How to Calculate Square Footage

Square footage is the area of a space measured in square feet (ft$^2$). It tells you how much flat surface a room, yard, wall, or floor covers. Whether you are buying flooring, ordering paint, pricing sod, or listing a home, you need to know the square footage.

The core idea is simple: measure the length and width of a space in feet, then multiply. Most of this page is about handling the situations that make real rooms trickier than textbook rectangles — L-shapes, alcoves, mixed units, and material waste.

Square Footage of a Rectangular Room

For any rectangular space, square footage is length times width, with both measurements in feet:

$A = L \times W$

A room that is 14 ft long and 11 ft wide has an area of:

$A = 14 \times 11 = 154 \text{ ft}^2$

Important: Both measurements must be in feet before you multiply. If one dimension is in inches, yards, or meters, convert it to feet first (see the conversion section below).

Square Footage of an L-Shaped Room

Most real rooms are not perfect rectangles. An L-shaped room is the most common irregular layout. The strategy is to split the L into two rectangles, calculate each area, and add them together.

How to split this room:

1. Draw a vertical line where the room steps inward (the dashed blue line)
2. Rectangle A is the full left section: 10 ft wide and 14 ft tall
3. Rectangle B is the lower-right section: 8 ft wide and 8 ft tall

$A_A = 10 \times 14 = 140 \text{ ft}^2$

$A_B = 8 \times 8 = 64 \text{ ft}^2$

$A_{\text{total}} = 140 + 64 = 204 \text{ ft}^2$

There is more than one way to split an L-shape. You could also draw a horizontal line at the step, creating a top rectangle (10 ft by 6 ft = 60 ft$^2$) and a bottom rectangle (18 ft by 8 ft = 144 ft$^2$). Either way, the total is still 204 ft$^2$ — the method does not change the answer. That is a good self-check.

Square Footage with Alcoves and Closets

If a room has a walk-in closet, bay window alcove, or built-in nook, measure each section separately and add them to the main room area.

For example, a bedroom that is 12 ft by 10 ft with a 3 ft by 5 ft closet alcove:

$A_{\text{room}} = 12 \times 10 = 120 \text{ ft}^2$

$A_{\text{closet}} = 3 \times 5 = 15 \text{ ft}^2$

$A_{\text{total}} = 120 + 15 = 135 \text{ ft}^2$

If the alcove is already included in the room dimensions you measured, do not add it again. Sketch your room on paper and label where each measurement starts and ends to avoid double-counting.

Converting Units to Feet First

Before multiplying, every measurement must be in feet. Here are the most common conversions:

Example: A room is 150 inches long and 10 ft wide. Convert inches to feet first:

$150 \div 12 = 12.5 \text{ ft}$

Then calculate: $12.5 \times 10 = 125 \text{ ft}^2$.

Unit Conversions FROM Square Feet

Once you have the square footage, you may need to convert to other area units for purchasing or planning:

Why divide by 9 for square yards? One yard equals 3 feet, so one square yard equals $3 \times 3 = 9$ square feet. The conversion factor is squared because area is two-dimensional.

Worked Examples

Example 1: Simple rectangular room

A bedroom measures 14 ft by 11 ft. Find the square footage.

$A = 14 \times 11 = 154 \text{ ft}^2$

Answer: The bedroom is 154 square feet.

Example 2: Room measured in feet and inches

A dining room measures 12 ft 6 in by 10 ft 3 in. Find the square footage.

Step 1 — Convert inches to feet:

$12 \text{ ft } 6 \text{ in} = 12 + \frac{6}{12} = 12.5 \text{ ft}$

$10 \text{ ft } 3 \text{ in} = 10 + \frac{3}{12} = 10.25 \text{ ft}$

Step 2 — Multiply:

$A = 12.5 \times 10.25 = 128.125 \text{ ft}^2$

Answer: The dining room is approximately 128.13 square feet. For material ordering, round up to 129 ft$^2$.

Example 3: L-shaped living room

A living room has an L-shape. The main section is 20 ft by 15 ft, and a smaller section extends 8 ft by 6 ft off the side. Find the total square footage.

