# Drywall Calculator

> Estimates the number of gypsum board sheets for walls (and optionally the ceiling) of a room with a waste allowance, plus screws at about one per square foot and joint compound at the USG rate of 10 gallons per 1,000 ft² of board.

- Calculator id: `drywall` · Category: Construction & Home (`construction`) · Tool name: `estimate_drywall_sheets`
- Canonical page: https://tttkmbb.com/construction/drywall · This document: https://tttkmbb.com/construction/drywall.md · JSON definition: https://tttkmbb.com/construction/drywall.json

## Purpose

Estimates the number of gypsum board sheets for walls (and optionally the ceiling) of a room with a waste allowance, plus screws at about one per square foot and joint compound at the USG rate of 10 gallons per 1,000 ft² of board.

**Use when:** You need to order plasterboard/drywall sheets, screws and joint compound for a room or a known wall area.

**Do not use when:** You need paint or wallpaper quantities for the finished wall (use paint or wallpaper), or metal-stud framing take-offs.

## Input

| Parameter | Type | Unit | Required | Description |
| --- | --- | --- | --- | --- |
| `unit_system` | enum: metric \| imperial |  | optional, default "metric" | Unit system of the length inputs (metric: m / cm / mm; imperial: ft / in). Outputs are reported in both systems. |
| `room_length` | number | m or ft | optional | Room length (m or ft); used with room_width and wall_height when wall_area is not given, and for the ceiling. (> 0, max 1000) |
| `room_width` | number | m or ft | optional | Room width (m or ft). (> 0, max 1000) |
| `wall_height` | number | m or ft | optional | Wall height (m or ft). (> 0, max 100) |
| `wall_area` | number | m² or ft² | optional | Total wall area to board (m² or ft²); replaces 2 × (length + width) × height when given. (> 0) |
| `include_ceiling` | boolean |  | optional, default false | Add the ceiling area (room_length × room_width). |
| `openings_area` | number | m² or ft² | optional, default 0 | Area of large openings (doors, windows) to deduct; small openings are usually not deducted because the cut-outs are waste. (min 0) |
| `sheet_size` | enum: 4x8_ft \| 4x12_ft \| 1200x2400_mm \| 1200x3000_mm |  | optional | Board size. Default 1200 × 2400 mm (metric) or 4 × 8 ft (imperial). |
| `waste_percent` | number | % | optional, default 10 | Extra material for cuts, breakage and offcuts, applied as a multiplier (1 + waste_percent/100). 10 % is typical for rooms with few openings; use 15 % for complex rooms. (min 0, max 50) |

## Output

| Field | Type | Unit | Description |
| --- | --- | --- | --- |
| `area_m2` | number | m² | Walls (+ ceiling) − openings. |
| `area_ft2` | number | ft² | Area in square feet. |
| `sheets_needed` | integer |  | ceil(area × (1 + waste_percent/100) / sheet_area). |
| `sheet_size_used` | string |  | Board size assumed. |
| `screws` | integer |  | About 1 screw per ft² of board (≈ 32 per 4 × 8 sheet at 16 in stud spacing). |
| `joint_compound_liters` | number | L | Ready-mixed all-purpose compound: 37.8 L per 100 m² of board (USG). |
| `joint_compound_gallons` | number | US gal | 10 gal per 1,000 ft² of board (USG). |
| `compound_pails_4_5_gal` | integer |  | ceil(gallons / 4.5), the common US pail size (about 17 L). |

## Formula

`area = 2 × (room_length + room_width) × wall_height (or wall_area) + room_length × room_width (if include_ceiling) − openings_area; sheets = ceil(area × (1 + waste/100) / sheet_area); screws ≈ area_ft² × 1; compound_gal = area_ft² / 100; pails = ceil(compound_gal / 4.5).`

Fastener spacing follows IRC R702.3.5 (screws at 16 in on walls and 12 in on ceilings with 16 in framing), which works out to roughly one screw per square foot. Compound coverage is USG's figure for taping and three-coat finishing of the joints.

