# Drywall and plasterboard calculator

> Drywall sheets for a room's walls and ceiling after doors and windows, with screws, joint tape and compound, for 4 × 8 ft or metric plasterboard.

Interactive version: https://www.calcopenly.com/construction/drywall-calculator
Subject: Construction and home calculators

Board area is the wall area, 2 × (length + width) × height, plus the ceiling if included, minus doors and windows. Sheets to buy are that area plus waste divided by the area of one sheet, rounded up. Screws, tape and joint compound scale with board area at the rates used here: one screw, 0.37 ft of paper tape and 0.009 US gal of all-purpose compound per square foot.

The default 14 × 12 ft room with 8 ft walls, a ceiling and 36 ft² of openings has 548 ft² of board. With 10% waste that is 19 sheets of 4 × 8 ft, about 548 screws, 203 ft of tape and 4.9 gal of compound, or two 4.5 gal pails.

Metric sheets such as 1200 × 2400 mm are converted exactly, so results match in either unit. The drawing shows where sheet joints fall on each wall; it does not plan cuts, which is what the waste allowance covers.

## Inputs

- **Room length**
- **Room width**
- **Wall height**
- **Include the ceiling**
- **Doors and windows (total area)**: About 21 ft² per door and 15 ft² per window.
- **Sheet size** (options: 4 × 8 ft, 4 × 10 ft, 4 × 12 ft, 1200 × 2400 mm, 1200 × 2700 mm, 900 × 1800 mm)
- **Waste allowance**: 10% covers cut-offs around openings; use 15% for rooms with many corners.

## Results

- Sheets to buy (sheets) — main result
- Board area (ft²)
- Board area (m²)
- Screws (screws)
- Joint tape (ft)
- Joint tape (m)
- Joint compound (US gal)
- Joint compound (L)
- 4.5 gal pails of compound (pails)

## Formula

$$
N = \left\lceil \frac{\big(2(\ell + w)h + \ell w - A_{\text{open}}\big)(1 + \text{waste})}{A_{\text{sheet}}} \right\rceil
$$

## Worked examples

### 14 × 12 ft room, 8 ft walls and ceiling, 4 × 8 sheets

- Room length: 14 ft
- Room width: 12 ft
- Wall height: 8 ft
- Doors and windows (total area): 36 ft²
- Sheet size: 4 × 8 ft
- Waste allowance: 10%
- **Board area: 548 ft²**
- **Sheets to buy: 19 sheets**
- **Screws: 548 screws**
- **Joint tape: 202.8 ft**
- **Joint compound: 4.93 US gal**
- **4.5 gal pails of compound: 2 pails**
- Checked against: Python decimal: 2(14 + 12) × 8 + 168 − 36 = 548 ft²; × 1.1 ÷ 32 = 18.84 → 19; tape 0.37 × 548 (USG); compound 9 gal per 1,000 ft² (USG)

### Metric 4 × 3 m room, 2.4 m walls only, 1200 × 2400 sheets

- Room length: 4 m
- Room width: 3 m
- Wall height: 2.4 m
- Include the ceiling: no
- Doors and windows (total area): 0 ft²
- Sheet size: 1200 × 2400 mm
- Waste allowance: 0%
- **Board area: 33.6 m²**
- **Sheets to buy: 12 sheets**
- Checked against: Hand calculation: 2(4 + 3) × 2.4 = 33.6 m² ÷ 2.88 m² per sheet = 11.67 → 12

### Edge: 8 ft cube walls fit whole sheets exactly

- Room length: 8 ft
- Room width: 8 ft
- Wall height: 8 ft
- Include the ceiling: no
- Doors and windows (total area): 0 ft²
- Sheet size: 4 × 8 ft
- Waste allowance: 0%
- **Board area: 256 ft²**
- **Sheets to buy: 8 sheets**
- **4.5 gal pails of compound: 1 pail**
- Checked against: Hand calculation: 4 walls × 64 ft² = 256 ft² = 8 sheets of 32 ft² with no remainder

## Questions

### How many sheets of drywall do I need?

Add the walls, 2 × (length + width) × height, and the ceiling, subtract doors and windows, add waste and divide by the sheet area. A 14 × 12 ft room with 8 ft walls has 416 ft² of wall and 168 ft² of ceiling; less 36 ft² of openings that is 548 ft². With 10% waste it needs 18.8 sheets of 4 × 8 ft (32 ft²), so buy 19.

### How many sheets of drywall for a 12 × 12 room?

19 sheets of 4 × 8 ft for walls and ceiling at 8 ft high, with 10% waste and no openings deducted. The walls are 2 × (12 + 12) × 8 = 384 ft² and the ceiling 144 ft², 528 ft² in all, or 16.5 sheets before waste. With 4 × 12 ft sheets (48 ft²) the same room needs 13.

### What drywall is required between a garage and a house?

At least ½ in gypsum board on the garage side of the wall separating the garage from the house, and 5/8 in Type X gypsum board where the garage has habitable rooms above it (2021 IRC Table R302.6). Sheet thickness does not change the sheet count here; order the thickness the code or your plans call for.

### How much joint compound and tape do I need for drywall?

This calculator allows 370 ft of paper tape and 9 US gal of all-purpose compound per 1,000 ft² of board, which is 0.37 ft and 0.009 gal per square foot. For 548 ft² that comes to 203 ft of tape and 4.9 gal of compound, two 4.5 gal pails. Coverage differs between compound types, so compare with the figure on the pail.

### How accurate is the drywall and plasterboard calculator?

Accuracy depends on your inputs and the method's assumptions. Decimal arithmetic uses 50 significant digits, but estimates, numerical methods and source data can be less precise; the displayed rounding does not remove those limits. It is checked against 3 worked examples whose answers come from independent sources; for example, “14 × 12 ft room, 8 ft walls and ceiling, 4 × 8 sheets” is checked against Python decimal: 2(14 + 12) × 8 + 168 − 36 = 548 ft²; × 1.1 ÷ 32 = 18.84 → 19; tape 0.37 × 548 (USG); compound 9 gal per 1,000 ft² (USG).

### Where does the method come from?

USG Sheetrock paper joint tape — coverage about 370 ft per 1,000 ft² of board; USG Sheetrock UltraLightweight joint compound — about two 4.5 gal pails per 1,000 ft²; USG Gypsum Construction Handbook — screw spacing 12 in on ceilings, 16 in on walls; International Code Council — 2021 IRC Table R302.6: garage separation, ½ in gypsum board on the garage side, 5/8 in Type X under habitable rooms.

## Sources

- [USG Sheetrock paper joint tape — coverage about 370 ft per 1,000 ft² of board](https://www.usg.com/api/download-center/v1/assets/f6d373bc-3db0-5da7-9c1e-88bad68531cb?download=true&country=us)
- [USG Sheetrock UltraLightweight joint compound — about two 4.5 gal pails per 1,000 ft²](https://assemblies-tools.usg.com/content/usgcom/en/products/walls/drywall/joint-compound/ultralightweight-joint-compounds/sheetrock-ultralightweight-joint-compound.html)
- USG Gypsum Construction Handbook — screw spacing 12 in on ceilings, 16 in on walls
- International Code Council — 2021 IRC Table R302.6: garage separation, ½ in gypsum board on the garage side, 5/8 in Type X under habitable rooms