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Wall Square Footage Calculator

Ready to calculate
Openings Subtracted.
Paint + Drywall + Wallpaper.
2-Coat Paint Math.
100% Free.
Privacy Secure.

How it Works

01Wall Size

Enter wall length and height in feet. L × H = gross area.

02Doors & Windows

Count openings. Default 3×7 doors, 3×4 windows — or customize.

03Net Paintable

Gross minus openings = paintable net area.

04Materials

Paint (2 coats), drywall sheets, and wallpaper rolls — all at once.

What is a Wall Square Footage Calculator?

A wall square footage calculator — also called a wall area calculator, paintable area calculator, or drywall sheet calculator — takes wall length and height, subtracts door and window openings, and gives you the net paintable area plus exact paint gallons, drywall sheets, and wallpaper rolls to buy. Paint stores and hardware associates love selling you 20% extra "just in case" material — this tool shows the honest number based on industry-standard coverage rates.

Uses professional painter coverage standards: 350 ft² per gallon for two-coat paint (published by Sherwin-Williams and Benjamin Moore for latex interior on primed drywall), 32 ft² per 4×8 sheet of drywall, and 56 ft² per US double roll of wallpaper. Default opening sizes are 3×7 ft for doors (standard residential pre-hung interior) and 3×4 ft for windows (standard double-hung); all four dimensions are customizable for larger sliding doors, picture windows, or custom openings.

The calculation is critical because openings routinely remove 25-40% of a wall's paintable area. A 12 ft × 8 ft bedroom wall with 1 door (21 ft²) and 1 window (12 ft²) loses 33 ft² of its 96 ft² gross — over a third. Forget to subtract and you'll overbuy paint by 50% and wallpaper by 100% (wallpaper rolls don't return well).

The tool distinguishes between gross area (used for drywall counts, because openings are framed with full sheets before cutting) and net paintable area (used for paint and wallpaper). Drywall scrap from cutouts is typically saved for small patches, not credited to the sheet count.

Great for DIY homeowners planning room refreshes and nursery repaints; painters writing quotes and ordering enough for the whole job in one trip; drywall installers sheet-counting for new construction, patches, and additions; wallpaper installers matching rolls and avoiding dye-lot mismatches on re-orders; and landlords pricing unit turnover repaints.

How It Works

Gross area = wall length × wall height (ft²).
Deductions = doors × (door_width × door_height) + windows × (window_width × window_height).
Net paintable = gross − deductions. Paint and wallpaper use this number.
Paint = ceil(net / 350) for 2 coats. Primer not included (add 1 gallon per 400 ft² if needed).
Drywall sheets = ceil(gross / 32). Uses gross because openings are framed before sheet is cut (only small scraps are saved).

Wall SqFt Formula

Gross_ft² = Length × Height
Deductions = N_doors × (W_door × H_door) + N_windows × (W_win × H_win)
Net_paintable = Gross − Deductions
Paint_gallons = ceil(Net_paintable / 350)   // 2 coats, 350 ft²/gal
Drywall_sheets = ceil(Gross / 32)          // 4 × 8 ft sheet
Wallpaper_rolls = ceil(Net_paintable / 56) // US double roll
Defaults: door 3 × 7 = 21 ft², window 3 × 4 = 12 ft²
Real-World Example

Worked Example

A 12 ft × 8 ft bedroom wall with 1 door (3×7) and 1 window (3×4):

  • Gross = 12 × 8 = 96 ft²
  • Deductions = 1×21 + 1×12 = 33 ft²
  • Net paintable = 96 − 33 = 63 ft²
  • Paint = ceil(63 / 350) = 1 gallon (2 coats)
  • Drywall = ceil(96 / 32) = 3 sheets
  • Wallpaper = ceil(63 / 56) = 2 double rolls

Who Uses This Calculator?