## Data Sources

- USG – Sheetrock Brand All Purpose Joint Compound submittal sheet (≈ 10 gal per 1,000 sq ft of panels) — https://www.usg.com/content/dam/USG_Marketing_Communications/united_states/product_promotional_materials/finished_assets/sheetrock-all-purpose-joint-compound-submittal-J1969.pdf (reference, retrieved 2026-09-23)
- ICC – 2021 International Residential Code, Chapter 7 Wall Covering (R702.3.5 gypsum board fastening) — https://codes.iccsafe.org/content/IRC2021P2/chapter-7-wall-covering (standard, retrieved 2026-09-23)

Data freshness: `static`. Deterministic formula with fixed constants; results never go stale. Inputs supplied by the caller determine the output.

## API

- `GET https://tttkmbb.com/api/v1/calculate/drywall?`
- `POST https://tttkmbb.com/api/v1/calculate/drywall` with JSON body `{"inputs": {…}}`
- Response: unified envelope (`success`, `request`, `result.values`, `result.units`, `sources`, `freshness`, `timestamp`, `next_actions`, `links`); see https://tttkmbb.com/docs/response-format.md
- Schema: https://tttkmbb.com/api/v1/calculators/drywall · OpenAPI operationId `estimate_drywall_sheets` in https://tttkmbb.com/openapi.json
- Authentication: none. Rate limit: fair use, see https://tttkmbb.com/docs/rate-limits.md.

## MCP

- Server: `https://tttkmbb.com/mcp` (Streamable HTTP, JSON-RPC 2.0, no auth)
- Tool:  `run_calculator` with `{"calculator_id": "drywall", "inputs": {…}}`

## Example

- 15 ft × 12 ft × 8 ft room with ceiling, 4 × 8 sheets, 10 % waste: inputs `{"unit_system":"imperial","room_length":15,"room_width":12,"wall_height":8,"include_ceiling":true,"sheet_size":"4x8_ft","waste_percent":10}` → `{"area_ft2":612,"area_m2":56.86,"sheets_needed":22,"sheet_size_used":"4 × 8 ft","screws":612,"joint_compound_gallons":6.12,"joint_compound_liters":23.2,"compound_pails_4_5_gal":2}`
- 40 m² of wall, 1200 × 2400 mm boards, 10 % waste: inputs `{"unit_system":"metric","wall_area":40,"waste_percent":10}` → `{"area_m2":40,"area_ft2":430.56,"sheets_needed":16,"sheet_size_used":"1200 × 2400 mm","screws":431,"joint_compound_liters":16.3,"joint_compound_gallons":4.31,"compound_pails_4_5_gal":1}`

```
GET https://tttkmbb.com/api/v1/calculate/drywall?unit_system=imperial&room_length=15&room_width=12&wall_height=8&include_ceiling=true&sheet_size=4x8_ft&waste_percent=10
```

## Limitations

You need paint or wallpaper quantities for the finished wall (use paint or wallpaper), or metal-stud framing take-offs. Fastener spacing follows IRC R702.3.5 (screws at 16 in on walls and 12 in on ceilings with 16 in framing), which works out to roughly one screw per square foot. Compound coverage is USG's figure for taping and three-coat finishing of the joints. All values are computed from the formula above; no measurement or live data is involved.

## FAQ

**Should I subtract doors and windows?**

Usually not for standard openings: the cut-out pieces are rarely reusable, so most estimators ignore openings under about 2 m² and only deduct large ones via openings_area.

**Which sheet size should I choose?**

Use the longest sheets you can handle: 4 × 12 ft or 1200 × 3000 mm sheets reduce the number of joints to tape; 4 × 8 ft and 1200 × 2400 mm are the common DIY sizes.

**Is tape included?**

No. Joint tape is roughly 37 m per 100 m² (370 ft per 1,000 ft²) of board; corner bead is the sum of the outside-corner lengths.

## Related

- [Paint Calculator](https://tttkmbb.com/construction/paint.md) — Paint for the finished boards.
- [Wallpaper Calculator](https://tttkmbb.com/construction/wallpaper.md) — Paper for the finished boards.