly doubles that and about one drywall screw per square foot. Longer 12 ft sheets mean fewer butt joints and less taping.
It uses the standard formula shown on this page and rounds bags, boxes and pieces up to whole units. Product sizes vary by brand, so confirm with the label or your supplier before you buy.
Should I buy extra material?
Yes. A 5–10% allowance covers cuts, spills and uneven surfaces; running short mid-job usually costs more than a few leftovers.
Is this calculator free?
Yes. Every PorchMath calculator is free, needs no account and runs entirely in your browser.