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Convert Square Feet to Square Miles - Area Converter

This converter transforms area in square feet (ft²) into square miles (mi²) using the defined relationship between feet and miles. It is intended for engineers, GIS professionals, surveyors, planners, and anyone who needs a reliable unit conversion for map work, land area reporting, or calculations.

The unit relationship used here is derived from the defined mile-to-foot relationship: 1 mile = 5,280 feet. Squaring that relationship yields the exact area factor used by the converter. For most practical uses this yields precise and reproducible conversions; read the methodology and FAQs if you work with survey-foot conventions or need legal-grade precision.

Where appropriate, the page references standards and federal resources (NIST, USGS, U.S. Census Bureau) so you can validate definitions and select the correct unit convention for your application.

Updated Nov 7, 2025

Interactive Converter

Convert between square foot and square mile with precision rounding.

Quick reference table

Square FootSquare Mile
1 ft²0 mi²
5 ft²0 mi²
10 ft²0 mi²
25 ft²0 mi²
50 ft²0 mi²
100 ft²0 mi²

Methodology

We use the customary definition 1 mile = 5,280 feet. Squaring both sides gives the exact area relationship: 1 square mile = 5,280² square feet = 27,878,400 ft².

The converter divides the entered square feet value by 27,878,400 to produce square miles. This approach follows standard unit algebra and the definitions used by national measurement authorities.

For extremely large areas or high-precision legal work, be aware of the difference between the International foot (defined exactly as 0.3048 m) and the U.S. survey foot (a slightly different historical definition). See the citations for authoritative guidance.

Worked examples

10,000 ft² = 10,000 ÷ 27,878,400 ≈ 0.000358998 mi²

43,560 ft² (1 acre) = 43,560 ÷ 27,878,400 = 0.0015625 mi² (exactly 1/640 mi²)

1,000,000 ft² = 1,000,000 ÷ 27,878,400 ≈ 0.0358998 mi²

Expert Q&A

What is the exact conversion factor between square feet and square miles?

Exact relationship: 1 square mile = 5,280² square feet = 27,878,400 ft². Therefore, to convert ft² to mi² divide by 27,878,400.

Why might conversion results differ slightly between tools?

Differences usually come from two sources: rounding/precision settings and the foot definition used. Some workflows use the U.S. survey foot (a legacy definition) rather than the International foot. For most applications the International definition (1 ft = 0.3048 m exactly) is used; for cadastral or historical surveying data verify which foot convention was applied.

How many decimal places should I keep?

Choose precision based on measurement uncertainty. For planning maps and general reports 4–6 significant digits is typically sufficient. For legal land descriptions or high-precision GIS analyses retain more digits or use the native data units (meters) and consult a licensed surveyor.

Is this converter suitable for legal or regulatory documents?

This tool provides mathematically exact conversions from the chosen unit definitions, but legal documents often require specific conventions, rounding rules, or certified surveys. For regulatory, cadastral, or title work, confirm the required unit convention and rounding with the responsible agency or a licensed surveyor (see USGS / Census guidance in citations).

What about very large or very small numbers?

You can convert very large or small areas; results may be displayed in scientific notation by some systems. If you plan to store or transfer values between systems, verify numeric field capacity and use appropriate precision to avoid truncation.

How do I convert back from square miles to square feet?

Multiply square miles by 27,878,400 to obtain square feet (ft² = mi² × 27,878,400).

Sources & citations