Step 1 — Find each rectangle’s area:

$A_1 = 20 \times 15 = 300 \text{ ft}^2$

$A_2 = 8 \times 6 = 48 \text{ ft}^2$

Step 2 — Add them together:

$A_{\text{total}} = 300 + 48 = 348 \text{ ft}^2$

Answer: The L-shaped living room is 348 square feet.

Example 4: Calculating paint needed

A rectangular room is 16 ft long, 12 ft wide, and 9 ft tall. You need to paint all four walls (ignore windows and doors for a rough estimate). One gallon of paint covers approximately 350 ft$^2$. How many gallons do you need?

Step 1 — Find the wall areas. There are two pairs of walls:

$A_{\text{long walls}} = 2 \times (16 \times 9) = 2 \times 144 = 288 \text{ ft}^2$

$A_{\text{short walls}} = 2 \times (12 \times 9) = 2 \times 108 = 216 \text{ ft}^2$

Step 2 — Total wall area:

$A_{\text{walls}} = 288 + 216 = 504 \text{ ft}^2$

Step 3 — Divide by coverage per gallon:

$\frac{504}{350} \approx 1.44 \text{ gallons}$

Answer: You need 2 gallons of paint (round up, since you cannot buy 0.44 of a gallon). If you plan two coats, double the area to 1,008 ft$^2$ and buy 3 gallons.

Example 5: Flooring with waste factor

A kitchen is 13 ft by 10 ft. You are installing tile flooring. The contractor recommends adding 10% for cuts and waste. How many square feet of tile should you order?

Step 1 — Base area:

$A = 13 \times 10 = 130 \text{ ft}^2$

Step 2 — Add 10% waste:

$130 \times 0.10 = 13 \text{ ft}^2$

$130 + 13 = 143 \text{ ft}^2$

Answer: Order 143 square feet of tile. For complex patterns (diagonal, herringbone), increase the waste factor to 15%, giving $130 \times 1.15 = 149.5 \approx 150 \text{ ft}^2$.

Common Square Footage Reference

This table gives typical room sizes to help you estimate before measuring:

Real-World Application: Estimating Materials for a Home Renovation

You are renovating a basement that has two areas: a main room (22 ft by 16 ft) and an attached laundry area (8 ft by 10 ft). You need to order vinyl plank flooring and baseboards.

Step 1 — Calculate total floor area:

$A_{\text{main}} = 22 \times 16 = 352 \text{ ft}^2$

$A_{\text{laundry}} = 8 \times 10 = 80 \text{ ft}^2$

$A_{\text{total}} = 352 + 80 = 432 \text{ ft}^2$

Step 2 — Add 10% waste for flooring:

$432 \times 1.10 = 475.2 \text{ ft}^2$

Round up: order 476 square feet of flooring.

Step 3 — Calculate baseboard length. Baseboards go along the perimeter of the walls, minus doorways. Main room perimeter: $2(22 + 16) = 76$ ft. Laundry perimeter: $2(8 + 10) = 36$ ft. Subtract the shared wall opening (assume a 4 ft doorway) and the exterior door (3 ft):

$76 + 36 - 4 - 4 - 3 = 101 \text{ ft of baseboard}$

We subtract the shared opening twice (once from each room’s perimeter) since you do not install baseboard across a doorway.

Step 4 — Convert flooring to square yards (if purchasing carpet instead):

$\frac{432}{9} = 48 \text{ sq yd}$

Answer: You need approximately 476 ft$^2$ of flooring (with waste) and 101 linear feet of baseboard trim.

Practice Problems

Test your understanding with these problems. Click to reveal each answer.

Key Takeaways

• Square footage = length (in feet) times width (in feet) — always convert to feet before multiplying
• For L-shaped rooms, split into rectangles, calculate each area, and add them together
• For alcoves and closets, measure each section separately and add to the main area
• Convert inches to feet by dividing by 12; convert square feet to square yards by dividing by 9
• When ordering flooring, add 10% for waste (15% for complex patterns like diagonal or herringbone)
• When calculating paint, find the total wall area (not floor area) and divide by the coverage per gallon (typically 350 ft$^2$)
• Always round up when buying materials — you cannot purchase a fractional gallon or partial tile box

Return to Geometry for more topics in this section.