Square Footage Calculator

What This Calculator Does

This square footage calculator finds the floor area of any room — rectangular, triangular, circular, or L-shaped. Enter the dimensions and it instantly shows the area in square feet, square meters, and square yards. Use the multi-room feature to add every room on a floor and get a combined total for the entire space.

The calculator also shows how much material to order for flooring or other projects that require waste allowances. A 10% overage is standard for straight-lay installation; 15% is recommended for diagonal or herringbone patterns where more cuts are required at the edges. These estimates appear automatically once you enter your room dimensions.

All inputs are in feet by default. If your measurements are in inches, divide each dimension by 12 before entering. If your measurements are in meters, you can enter them as-is — just remember the results will then be in square meters, not square feet, because the conversion assumes feet as the input unit.

How to Measure a Room: Step-by-Step

Measuring a room accurately before you start any project prevents wasted material and costly trips back to the hardware store. Here is the process for standard rectangular rooms:

1. Clear the perimeter. Move furniture away from walls so you can measure along the baseboard level, not around objects. Measuring at baseboard height gives the true floor-level dimensions rather than a slightly narrower reading from the middle of the room.
2. Measure length first. Stretch your tape from wall to wall along the longest dimension. Write it down immediately — do not trust memory when you have multiple rooms. Measure twice if you are buying expensive materials.
3. Measure width. Measure the perpendicular dimension from the same corner. For rectangular rooms, width is the shorter wall.
4. Note alcoves, closets, and bay windows. Decide whether to include them. For flooring, you typically include everything the floor covers, including inside closets and under door frames. For paint, you might exclude inside closets or treat them separately if they are a different color.
5. Record in decimal feet, not feet and inches. Calculators work in decimal form — 10 feet 6 inches should be entered as 10.5 feet. To convert inches to a decimal fraction, divide inches by 12: 10 ft 9 in = 10 + (9÷12) = 10.75 ft.

For flooring specifically, measure at the widest and longest points of each room, even if they are slightly wider due to a recessed area — flooring installers cut to fit, so buying to the widest dimension is correct. If there is a hallway connecting rooms, measure and add it as a separate rectangular section.

Square Footage Formulas for Every Room Shape

Not all rooms are simple rectangles. Here are the exact formulas used by this calculator for each supported shape, along with worked examples.

Rectangle (including squares)

Example: A living room is 18 feet long and 14 feet wide.

Area = 18 × 14 = 252 sq ft

This is the most common room shape. Bedrooms, kitchens, and hallways are nearly always rectangular. Even rooms that are not perfectly square are close enough to use the rectangle formula — small irregularities at corners rarely affect material calculations meaningfully.

Triangle

Example: An attic room has a triangular floor plan with a base of 20 feet and a perpendicular height of 12 feet.

Area = (20 × 12) ÷ 2 = 120 sq ft

The height in the triangle formula must be the perpendicular height — the measurement from the base to the opposite vertex at a 90° angle. If you only have the three side lengths, you can use Heron's formula, but for most architectural spaces the perpendicular height is measurable directly.

Circle

Example: A round sunroom has a diameter of 16 feet.

Radius = 16 ÷ 2 = 8 ft → Area = π × 8² = π × 64 ≈ 201.06 sq ft

Circular rooms are uncommon but appear in towers, rotundas, and round garden rooms. The diameter is the easiest measurement to take — stretch a tape across the widest point through the center. You can also measure the circumference with a flexible tape and divide by π to get the diameter.

L-Shape (two rectangles)

Example: An open-plan kitchen and dining area forms an L-shape. The kitchen portion is 14 ft × 10 ft and the dining alcove is 6 ft × 8 ft.

Main = 14 × 10 = 140 sq ft · Extension = 6 × 8 = 48 sq ft · Total = 188 sq ft

When dividing an L-shaped room into two rectangles, there is no single "correct" way to split it — any division into two non-overlapping rectangles that together fill the room is valid. Choose the split that makes measurement easiest. You can verify your division by measuring the full outer rectangle and subtracting the missing corner.

Calculating Square Footage for Flooring

Flooring is one of the most common reasons people calculate square footage. Getting the number right before you shop prevents both costly overpurchase and the frustrating situation of running out of material mid-installation. Here is a complete walkthrough.

Step 1 — Measure every area the floor covers

Include closets, alcoves, under open doorways, and any thresholds. Flooring runs wall-to-wall under the baseboard, so measure the full room dimensions rather than just the open walking area.

Step 2 — Add rooms together for a whole-floor total

If you are laying the same flooring throughout a hallway and three bedrooms, add all four rooms together before calculating your purchase quantity. Buying as a single order is often cheaper per unit and ensures all planks come from the same production run, which matters for hardwood where color and grain can vary between batches.

