Drywall Sheets, Paint Gallons, Siding Squares & Wallpaper Calculator

Calculate 4×8 and 4×12 drywall sheets, joint compound, paint gallons, siding squares, and wallpaper rolls.

4×8 Drywall Sheets & Paint Gallons Required
30 Sheets (4×8) • 5 Gal Paint
Total Surface: 865 sq ft (Walls: 565 + Ceiling: 300 sq ft) • 4×12 Option: 20 sheets
Joint Mud & Drywall Screws 43.3 gal mud • 960 screws
Paint Needed (2 Coats) 4.94 gal (Buy 5 gal)
Exterior Siding Squares 6.22 squares
Wallpaper Double Rolls 11 double rolls
Inputs
ft
Length of the room or structure in feet.
ft
Width of the room or structure in feet.
ft
Floor-to-ceiling wall height in feet.
sq ft
Standard door ≈ 21 sq ft; average window ≈ 15 sq ft.
Whether to include the ceiling surface in drywall and paint totals.
coats
2 coats recommended for full hide and durability.
sq ft/gal
Smooth drywall ≈ 350–400 sq ft/gal; textured/masonry ≈ 200–275 sq ft/gal.
Results & Graph
4×8 Drywall Sheets & Paint Gallons Required
30 Sheets (4×8) • 5 Gal Paint
Total Surface: 865 sq ft (Walls: 565 + Ceiling: 300 sq ft) • 4×12 Option: 20 sheets
Joint Mud & Drywall Screws
43.3 gal mud • 960 screws
Includes 10% cutting waste
Paint Needed (2 Coats)
4.94 gal (Buy 5 gal)
At 350 sq ft/gal coverage
Exterior Siding Squares
6.22 squares
1 square = 100 sq ft (+10% waste)
Wallpaper Double Rolls
11 double rolls
56 usable sq ft per double roll

Unfolded Room Elevation, Sheet Count & Multi-Coat Paint Suite

Net Wall Area, Ceiling Surface, and Door/Window Deductions
Graph 1 • Unfolded 4-Wall Perimeter & Ceiling Blueprint Shows wall elevations, door/window deductions, and ceiling area
Wall 1 (20'×9') Wall 2 (15'×9') Wall 3 (20'×9') Wall 4 (15'×9') Ceiling (20'×15') 300 sq ft Unfolded Perimeter = 70 ft × 9 ft − 65 sq ft Openings = 565 sq ft Net Wall Area
Graph 2 • Drywall Sheet Sizes, Siding Squares & Wallpaper Rolls Includes 10% cutting waste allowance
Standard 4×8 ft Drywall Panels (32 sq ft) 30 sheets Large 4×12 ft Drywall Panels (48 sq ft: Fewer Seams) 20 sheets Wallpaper Double Rolls (56 usable sq ft/roll) 11 rolls Exterior Siding Squares (100 sq ft/square) 6.21 squares
Graph 3 • Paint Gallons Needed Across 1 to 4 Coats Based on 865 sq ft surface area at 350 sq ft/gal
0 gal 5.3 gal 10.7 gal 1 Coat: 2.47 gal 2.5 1 Coat 2 Coats: 4.94 gal 4.9 2 Coats 3 Coats: 7.41 gal 7.4 3 Coats 4 Coats: 9.89 gal 9.9 4 Coats
Summary: Total surface area is 865 sq ft, requiring 30 4x8 drywall sheets and 5 gallons of paint.
Summary: A 20 ft × 15 ft room with 9 ft ceilings has 630 sq ft of gross wall area (565 sq ft net after deducting 65 sq ft for doors and windows) plus 300 sq ft of ceiling area, totaling 865 sq ft. Including 10% waste, hanging drywall requires 30 standard 4×8 sheets (or 20 4×12 sheets) and 43.3 gallons of joint compound. Painting 2 coats at 350 sq ft/gallon requires 4.94 gallons (5 one-gallon cans).

