Square Miles to Acres Converter

Welcome to our Square Miles to Acres Converter, a comprehensive tool for converting between two of the most important land area measurements in the United States. Whether you are a real estate professional, farmer, land surveyor, student, or anyone working with land measurements, this converter provides instant results with step-by-step calculations and real-world size comparisons.

The Conversion Factor: 640 Acres per Square Mile

The fundamental relationship between square miles and acres is elegantly simple:

This means:

• Square Miles to Acres: Multiply by 640
• Acres to Square Miles: Divide by 640

Where Does 640 Come From?

The 640-acre square mile comes from basic geometry combined with how acres were historically defined:

• 1 mile = 5,280 feet
• 1 square mile = 5,280 × 5,280 = 27,878,400 square feet
• 1 acre = 43,560 square feet (originally the amount of land a yoke of oxen could plow in a day)
• 27,878,400 ÷ 43,560 = exactly 640 acres

Quick Reference Conversion Table

Understanding the Section System

The relationship between square miles and acres is foundational to the US Public Land Survey System (PLSS), established in 1785 to systematically divide and distribute western lands:

• Section: 1 square mile = 640 acres - The basic unit of land survey
• Quarter Section: 160 acres - The standard homestead granted under the Homestead Act of 1862
• Township: 36 square miles (6×6 grid of sections) = 23,040 acres

This systematic grid still defines property boundaries across most of the United States west of the original 13 colonies.

Real-World Size Comparisons

What Does a Square Mile Look Like?

One square mile (640 acres) is approximately:

• About the size of Central Park in NYC (0.77 times)
• Roughly 485 American football fields
• About 397 soccer fields (FIFA standard)
• Approximately 256 city blocks in Manhattan

What Does an Acre Look Like?

One acre is approximately:

• 90% of an American football field (including end zones)
• About 16 tennis courts
• Roughly 9 basketball courts
• A square measuring 208.7 × 208.7 feet

Common Applications

Real Estate and Land Sales

Real estate professionals regularly convert between these units. Large properties like ranches and farms are often listed in acres, while regional land statistics use square miles. A 5,000-acre ranch equals about 7.8 square miles.

Agriculture and Farming

Farmers typically measure their land in acres for crop planning, while county agricultural reports often use square miles. Understanding this conversion helps with yield calculations, land valuation, and agricultural planning.

Urban Planning and Development

City planners work with both units. Zoning maps might show square miles, while individual lot sizes are in acres or fractions of acres. A typical suburban subdivision of 100 homes might occupy 50-100 acres (0.08-0.16 square miles).

Environmental and Conservation

Conservation areas, national parks, and wildlife refuges are often measured in both units. For example, Yellowstone National Park covers about 2.2 million acres or 3,472 square miles.

How to Use This Converter

1. Enter your value: Type the number of square miles or acres you want to convert
2. Select direction: Choose whether to convert Square Miles → Acres or Acres → Square Miles
3. Set precision: Adjust decimal places from 0 to 10 based on your needs
4. Click Convert: Get instant results with step-by-step calculations and size comparisons

Frequently Asked Questions

How many acres are in a square mile?

There are exactly 640 acres in one square mile. This relationship comes from the US Public Land Survey System established in 1785, where a square mile (called a "section") was divided into 640 one-acre parcels for land distribution.

How do I convert square miles to acres?

To convert square miles to acres, multiply the number of square miles by 640. For example, 2.5 square miles × 640 = 1,600 acres. The formula is: Acres = Square Miles × 640.

How do I convert acres to square miles?

To convert acres to square miles, divide the number of acres by 640. For example, 1,280 acres ÷ 640 = 2 square miles. The formula is: Square Miles = Acres ÷ 640.

Why are there exactly 640 acres in a square mile?

There are 640 acres in a square mile because: 1 mile = 5,280 feet, so 1 square mile = 5,280 × 5,280 = 27,878,400 square feet. Since 1 acre = 43,560 square feet, dividing gives us 27,878,400 ÷ 43,560 = 640 acres exactly.

What is a section of land?

A section of land is a unit of area in the US Public Land Survey System equal to exactly 1 square mile or 640 acres. Sections are identified by number within a township. A quarter section (160 acres) was the standard homestead size given to settlers under the Homestead Act of 1862.

How big is an acre visually?

An acre is about 90% the size of an American football field (including end zones). It equals approximately 43,560 square feet, or about 208.7 feet × 208.7 feet if square. Visually, it is roughly the size of 16 tennis courts or 9 basketball courts.

Related Conversions

Our converter also shows additional unit equivalents including:

• Square Kilometers (km²): 1 sq mi = 2.58999 km²
• Hectares (ha): 1 acre = 0.404686 hectares
• Square Feet (ft²): 1 acre = 43,560 sq ft
• Square Meters (m²): 1 acre = 4,046.86 m²

Related Tools

• Acres to Square Miles Converter
• Acres to Hectares Converter
• Hectares to Acres Converter
• Acres to Square Feet Converter
• Square Feet to Acres Converter

Additional Resources

• Square Mile - Wikipedia
• Acre - Wikipedia
• US Public Land Survey System - Wikipedia