Acre — Definition, Formula & Examples

An acre is a unit of area used to measure land, equal to 43,560 square feet. It is roughly the size of a football field without the end zones.

An acre is a US customary and imperial unit of area defined as exactly 43,560 square feet, equivalent to 4,840 square yards or approximately 4,047 square meters.

Key Formula

A = \frac{\text{area in square feet}}{43{,}560}

Where:

$A$ = Area measured in acres

How It Works

Acres measure flat land area, not length or width. A square plot that is 1 acre has sides of about 208.7 feet. To convert square feet to acres, divide by 43,560. To convert acres to square feet, multiply by 43,560. Acres are commonly used in real estate listings, farming, and land surveying across the United States.

Worked Example

Problem: A rectangular field is 330 feet long and 660 feet wide. How many acres is it?

Find the area in square feet: Multiply the length by the width.

330 \times 660 = 217{,}800 \text{ ft}^2

Convert to acres: Divide the area in square feet by 43,560.

\frac{217{,}800}{43{,}560} = 5 \text{ acres}

Answer: The field is 5 acres.

Why It Matters

Acres appear in everyday life whenever land is bought, sold, or described. Understanding acres helps you compare property sizes in real estate ads and grasp the scale of farms, parks, and nature reserves.

Common Mistakes

Mistake: Thinking an acre has a fixed shape, like a square.

Correction: An acre is purely an amount of area (43,560 sq ft). It can be any shape — a long rectangle, an irregular polygon, or a square.