Wall Square Footage Calculator

Figure out the square footage of any wall for painting, wallpaper, or siding. Enter length, height, and openings to get net area and material cost.

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Wall Dimensions

Wall Length

Wall Height

Number of Walls

Openings (Doors & Windows)

Total Door Area

Total Window Area

Waste Factor

Cost Details

Cost per Square Foot

$ /ft²

Additional Cost

Wall Square Footage Summary

Total Area: —

Area per Wall—

Gross Wall Area—

Total Openings Area—

Net Wall Area—

Area with Waste—

Estimated Material Cost—

Estimated Total Cost—

Component	Value	Unit

Enter details and calculate to see breakdown.

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Faiq Ur Rahman is a web designer, digital product developer, and Founder of Techraxy, a growing platform of online calculators and utility tools. He specializes in building structured, user-friendly tools focused on finance, health, conversions, productivity, and everyday problem-solving. He is passionate about developing practical digital solutions that make complex tasks simpler for users worldwide.

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Introduction

Nobody paints a wall as if it were a blank rectangle. A 16 ft × 8.5 ft bedroom wall sounds like 136 square feet until you subtract a 20-square-foot window and a 21-square-foot door. That’s 95 square feet of actual surface. Multiply by three walls in the room and the difference between gross and net is 123 square feet. A gallon of paint covers about 350 square feet. That’s most of a gallon of paint you didn’t need.

The calculator does that subtraction and lets you price the result. It also adds a waste allowance, which is the third lever most people forget. A gallon isn’t enough if you’re cutting in around trim or rolling out a second coat on a textured wall. Ten percent waste covers a surprising amount of real-world loss.

This page works for any material sold by square footage: paint, wallpaper, beadboard, tile backsplash, exterior siding, or drywall. Change the cost-per-square-foot field to match the material and the output is a material budget.

How to Use the Wall Square Footage Calculator

Set the currency from the dropdown if your supplier doesn’t quote in US dollars.
Enter the length of a single wall and pick the unit, feet, inches, yards, meters, centimeters, or millimeters.
Enter the wall height and pick its unit.
Enter how many walls have the same dimensions. A room with four identical walls uses 4.
Enter the total door area. Standard interior doors run about 21 square feet each. Pick square feet, square meters, or square inches.
Enter the total window area. A 3 ft × 5 ft window is 15 square feet.
Set the waste factor. Ten percent is a reasonable default for painting or paneling.
Enter the cost per square foot for your material.
Add any flat additional cost: primer, tape, drop cloths, disposal.
Hit Calculate. The Summary tab shows net area and total cost. The Detailed Breakdown tab lists gross area, per-wall area, and every conversion.

How the Wall Square Footage Formula Works

Everything converts to feet before the area math runs.

Formula: Area per Wall (ft²) = Length (ft) × Height (ft)

Formula: Gross Wall Area (ft²) = Area per Wall × Number of Walls

Formula: Net Wall Area (ft²) = Gross Area − Door Area − Window Area

Formula: Area with Waste (ft²) = Net Wall Area × (1 + Waste % ÷ 100)

Formula: Material Cost = Area with Waste × Cost per ft²

Formula: Total Cost = Material Cost + Additional Cost

The gross area comes from a simple length × height product. Multiply by the wall count and you have the surface area before openings. Door area and window area subtract next. Those two fields accept square feet, square meters, or square inches. A 3 ft × 5 ft window entered as 15 ft² is identical to the same window entered as 1.39 m² or 2,160 in².

Waste applies to the net area, not the gross. That’s deliberate. You don’t waste material on a window you never covered. The waste multiplier is the last step before the cost calculation, so the cost line already reflects the overage.

The cost per square foot is entered manually. The tool doesn’t know whether you’re pricing Benjamin Moore Regal or a box of vinyl plank. Enter your own number and the material cost scales accordingly.

Worked Example

You’re painting a home office. Three walls, each 15 ft long and 8.5 ft tall. One entry door at 21 ft². Two windows, each 12 ft², for 24 ft² total. Waste factor 10%. Paint runs $0.32 per square foot for two coats, and you’re adding $45 for primer and supplies.

Step 1: Area per wall.
15 × 8.5 = 127.5 ft².

Step 2: Gross wall area.
127.5 × 3 = 382.5 ft².

Step 3: Total openings.
21 + 24 = 45 ft².

Step 4: Net wall area.
382.5 − 45 = 337.5 ft².
In square meters: 337.5 × 0.092903 = 31.35 m².