1
DIY homeowners planning paint projects and room refreshes
2
Painters writing quotes and ordering enough for the whole job in one trip
3
Drywall installers sheet-counting for new walls, patches, and additions
4
Wallpaper installers matching rolls and avoiding dye-lot issues on re-orders
5
Landlords and property managers scoping apartment turnover repaints

Technical Reference

Paint coverage — Sherwin-Williams: 250-400 ft²/gal first coat, 400-500 ft²/gal second coat. Average 350 ft²/gal for 2-coat systems on drywall. Deep tones and raw drywall need primer + 2 coats (3 total).

Gypsum Board (ASTM C1396) — standard 4×8 ft sheet = 32 ft². 4×10 and 4×12 also common (40 and 48 ft²). This tool uses the 4×8 default.

Wallpaper roll standards — US 'single roll' sold as 'double roll' (56 ft² / ~5.2 m² per roll). Euro rolls are 27-30 ft² singles. European wallpaper often requires more rolls than US rolls for the same area.

Key Takeaways

The easiest wall-material mistake is forgetting to subtract doors and windows — a typical 12×8 ft bedroom wall has 30%+ of its area lost to openings. Paint covers 350 ft²/gallon on two coats (not 400 — that's one coat, insufficient on light or raw drywall). Always buy 1 extra quart per 400 ft² for touch-ups, because dye lots change batch-to-batch and you can't re-match later. Drywall uses gross area because openings get framed before cutting; save cutoff scraps in a pile for small patches — they add up. Wallpaper needs US double rolls (56 ft²), not European single rolls (27-30 ft²) — double-check the box. Deep tones and rich colors often need primer + 2 coats (3 coats total), cutting effective coverage from 350 ft²/gal to about 200 ft²/gal. Always ask the paint store which finish system matches your color choice before you commit to gallon counts.

Frequently Asked Questions

How do I calculate square footage of a wall?
Multiply wall length by wall height (both in feet). A 12×8 ft wall = 96 sq ft gross. Subtract the area of any doors and windows to get the paintable net area.
How much paint do I need for a 12×12 room?
At 8 ft ceilings with 1 door and 1 window, four walls total ~350 ft² net. With 2 coats, you need about 2 gallons of paint plus 1 gallon of primer for raw drywall.
How many square feet does a gallon of paint cover?
350-400 ft² per gallon for 2-coat coverage on drywall. 250-300 ft²/gal on raw drywall (soaks up more). Dark or rich colors may need 3 coats = 250 ft²/gal effective coverage.
Do I subtract doors and windows from paintable area?
Yes — always subtract openings from paint and wallpaper calculations. A typical 3×7 door takes up 21 ft², a 3×4 window 12 ft². Large sliding doors or picture windows can remove 30%+ of a wall.
How many sheets of drywall for a 12×8 wall?
3 sheets of 4×8 drywall (96 sq ft ÷ 32 sq ft/sheet = 3). Drywall uses gross area because openings are framed before cutting, so you still need full sheets.
How many rolls of wallpaper do I need?
US double rolls cover ~56 ft² each. A 63 ft² bedroom wall needs 2 double rolls. European rolls are smaller (27-30 ft² per roll) — check the box before buying.
Should I buy extra paint?
Yes — always buy 1 extra quart per 400 ft² for touch-ups, second-year refreshes, and matching the same dye lot. Returning unopened paint is allowed at most stores, but dye lots change batch-to-batch.
Does paint coverage depend on the color?
Yes, strongly. White and light pastels cover in 1-2 coats. Deep reds, navy blues, and blacks often need tinted primer plus 2-3 finish coats (effective coverage drops to 200 ft²/gal from 350). Sheen matters too — flat absorbs more, gloss goes further.
How do I calculate paint for an accent wall?
Same formula, just one wall. Length × height, minus any openings, divided by 350 for 2 coats. A 12×8 accent wall with no openings = 96 ft² / 350 = 1 gallon (rounded up).
Is drywall sold in different sizes?
Yes. Standard 4×8 (32 ft²) is easiest to handle. 4×10 (40 ft²) is common for 10 ft ceilings. 4×12 (48 ft²) reduces seams but requires 2 people to carry. Contractors often prefer larger for fewer seams.

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The ToolsACE Team

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Disclaimer

Educational reference. Paint coverage varies by color, porosity, and primer. Always add 10-15% for cuts and waste when ordering.