Step 3 — Apply the waste factor

Flooring is almost never installed perfectly without any cuts. Waste comes from:

• Cut pieces at the end of rows that are too short to use
• Pieces discarded due to defects or damage during installation
• Pattern matching for wood or tile with directional patterns
• Future repairs — keeping extra material ensures patches match

Standard waste allowances by installation type:

Step 4 — Convert to boxes

Most flooring is sold in boxes labeled with how many square feet each box covers. Divide your total needed (after waste factor) by the box coverage and round up to the nearest whole box. Never round down — running out of material mid-project means waiting on backorders that may arrive from a different production batch.

Example: You have three rooms totaling 480 sq ft. Adding 10% waste = 528 sq ft needed. Each box covers 22.4 sq ft. 528 ÷ 22.4 = 23.57 → order 24 boxes.

Calculating Paint Quantity from Square Footage

Square footage is also the basis for estimating how much paint to buy. The process differs from flooring because you are covering walls and ceilings, not floor area — and you need to account for doors and windows that you will not paint.

Wall area calculation

To find the total wall area of a room, calculate the perimeter of the room (sum of all four wall lengths) and multiply by the ceiling height.

Example: A 14 × 12 ft room with 9-foot ceilings.

Perimeter = 2 × (14 + 12) = 52 ft · Wall area = 52 × 9 = 468 sq ft

Subtracting doors and windows

A standard interior door is approximately 20 sq ft (2.5 ft × 8 ft). A standard window is roughly 15 sq ft (3 ft × 5 ft). Subtract these from your wall area for a more accurate estimate, though many painters skip this step and simply count it as extra for a second coat.

Paint coverage and coats

Most interior wall paints cover 350–400 square feet per gallon on smooth walls in a single coat. Textured walls, porous surfaces, and very dark colors require more paint. For new drywall, always plan for two coats — primer plus paint. For repainting a similar color, one coat often suffices.

For the 14 × 12 room example: 468 sq ft ÷ 375 sq ft/gallon ≈ 1.25 gallons per coat. Buy 2 gallons to have enough for two coats with a little left over for touch-ups.

Other Common Uses for Square Footage

Square footage calculations come up across many home and property contexts beyond flooring and paint:

• Real estate valuation.Price per square foot is the standard comparison metric for home sales. In a given neighborhood, if comparable homes sell for $250/sq ft and a home is 2,000 sq ft, the indicated value is $500,000. Understanding a home's total square footage — and whether listed square footage includes or excludes basement, garage, or unfinished space — is essential for any purchase comparison.
• HVAC sizing. Air conditioners and heat pumps are rated in BTUs per hour and sized based on square footage. A rule of thumb is 20 BTUs per square foot for cooling. A 1,500 sq ft home needs approximately 30,000 BTUs — equivalent to a 2.5-ton air conditioner. Climate zone, ceiling height, and insulation quality all modify this calculation, but square footage is the starting point.
• Landscaping and sod.Grass seed, sod, mulch, and fertilizer are all sold by the square foot or square yard of coverage. Measuring your lawn's total area (often irregular shapes that can be broken into rectangles and triangles) tells you exactly how much product to buy.
• Tile work. Kitchen backsplashes, bathroom tile, and outdoor pavers all require square footage measurements. The same waste factor rules apply: 10% for straight layouts, 15% for diagonal, with larger tiles requiring slightly less waste than small mosaic tiles.
• Rental pricing. Commercial leases are priced per square foot per year — a 1,200 sq ft office at $30/sq ft/year costs $36,000 annually, or $3,000 per month. Knowing the exact square footage you are renting is essential for comparing lease rates across different spaces.

Common Mistakes When Measuring Square Footage

These are the errors that consistently cause people to buy too much or too little material:

• Forgetting to convert inches to decimal feet. A room that is 11 feet 9 inches is 11.75 feet, not 11.9. Always divide the inch portion by 12.
• Not measuring closets. Closets need flooring too. A typical walk-in closet adds 30–50 sq ft — significant enough to matter when buying planks or tiles.
• Measuring at counter height instead of floor level. In rooms where cabinets or furniture hug the walls, measure at baseboard level, not at the top of the furniture, to get true floor dimensions.
• Confusing perimeter with area. The perimeter of a 10 × 12 room is 44 feet (the distance around the edge). The area is 120 square feet. These are completely different measurements used for completely different purposes — perimeter for trim and molding, area for flooring and paint.
• Skipping the waste factor. This is the most expensive mistake. Buying exactly the square footage of a room always leaves you short because of cut waste. The 10% waste allowance is not optional — it is a reality of installation.
• Treating staircase landings as rectangles when they are not. Measure each stair and landing individually. A standard stair is 36 inches wide and 10–11 inches deep; multiply by the number of steps and add the landings separately.

Frequently Asked Questions