# Square Footage Calculator

> Calculate area in square feet for rooms, lawns and lots. Choose a shape, or add up to four rectangles for L-shaped and irregular spaces, then see the total in sq ft, sq yd, sq m and acres.

**Quick answer:** To find square footage, multiply length by width in feet: a 12 × 15 ft room is 180 square feet. For a circle use π × radius², for a triangle ½ × base × height. One square yard is 9 square feet and one acre is 43,560 square feet.

_Last updated: October 4, 2026. Estimates only; confirm quantities with your supplier._

## How to calculate square footage

Square footage is the area of a flat surface measured in square feet. For any rectangular room or lot, **multiply length by width** (both in feet). A 12 ft × 15 ft room is 180 square feet. Other shapes have their own formulas:

| Shape | Formula |
| --- | --- |
| Rectangle / square | length × width |
| Triangle | ½ × base × height |
| Circle | π × (diameter ÷ 2)² — about 0.785 × diameter² |
| Trapezoid | ½ × (side A + side B) × height |
| Parallelogram | base × perpendicular height |
| Ellipse / oval | π × (width ÷ 2) × (height ÷ 2) |
| Circle sector | π × radius² × angle ÷ 360 |

### How to measure an L-shaped or irregular space

Split the space into rectangles, measure each, and add the areas. Choose *Several rectangles* above and enter up to four sections. For a whole house, list each room separately and add them. Subtract anything that isn't part of the surface — a kitchen island, a fireplace hearth, or a patio inside a lawn.

### Worked example: an L-shaped living and dining area

Split the space into two rectangles: the living room is 18 × 12 ft = 216 sq ft and the dining nook is 10 × 8 ft = 80 sq ft, so the total is **296 sq ft** (32.9 sq yd). Flooring with 7% waste means buying about 317 sq ft; at $3.50 per square foot that is roughly $1,109 in material.

### Common room sizes in square feet

| Room size | Square feet | Square yards |
| --- | --- | --- |
| 10 × 10 ft | 100 | 11.1 |
| 10 × 12 ft | 120 | 13.3 |
| 12 × 12 ft | 144 | 16.0 |
| 12 × 15 ft | 180 | 20.0 |
| 12 × 20 ft | 240 | 26.7 |
| 14 × 16 ft | 224 | 24.9 |
| 15 × 20 ft | 300 | 33.3 |
| 20 × 20 ft | 400 | 44.4 |
| 20 × 30 ft | 600 | 66.7 |

### Unit conversions

| From | To |
| --- | --- |
| 1 square yard | 9 square feet |
| 1 square meter | 10.764 square feet |
| 1 acre | 43,560 square feet |
| 1 square foot | 144 square inches |

### What square footage is used for

Flooring, tile, paint, sod, roofing, insulation and carpet are all bought by area. Once you have the square footage, add a waste allowance (typically 5–10%) and use the right calculator: [flooring](../flooring-calculator/), [paint](../paint-calculator/), [tile](../tile-calculator/), [carpet](../carpet-calculator/) or [sod](../sod-calculator/). Real-estate listings often quote *gross living area*, which counts finished, heated space only and excludes garages, porches and unfinished basements.

### Area formulas for common shapes

| Shape | Formula | Example | Area |
| --- | --- | --- | --- |
| Rectangle | length × width | 12 × 15 ft | 180.0 sq ft |
| Triangle | ½ × base × height | base 10, height 6 ft | 30.0 sq ft |
| Circle | π × radius² | diameter 12 ft | 113.1 sq ft |
| Trapezoid | ½ × (a + b) × height | a 8, b 12, height 6 ft | 60.0 sq ft |
| Half circle | ½ × π × radius² | diameter 12 ft | 56.5 sq ft |

### Square feet in other units

| Square feet | Square yards | Square meters | Acres |
| --- | --- | --- | --- |
| 100 | 11.1 | 9.3 | 0.002 |
| 500 | 55.6 | 46.5 | 0.011 |
| 1,000 | 111.1 | 92.9 | 0.023 |
| 5,000 | 555.6 | 464.5 | 0.115 |
| 43,560 | 4840.0 | 4046.9 | 1.000 |

One square yard is 9 square feet, and one acre is 43,560 square feet. Use the same area with the [flooring](../flooring-calculator/), [paint](../paint-calculator/), [tile](../tile-calculator/) or [sod](../sod-calculator/) calculators to turn it into a shopping list.

### Measuring mistakes to avoid

- **Mixing units.** Convert inches to feet (divide by 12) before multiplying.
- **Using outside dimensions.** For flooring and paint, measure the finished inside of the room.
- **Forgetting alcoves and closets.** Measure them as separate rectangles and add them.
- **Not subtracting what is not covered.** Built-ins, tubs and openings reduce the area for flooring and wall materials.
- **Forgetting waste.** Area is the net figure; most materials need extra for cuts.

## Frequently asked questions

### How do I calculate square feet of a room?

Measure the room's length and width in feet and multiply. A 12 ft × 15 ft room is 180 square feet.

### How do I calculate square footage of an L-shaped room?

Divide it into two rectangles, find the area of each, and add them together. The calculator above lets you enter up to four sections.

### How many square feet are in a square yard?

9 square feet. Carpet is sold by the square yard, so divide square feet by 9.

### How do I convert square inches to square feet?

Divide by 144, since a square foot contains 12 × 12 = 144 square inches.

### How many square feet are in an acre?

One acre is 43,560 square feet — roughly a football field without the end zones.

### How do I find the square footage of a circle?

Square the radius (half the diameter) and multiply by 3.1416. A circle 10 feet across has about 78.5 square feet.

### How do I calculate square footage in meters?

Choose Meters in the unit menu. One square meter is 10.764 square feet.

### Does square footage include walls?

For a room, measure wall to wall (inside dimensions) for flooring and paint calculations. Listings may use outside measurements, so they can be slightly larger.

## Sources and further reading

- [NIST Special Publication 811: conversion factors](https://www.nist.gov/pml/special-publication-811/nist-guide-si-appendix-b-conversion-factors) — National Institute of Standards and Technology