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Kalcufy

Drywall Calculator

What Is Drywall?

Drywall (also called sheetrock, gypsum board, or plasterboard) is a construction material made of gypsum plaster (calcium sulfate dihydrate, CaSO₄·2H₂O) pressed between two thick sheets of paper. It is the most common interior wall and ceiling material used in North America, having largely replaced traditional lath and plaster since the 1950s. Drywall comes in standard 4-foot-wide panels of varying lengths (8, 10, and 12 feet) and thicknesses (¼", ⅜", ½", and ⅝"). The gypsum core provides fire resistance because when exposed to heat, the water molecules in the gypsum evaporate, slowing the spread of fire. Specialized types include moisture-resistant (green board) for bathrooms and kitchens, fire-rated (Type X) with glass fibers for garages and shared walls, and soundproof varieties with damping compounds for noise reduction between rooms.

How the Drywall Calculator Works

This calculator estimates drywall materials by computing the total wall area (perimeter × height), optionally adding ceiling area (length × width), then subtracting openings for doors and windows. A waste factor (typically 10-15%) is added to account for cuts around outlets, corners, and fitting. The total area is divided by the chosen panel size to determine sheets needed, always rounding up since partial sheets cannot be purchased. From the sheet count, the calculator derives fastener requirements (~32 screws per 4'×8' sheet), joint compound quantity (~1 gallon per 100 sq ft for 3 coats), and tape length based on joint linear footage. Cost estimation multiplies sheet count by your price per sheet and adds optional labor costs, giving you a complete project budget before you visit the hardware store.

Frequently Asked Questions

How many sheets of drywall do I need for a 12×12 room?

A 12' × 12' room with 8-foot ceilings, 1 door, and 2 windows needs approximately 17 sheets of standard 4'×8' drywall (including ceiling and 10% waste). Without the ceiling, you'd need about 12 sheets. The exact count depends on your waste factor, number of openings, and panel size chosen.

What type of drywall should I use in a bathroom?

Use moisture-resistant drywall (green board) for bathroom walls and ceilings that are not directly in the shower or tub area. For shower enclosures and tub surrounds, use cement backer board (like Durock or HardieBacker) instead — green board is water-resistant but NOT waterproof and will fail in direct wet areas.

How many drywall screws do I need per sheet?

Plan for approximately 32 screws per 4'×8' sheet (about 1 screw per square foot). Screws should be placed every 12 inches along edges and every 16 inches in the field (center area). For ceilings, you may need slightly more screws — approximately 36 per sheet — because they fight gravity.

What is the difference between Type X and regular drywall?

Type X (fire-rated) drywall contains glass fibers in its gypsum core that hold the board together longer during a fire. A ⅝" Type X sheet provides a 1-hour fire rating, while regular ½" drywall provides about 30 minutes. Building codes require Type X in attached garages, between dwelling units, and in furnace/mechanical rooms.

How much joint compound and tape do I need?

Plan for approximately 1 gallon (3.78 L) of pre-mixed joint compound per 100 square feet of drywall for a 3-coat finish (tape, fill, and skim). A standard 5-gallon bucket covers about 460 sq ft. For tape, one 500-foot roll covers approximately 460 sq ft of installed drywall.

Should I hang drywall vertically or horizontally?

Horizontally is preferred for most residential walls because it reduces the total length of joints to tape and creates a stronger wall. The long horizontal edge (tapered) creates flush joints that are easier to finish. Vertical installation is better for rooms with ceilings over 9 feet or for commercial applications with metal studs.

How much does it cost to drywall a room?

Material costs run $0.40-$0.65 per square foot for standard drywall (about $12-$20 per sheet). Professional installation including hanging, taping, and finishing costs $1.50-$3.00 per square foot. A typical 12×12 bedroom with ceiling costs $350-$600 for materials and $750-$1,500 for professional installation.

What thickness drywall should I use?

Use ½" for standard walls with studs at 16" on center (most common). Use ⅝" for ceilings (prevents sagging), fire-rated assemblies, and walls with studs at 24" on center. Use ¼" for curved walls and repairs over existing surfaces. Use ⅜" for minor re-covering of existing walls.