Convert acres to square miles easily.

If you’ve ever driven through rural America or browsed real estate listings, you’ve probably seen land measured in acres. But when you’re dealing with massive areas like national parks or agricultural regions, square miles become the go-to unit. Converting between these two isn’t just about math, it’s about understanding how we visualize space. Let’s break it down in a way that’s as easy as splitting a pie (or maybe a section of farmland).

Unit definitions

What is a acre (ac)?

An acre is a unit of area primarily used in the US customary and imperial systems. It’s traditionally defined as the area of one chain by one furlong (66 feet by 660 feet), totaling 43,560 square feet. Symbol: ac. Common uses include measuring plots of land, agricultural fields, and real estate parcels. Fun fact, the word "acre" comes from Old English "æcer," meaning "open field."

What is a square mile (mi²)?

A square mile represents an area equal to a square measuring one mile on each side. Symbol: mi². It’s used for larger territories like cities, counties, or natural landmarks. One square mile contains 640 acres, a number that’s remained consistent since the 16th century. You’ll often see it in geographical surveys and infrastructure planning.

Conversion formula

To convert acres to square miles, divide the number of acres by 640:

square miles = acres ÷ 640

For square miles to acres, multiply by 640:

acres = square miles × 640

Example calculations

1. Converting 320 acres to square miles:
   320 ÷ 640 = 0.5 mi²
   (That’s half of a square mile, roughly the size of Central Park).
2. Converting 2.5 square miles to acres:
   2.5 × 640 = 1,600 acres
   (Equivalent to about 1,210 football fields).

Conversion tables

Acres to square miles

Square miles to acres

From medieval fields to modern cities

The acre’s history is rooted in agriculture. Medieval farmers needed a practical way to measure land that oxen could plow in a day. This 'acre” became standardized over time, though its exact size varied regionally until the 14th century. The square mile gained prominence during British imperial expansion, providing a standardized way to map colonies. Today, these units coexist in zoning laws and property deeds. For instance, when Texas joined the US, its public lands were surveyed using square miles but sold in acre parcels to settlers. This dual system continues to benifit various industries, from urban planning to ranching.

Interesting facts

1. Manhattan Island is about 22.8 square miles (14,592 acres)
2. The phrase “40 acres and a mule” references 1865’s unfulfilled land redistribution promise
3. Rhode Island, the smallest US state, covers 776,900 acres (1,214 square miles)
4. Disney World occupies 27,000 acres (42.2 square miles)
5. One square mile of land can hold approximately 640 average-sized US homes

FAQ