Formula & Mathematical Methodology: Net Surface Area, Drywall Sheet Count & Multi-Coat Paint Volume

Atotal = 2(L + W)H − Aopenings + Aceiling,   Sheets4×8 = [Atotal × 1.1032],   Paint (gal) = [Atotal × Coats350]
A_total = 2(L + W)H − A_openings + A_ceiling; Sheets_4x8 = ⌈(A_total × 1.10) / 32⌉; Gal_paint = ⌈(A_total × Coats) / 350⌉
  • Atotal: Net wall area plus optional ceiling area in square feet
  • 32 / 48: Square feet per 4×8 sheet (32 sq ft) or 4×12 sheet (48 sq ft)

Rounding: Material package counts (sheets, gallon cans, rolls) round up to whole units; exact areas round to 1–2 decimal places.

Worked Example: 20' × 15' Room with 9' Ceilings (Including Ceiling, 65 sq ft Openings, 2 Coats)

Estimate drywall and paint for a 20 × 15 ft living room with 9 ft walls and 65 sq ft of doors/windows.

  1. Gross wall area = 2 × (20 + 15) × 9 = 630 sq ft; net wall area = 630 − 65 = 565 sq ft.
  2. Add ceiling (20 × 15 = 300 sq ft) → Total surface = 865 sq ft.
  3. Drywall 4×8 sheets (+10% waste) = ⌈(865 × 1.10) ÷ 32⌉ = 30 sheets; Paint (2 coats) = ⌈(865 × 2) ÷ 350⌉ = 5 gallons.
Result: Requires 30 sheets of 4×8 drywall (or 20 sheets of 4×12) and 5 gallons of paint.

Frequently Asked Questions

When should I choose 4×12 drywall sheets instead of 4×8 sheets?

In rooms with dimensions divisible by 12 ft (and when you have a helper or drywall lift), hanging 4×12 sheets horizontally eliminates up to 33% of butt joints, cutting taping and sanding time significantly.

How much joint compound (mud) and tape do I need per 100 sq ft of drywall?

Plan on roughly 0.05 gallons of ready-mixed joint compound (about 1 five-gallon bucket per 1,000 sq ft) and 37 linear feet of paper joint tape per 100 sq ft of gypsum board.

Construction & Home • Interior & Exterior Finishes Guide

How to Use the Drywall Sheets, Paint Gallons, Siding Squares & Wallpaper Calculator: Practical Guide & Visual Analysis

Plan interior and exterior wall finishes from room length, width, ceiling height, and window/door openings. Instantly compute 4×8 or 4×12 Sheetrock panel counts, joint mud and screws, multi-coat paint gallons, exterior siding squares (100 sq ft), and wallpaper rolls. Whether you are researching drywall calculator, sheetrock calculator, paint calculator, how many gallons of paint, vinyl siding calculator, this interactive tool helps you estimate 4×8 and 4×12 drywall sheets, joint compound mud, drywall screws, interior/exterior paint gallons by coat count, vinyl/lap siding squares, and wallpaper double rolls from room dimensions.

Interpreting the 3 Custom Visual Graphs & Key Outputs

As you adjust Room / Building Length (Feet), Room / Building Width (Feet), Wall / Ceiling Height (Feet), Doors & Windows Deduction Area, the calculator immediately computes 4×8 ft (32 sq ft) and 4×12 ft (48 sq ft) Drywall Sheet Counts (+10% Waste), Ready-Mix Joint Compound (Gallons) & Drywall Screws, Paint Gallons Required for Selected Coats, Exterior Siding Squares (100 sq ft) & Wallpaper Double Rolls and updates all three domain-specific SVG charts in real time. Instead of relying on a single static figure, you can inspect the primary domain diagram, component breakdown, and multi-point trajectory curve to see how changing your inputs shifts the final result. Use the Compare (up to 3 scenarios) button to evaluate side-by-side variations before making a decision.

Real-World Benchmark & Planning Tips (Global Construction & ASTM C840 Gypsum Board Standard)

In our benchmark scenario (20' × 15' Room with 9' Ceilings (Including Ceiling, 65 sq ft Openings, 2 Coats)), Requires 30 sheets of 4×8 drywall (or 20 sheets of 4×12) and 5 gallons of paint. Keep in mind that includes a 10% cutting and fitting waste factor for drywall panels and exterior siding. For related calculations in Construction & Home, explore Board Foot, Lumber Weight, Wall Stud Framing & Board-and-Batten Calculator, Roofing, Stair Stringer, Tile, Mulch/Gravel & HVAC BTU Calculator, Concrete & Square Footage Calculator.