# Acres to Square Miles Converter URL: https://speedycalculator.com/calculators/conversion/acres-to-square-miles/ Last updated: 2026-10-25 > Convert acres (acre) to square miles (mi²): 1 acre = 0.0015625 mi², so multiply by 0.0015625 or divide by 640. Both fields are editable, so you can also type in square miles and get acres back. ## Inputs - Acres (acre) ## Results - Square miles ## Formula ``` 1 acre = 0.0015625 mi² 1 mi² = 640 acre mi² = acre × 0.0015625 ``` ## Explanation A square mile contains exactly 640 acres. U.S. land surveys (the Public Land Survey System) divide land into one-square-mile sections of 640 acres. ### How to use the Acres to Square Miles Converter - Type the number of acres into the **Acres** field. Decimals such as 320 are fine. - Read the answer in **Square miles** – it updates as you type, with no button to press. - To convert the other way, type into **Square miles** and the acres are recalculated. - Press **Copy results** to copy both values with the page title, or **Copy link** to share this exact conversion. This page converts only acre ⇄ mi². Need a different unit? Use the general area converter, where you can choose any “from” and “to” unit. ### How it works Both units measure area, so they are always in the same ratio: one acre equals 0.0015625 square miles. The calculator multiplies the number of acres you type by 0.0015625 to give square miles, and when you type into the square miles field it divides by the same factor to give acres. Because the ratio never changes, doubling the acres always doubles the square miles. Results are calculated at full precision and rounded only for display (up to eight decimal places, with very large or small values shown in scientific notation). ### How to convert acres to square miles - Write down the value in acres, for example **640 acre**. - Multiply by the conversion factor 0.0015625 (because 1 acre = 0.0015625 mi²). - 640 × 0.0015625 = **1 mi²**. - To go back from square miles to acres, divide by 0.0015625 – or multiply by 640. ### acre to mi² conversion table AcresSquare milesSquare milesAcres1 acre0.0015625 mi²1 mi²640 acre10 acre0.015625 mi²2 mi²1,280 acre40 acre0.0625 mi²5 mi²3,200 acre160 acre0.25 mi²10 mi²6,400 acre320 acre0.5 mi²20 mi²12,800 acre640 acre1 mi²50 mi²32,000 acre1,000 acre1.5625 mi²100 mi²64,000 acre5,000 acre7.8125 mi²1,000 mi²640,000 acre10,000 acre15.625 mi² ### What is an acre? An acre is exactly 43,560 square feet, about 4,047 m². Historically it was the land a team of oxen could plough in a day. It remains the land unit in the U.S. and UK. ### What is a square mile? A square mile is 640 acres, about 2.59 km². U.S. land surveys divide land into one-square-mile sections, and U.S. state and county areas are given in square miles. ### Quick mental conversion For a fast estimate, multiply acres by about **0.0016** to get square miles; the error is about 2.4%. Use the calculator above when you need the exact figure. ### Common mistakes to avoid Converting area with a length factor (1 m = 3.28 ft, but 1 m² = 10.76 ft², not 3.28 ft²), and assuming regional land units such as marla, bigha or katha have one standard size everywhere. ## Worked example Inputs — Acres: 640 acre. Results — **Square miles = 1 mi²**. ## FAQ **How many acres in a square mile?** 640. **How many square miles is 1,000 acres?** 1.5625 mi². **How do I convert acres to square miles?** Multiply the number of acres by 0.0015625. For example, 640 acre × 0.0015625 = 1 mi². **How do I convert square miles back to acres?** Divide by 0.0015625 (or multiply by 640), or simply type the value into the square miles field above. **What is 10 acre in square miles?** 10 acre = 0.015625 mi². **What is 1,000 acre in square miles?** 1,000 acre = 1.5625 mi². **Is this conversion exact?** Yes. The factor comes from the official definitions of both units (NIST and the SI), so the only difference you may see is rounding in the last displayed digit. **Can I convert to other units on this page?** This page converts only between acres and square miles. To pick any area unit, use the general area converter linked under Related calculators. **What formula does the Acres to Square Miles Converter use?** 1 acre = 0.0015625 mi². ## Sources - [NIST Special Publication 811 – Guide for the Use of the International System of Units](https://www.nist.gov/pml/special-publication-811) - [NIST Handbook 44 Appendix C – General tables of units of measurement](https://www.nist.gov/pml/owm/nist-handbook-44-current-edition)