Acres to Square Miles Converter - Convert acres to mi² (Exact: 1 acre = 0.0015625 mi²)
Accurate acres to square miles (mi²) converter using exact US customary definitions: 1 mi² = 640 acres ⇒ 1 acre = 0.0015625 mi². Ideal for land planning, agriculture, forestry, conservation, appraisal, and GIS reporting. Includes exact formulas, worked examples, expanded tables, rounding guidance, detailed FAQs, and practical tips.
Exact factor: 1 acre = 0.0015625 mi² ⇒ mi² = acres ÷ 640. See all free land area converters.
About Acres to Square Miles Conversion
The acre (ac) is the everyday unit for U.S. parcels, farm fields, and timber stands, while the square mile (mi²) is natural for county or watershed scale summaries. Converting acres to mi² keeps parcel-level detail readable and enables regional reporting without losing fidelity. Because the relationship 1 mi² = 640 acres is exact, you can move between units confidently across GIS, spreadsheets, and BI dashboards.
A robust data strategy stores canonical area in m², derives acres for familiar U.S. presentations, and provides mi² for regional summaries-all rounded once at presentation. This avoids double rounding and ensures PDFs, emails, and CSV exports stay synchronized with your map outputs.
Typical workflows include translating multi-parcel holdings into a single mi² figure for executive summaries, reconciling legacy acre-based datasets with modern SI analytics, and publishing side-by-side acres/mi² metrics for public communications.
Acres to Square Miles Formula
Exact relationship
Use either expression:
mi² = acres ÷ 640
// exact identity
1 acre = 0.0015625 mi²
// inverse
acres = mi² × 640Example:
800 acres ÷ 640 = 1.25 mi²Related Area Converters
What is an Acre (ac)?
The international acre is defined as exactly 4,046.8564224 m². It is ubiquitous in U.S. real estate listings, agricultural planning, and state and county datasets. Communicating results in acres makes scale intuitive for local stakeholders while keeping your canonical store in m² preserves global compatibility.
What is a Square Mile (mi²)?
A square mile is the area of a square one mile on each side. Reconciling via SI, 1 mi² = (1609.344 m)² = 2,589,988.110336 m². The square mile is ideal for regional summaries-watersheds, counties, management units-where acre totals become large numbers.
Step-by-Step: Converting acres to mi²
- Read the area in acres (ac) from your listing, map, or report.
- Divide by 640 (or multiply by 0.0015625) to convert to square miles (mi²).
- Round once at presentation (e.g., 2–3 decimals for dashboards; more for technical annexes if required).
Example walkthrough:
Input: 240 acres
Compute: 240 ÷ 640 = 0.375 mi²
Output: 0.375 mi² (UI policy: 3 decimals; keep full precision internally)Common Conversions
Everyday quick checks (ac → mi²)
| acres | mi² | acres | mi² |
|---|---|---|---|
| 64 | 0.1 | 1,600 | 2.5 |
| 160 | 0.25 | 3,200 | 5.0 |
| 320 | 0.5 | 6,400 | 10.0 |
| 640 | 1.0 | 16,000 | 25.0 |
| 800 | 1.25 | 25,600 | 40.0 |
Quick Reference Table
Square miles to acres (mi² → ac)
| mi² | acres | mi² | acres |
|---|---|---|---|
| 0.10 | 64 | 2.50 | 1,600 |
| 0.25 | 160 | 5.00 | 3,200 |
| 0.50 | 320 | 10.00 | 6,400 |
| 0.75 | 480 | 25.00 | 16,000 |
| 1.00 | 640 | 40.00 | 25,600 |
Precision, Rounding & Significant Figures
Operational rounding
For public dashboards, 2–3 decimals in mi² are easy to read; for legal filings or survey annexes, match your measurement uncertainty and governing standard. Always compute with full precision and round once on output to keep maps, PDFs, and exports synchronized.
Consistent documentation
Standardize field names (e.g., area_m2, area_mi2, area_ac, area_ha) and include a concise methods note: “Exact constants; 1 mi² = 640 acres; 1 acre = 0.0015625 mi²; round once at presentation.” Consistency prevents subtle discrepancies during audits and reconciliations.
Where This Converter Is Used
- 🌾 Agriculture: Translating parcel totals from acres into regional mi² summaries for grants and planning.
- 🌳 Forestry & conservation: Converting timber stands and habitat units to mi² for cross-jurisdiction reporting.
- 🏞️ Parks & recreation: Publishing park inventories and master plans in both acres and mi² for clarity.
- 🏡 Real estate & appraisal: Aggregating multiple acre-based parcels into concise square-mile statements.
- 🛰️ GIS & remote sensing: Rolling up acre-based layers to mi² in executive dashboards and regional KPIs.
Frequently Asked Questions
What is the exact formula to convert acres to square miles?
By definition, 1 square mile equals exactly 640 acres. Therefore 1 acre = 1 ÷ 640 mi² = 0.0015625 mi² (exact). In general: mi² = acres ÷ 640. The inverse operation uses acres = mi² × 640. Because these are definitional identities, your results are deterministic and audit-friendly.
Does the international vs. U.S. survey foot affect this conversion?
No for the unit *ratio*. While historical datasets may reference the U.S. survey foot, the relationship 1 mi² = 640 acres is exact in U.S. customary land measure and remains valid. If you reconcile via SI, 1 mi = 1609.344 m and 1 acre = 4046.8564224 m² still evaluate to exactly 640 acres per square mile.
Which unit should I keep as my system’s canonical store?
Use a single canonical unit-most teams choose square meters (m²) for interoperability with SI. Derive acres for U.S.-facing reports and square miles for regional summaries. Rounding once at presentation keeps maps, PDFs, emails, and CSV exports perfectly aligned.
What rounding is appropriate for acres ↔ mi² on public dashboards and filings?
Compute with full precision and round once on output. For public pages, 2–3 decimals in mi² or 0–2 decimals in acres typically read well. For survey or compliance documents, follow the precision dictated by your measurement method and governing standard.
Do map projections change the acres-to-mi² conversion factor?
Projections influence how you compute polygon area from coordinates, but they never change the unit factor. Once you have an area in acres or m², converting to mi² is a pure unit step using the exact 1 mi² = 640 acres identity.
How do acres relate to hectares and square kilometers?
1 hectare (ha) = 10,000 m² ≈ 2.4710538147 acres (exact via m²). 1 square mile ≈ 2.589988110336 km². You can bridge acres ↔ hectares precisely through square meters, and acres ↔ square miles using the exact 640 ratio.
What field names and documentation avoid unit mistakes across teams?
Use explicit, unit-suffixed fields such as area_m2, area_mi2, area_ac, and area_ha. Include a short methods note: “Exact constants: 1 mi² = 640 acres; 1 acre = 0.0015625 mi²; round once at presentation.” This prevents double-rounding and off-by-factor errors in multi-system pipelines.
What anchor pairs help me sanity-check conversions quickly?
Memorize: 100 acres = 0.15625 mi²; 160 acres = 0.25 mi²; 320 acres = 0.5 mi²; 640 acres = 1 mi²; 1,600 acres = 2.5 mi². These are great for regression tests in both directions.
Tips for Working with acres & mi²
- Keep m² canonical; derive acres, mi², ha, and km² for UI and exports.
- Round once at presentation; avoid re-rounding during CSV/PDF generation.
- Use explicit unit columns and publish constants in your methods note to prevent conversion drift.
- Maintain regression pairs (e.g., 800 ac ↔ 1.25 mi²; 100 ac ↔ 0.15625 mi²) and test both directions in CI.