Free Drywall Calculator — Sheets, Tape & Compound

How to Use the Drywall Calculator

How to Calculate Drywall for a Room

Drywall estimation follows a straightforward formula: Total Area ÷ Sheet Area × (1 + Waste Factor). Measure all the wall surfaces you plan to cover, add the ceiling area if applicable, subtract the area of doors and windows, then divide by the area of your chosen sheet size. A standard 4' × 8' sheet covers 32 square feet. For example, a 12' × 12' room with 8' ceilings has four walls totaling 384 square feet. Subtract one door (20 sq ft) and two windows (24 sq ft) to get 340 square feet of wall area. Divide by 32 to get 10.6 sheets, then multiply by 1.10 for a 10% waste factor — you need approximately 12 sheets of 4' × 8' drywall.

This calculator handles the math automatically. Enter your room dimensions or total area, count your doors and windows, choose a sheet size, and the calculator returns the exact number of sheets along with the joint compound, tape, and screws you need to finish the job.

Choosing the Right Sheet Size

Drywall sheets come in three common lengths, all 4 feet wide. Your choice depends on ceiling height, handling capacity, and the number of seams you want to minimize. 4' × 8' sheets (32 sq ft each) are the standard for residential work. They are light enough for one person to carry and maneuver, fit through standard doorways, and work perfectly for rooms with 8' ceilings when hung horizontally. 4' × 10' sheets (40 sq ft each) are ideal for 9' ceilings — a single horizontal sheet reaches from floor to ceiling with minimal cutting. They produce fewer horizontal seams than 4' × 8' sheets on taller walls, but they are heavier and harder to handle solo. 4' × 12' sheets (48 sq ft each) are the professional choice for 8' walls because a single sheet spans the full wall width in many rooms, eliminating vertical butt joints entirely. However, they require two people to carry and install, and not all home centers stock them — you may need to order from a drywall supply house.

Room Mode vs Area Mode

This calculator offers two input modes for different scenarios. Room mode is designed for standard rectangular rooms — enter the room length, width, and wall height, and the calculator computes the total wall perimeter and area automatically. It also lets you specify the number of doors and windows to subtract from the total, and optionally includes the ceiling area. Room mode is the fastest path for bedrooms, offices, and other four-wall spaces.

Area mode is for non-rectangular situations: basement finishing with irregular walls, garage conversions, additions with angled walls, or any project where you already know the total square footage. Enter the total area directly and the calculator skips the room geometry step. Use area mode when you have already measured each wall segment individually or when the space does not fit a simple rectangle.

Accounting for Doors, Windows, and Openings

Every door and window reduces the drywall area, but the savings are smaller than most people expect. Standard deductions are 20 square feet per door (a 3'-0" × 6'-8" interior door) and 12 square feet per window (a typical 3' × 4' double-hung). These conservative estimates account for the fact that you still need drywall strips above doors and below windows, and the cutout pieces from those openings are rarely reusable in other locations.

For small openings like electrical panels, medicine cabinets, or HVAC registers, do not deduct them from the total area. You will cut the drywall to fit around these items on site, and the cutout waste is included in your waste factor. Only deduct full-size doors and windows. For oversized openings like sliding glass doors or pass-throughs, switch to area mode and measure the actual wall surface directly.

Estimating Joint Compound, Tape, and Screws

Hanging drywall is only half the job — taping and finishing the seams is where the real work begins. The rules of thumb for materials are well established: joint compound requires approximately 1 gallon (or about 4.5 pounds of premixed compound) per 14–15 sheets of 4' × 8' drywall, which works out to roughly 1 gallon per 100 square feet of drywall area. This covers three coats — taping coat, fill coat, and finish coat — plus inside corner beads. Paper tape usage runs about 12 linear feet per sheet, covering all horizontal and vertical seams plus inside corners. A standard 250-foot roll handles approximately 20 sheets. Drywall screws require about 28 per 4' × 8' sheet when fastening to studs at 16" on center. The standard screw pattern is 12" on center along edges and 16" on center in the field (interior studs). A pound of 1-5/8" drywall screws contains roughly 180 screws — enough for about 6 sheets.

Pro Tips for Drywall Estimation

• Order 10% extra drywall beyond your calculated need. Sheets get damaged in transport, cuts go wrong, and corners never line up perfectly. Having spare sheets on site is far cheaper than making a second delivery trip or delaying the taping crew.
• Hang ceilings first, then walls. Ceiling sheets rest on the wall sheets' top edge, creating a tighter joint. This sequence also means wall sheets support the ceiling edges, reducing the need for extra fasteners or adhesive overhead.
• Use the longest sheets practical to reduce the number of seams. Fewer seams means less taping, less compound, and a smoother finished surface. A single 4' × 12' sheet hung horizontally on an 8' wall eliminates every vertical butt joint for that span.
• Check local delivery options for 10' and 12' sheets before committing to 4' × 8'. Many drywall suppliers offer free or low-cost delivery and will even boom the sheets through a second-story window, saving you the labor of carrying them up stairs.
• Use moisture-resistant drywall (green board) for bathrooms, laundry rooms, and kitchens, and mold-resistant (purple board) for basements or any area prone to humidity. These specialty sheets cost more per unit but prevent costly mold remediation and replacements down the road.