Step 5: Apply 10% waste.
337.5 × 1.10 = 371.25 ft².

Step 6: Material cost.
371.25 × $0.32 = $118.80.

Step 7: Total cost.
$118.80 + $45.00 = $163.80.

The Summary tab reads: 127.5 ft² per wall, 382.5 ft² gross, 45 ft² openings, 337.5 ft² net (31.35 m²), 371.25 ft² with waste, $118.80 material cost, $163.80 total. The breakdown tab lists every conversion.

Bump the waste factor to 15% and the material cost climbs to $124.20. The difference is one more quart of paint.

Frequently Asked Questions

How do I measure the square footage of a wall?

Multiply the wall length by its height in feet. A 12 ft × 8 ft wall is 96 square feet. If there are multiple walls with the same dimensions, multiply that figure by the count. Subtract any doors and windows. Add 10% for waste if you’re ordering paint or wallpaper.

Do I need to subtract windows and doors?

For paint, wallpaper, and paneling, yes. For drywall, exterior sheathing, or insulation, no — those materials go behind the openings. The calculator gives you both numbers, so pick whichever matches the material you’re buying.

How much does a gallon of paint cover?

About 350 to 400 square feet for one coat on a smooth, previously painted wall. Two coats drops that to 175 to 200 square feet per gallon. Textured walls, porous new drywall, and dark-to-light color changes all reduce coverage. The paint can label is the authority for a specific product.

How much does it cost to paint a room?

Material alone runs $0.25 to $0.60 per square foot for two coats of mid-grade interior paint. A 12 ft × 12 ft room with 8 ft ceilings has about 384 square feet of gross wall, minus openings, plus waste. That’s roughly $90 to $220 in paint. Professional labor adds $1.50 to $3.50 per square foot of wall area.

What’s the difference between wall area and floor area?

Floor area is the footprint of the room (length × width). Wall area is the vertical surface (length × height). A 12 ft × 12 ft room has 144 square feet of floor but 384 square feet of gross wall area at 8 ft ceilings. The two figures serve different purposes and both matter for a remodel budget.

Do I need to include the ceiling in the wall area?

No. Ceilings are a separate calculation. Add ceiling area if you’re painting the ceiling too. A flat ceiling is length × width of the room. Sloped or vaulted ceilings need their own triangle or trapezoid math. The wall calculator doesn’t model ceilings.

How much waste factor should I use?

Ten percent for standard interior paint on smooth walls. Fifteen percent for textured walls or heavy trim. Twenty percent for wallpaper with pattern matching. Ten to fifteen percent for paneling or siding. Extra material costs a little; running short costs a trip to the store and possibly a dye-lot mismatch on the new batch.

What if the walls have different heights?

Run each height separately. Enter the length and height for the shorter walls, get the area, then do the same for the taller walls and add the totals. The calculator handles one height per run. For rooms with multiple heights, two quick passes cover it.

Can I use this calculator for exterior walls?

Yes. Exterior wall area for paint, siding, or stain uses the same formula. Measure the perimeter of the house, multiply by the wall height, subtract doors and windows. Gable ends and angled wall sections need separate triangle math. The calculator works for rectangular exterior walls directly.

How do I convert square feet to square meters for a wall?

Multiply square feet by 0.092903. A 337.5 ft² wall becomes 31.35 m². Going the other way, multiply square meters by 10.7639. The calculator shows both units on the summary line, so you don’t need to convert by hand.

What’s the difference between a wall’s gross area and paintable area?

Gross area includes openings. Paintable area excludes them. Paint manufacturers sometimes call it “spreadable area” or “usable area.” Same concept. Subtract the openings to get the number you actually paint. Trim, doors, and windows get their own paint, often in a different sheen.

Is this wall square footage calculator free?

Yes. No sign-up, no email, no limit on how many walls you calculate. Everything runs in your browser. Use the Copy button to save the numbers for a paint quote, or Share to send them to whoever’s holding the roller.

Disclaimer

This calculator provides planning estimates for wall area and material cost based on the dimensions you enter. It assumes rectangular walls with no sloped or angled sections. Actual material requirements vary with surface texture, product coverage rates, application method, and manufacturer packaging. Verify coverage rates against the product label before ordering. Cost figures are user-entered estimates only and do not include taxes, labor, or equipment unless you enter them separately. For large or complex remodels, confirm scope with a licensed contractor.