Square Miles to Hectares Converter - Convert mi² to ha (Exact via SI: 1 mi² = 258.9988110336 ha)
Accurate square miles (mi²) to hectares (ha) converter via SI: 1 mi² = 2,589,988.110336 m² ⇒ 1 mi² = 258.9988110336 ha. Purpose-built for land planning, agriculture, forestry, conservation, appraisal, and GIS reporting. Includes exact formulas, worked examples, expanded tables, rounding guidance, detailed FAQs, and practical tips.
SI-derived factor: 1 mi² = 258.9988110336 ha ⇒ ha = mi² × 258.9988110336. See all free area unit converters.
About Square Miles to Hectares Conversion
The square mile (mi²) is natural for regional reporting-counties, watersheds, and management units-while the hectare (ha) is the global metric standard for agriculture, forestry, conservation, and land administration. Converting mi² to ha helps align U.S.-oriented summaries with SI-first analytics, regulatory filings, and international communications.
Best practice is to keep your canonical store in square meters (m²) or hectares (ha), derive mi² and acres for stakeholder-facing outputs, and round once at presentation. This avoids double rounding and keeps maps, dashboards, PDFs, and CSV exports synchronized end to end.
Typical workflows include rolling up conservation areas and county-scale studies from mi² to ha for grant reporting, reconciling legacy imperial datasets with SI models, and offering dual-unit tables that remain audit-friendly thanks to explicit constants.
Square Miles to Hectares Formula
Exact relationship (via SI)
Use either expression:
ha = mi² × 258.9988110336
// inverse
mi² = ha × 0.003861021585424458Example:
2.5 mi² × 258.9988110336 = 647.497027584 haRelated Area Converters
What is a Square Mile (mi²)?
A square mile is the area of a square one mile on a side. In SI terms, 1 mi² = 2,589,988.110336 m². It condenses very large acre counts (640 acres per mi²) into digestible regional figures for policy and executive communications.
What is a Hectare (ha)?
A hectare equals exactly 10,000 m²-a 100 m × 100 m square. It’s the SI land unit of choice for farms, forests, parks, and official land records, and it integrates smoothly with GIS workflows that compute areas in square meters.
Step-by-Step: Converting mi² to ha
- Read the area in square miles (mi²) from your map, model, or report.
- Multiply by 258.9988110336 to convert to hectares (ha).
- Round once at presentation (e.g., 0–2 decimals for large regions; more for small sites if justified).
Example walkthrough:
Input: 0.75 mi²
Compute: 0.75 × 258.9988110336 = 194.2491082752 ha
Output: 194.2491 ha (UI policy: 4 decimals; retain full precision internally)Common Conversions
Everyday quick checks (mi² → ha)
| mi² | ha | mi² | ha |
|---|---|---|---|
| 0.10 | 25.89988110336 | 2.50 | 647.497027584 |
| 0.25 | 64.7497027584 | 5.00 | 1,294.994055168 |
| 0.50 | 129.4994055168 | 10.00 | 2,589.988110336 |
| 1.00 | 258.9988110336 | 20.00 | 5,179.976220672 |
Quick Reference Table
Hectares to square miles (ha → mi²)
| ha | mi² | ha | mi² |
|---|---|---|---|
| 10 | 0.03861021585 | 200 | 0.7722043171 |
| 25 | 0.09652553964 | 500 | 1.9305107927 |
| 50 | 0.1930510793 | 1,000 | 3.861021585 |
| 100 | 0.3861021585 | 2,500 | 9.652553964 |
Precision, Rounding & Significant Figures
Operational rounding
For public dashboards, 0–2 decimals in hectares are easy to read for large geographies; for smaller sites, 2–4 decimals can be helpful. Always compute with full precision and round once at output to keep maps, PDFs, and exports synchronized.
Consistent documentation
Standardize field names (e.g., area_m2, area_ha, area_mi2, area_ac) and publish a concise methods note: “SI-derived constants; 1 mi² = 258.9988110336 ha; round once at presentation.” This prevents off-by-factor mistakes and audit drift.
Where This Converter Is Used
- 🌳 Forestry & conservation: Converting regional management units from mi² into ha for cross-jurisdiction reporting.
- 🌾 Agriculture: Rolling up production zones and farm blocks for international funding and benchmarks.
- 🏙️ Urban & regional planning: Expressing counties or districts in ha to align with SI policies and international partners.
- 🏞️ Parks & recreation: Publishing master plans with dual-unit tables (mi²/ha) for public and technical audiences.
- 🛰️ GIS & remote sensing: Keeping canonical m²/ha while providing mi² summaries for executive dashboards.
Frequently Asked Questions
What is the exact formula to convert square miles to hectares?
Use ha = mi² × 258.9988110336. This comes from the exact SI relationship 1 mi² = 2,589,988.110336 m² and 1 hectare = 10,000 m². Dividing gives 2,589,988.110336 ÷ 10,000 = 258.9988110336 ha per mi².
How many hectares are 0.1, 1, and 10 square miles?
0.1 mi² = 25.89988110336 ha; 1 mi² = 258.9988110336 ha; 10 mi² = 2,589.988110336 ha. For public-facing summaries, 2–3 decimals usually read well; keep full precision internally.
What is the reverse conversion from hectares to square miles?
Use mi² = ha × (10,000 ÷ 2,589,988.110336) ≈ ha × 0.003861021585424458. Both directions reconcile exactly through SI when computed with sufficient precision.
Does the choice of map projection change the mi² → ha factor?
No. Map projections affect how area is measured from coordinates, but once an area is obtained in mi² (or m²), converting to ha is a pure unit conversion with a fixed factor.
Which area unit should I store canonically?
Most teams store square meters (m²) or hectares (ha) for SI interoperability. Derive mi² and acres for regional and U.S.-facing outputs. Always compute with full precision and round once at presentation.
How should I round mi² ↔ ha for dashboards and filings?
Compute with full precision and round once on output. For hectares, 0–2 decimals are typical for larger regions and 2–4 for smaller sites. Follow any precision mandated by measurement methods or regulation.
Any good mental approximations for quick checks?
Yes-multiply mi² by ~259 to get ha. For example, 2.5 mi² ≈ 2.5 × 259 ≈ 648 ha (exact: 647.497027584 ha). Use approximations for sanity checks, not deliverables.
How do hectares relate to acres and square kilometers?
1 ha = 10,000 m²; 1 km² = 100 ha; 1 ha ≈ 2.4710538147 acres. You can bridge mi² ↔ ha via m² or mi² ↔ acres (1 mi² = 640 acres) and then acres ↔ ha; both paths agree when computed precisely.
What field names and documentation avoid unit mistakes across teams?
Use explicit, unit-suffixed fields (area_m2, area_ha, area_mi2, area_ac). Publish a short methods note with constants (e.g., “1 mi² = 258.9988110336 ha; round once at presentation”). Add bidirectional unit tests in CI.
Why is the factor shown with many decimals?
Because it’s derived from an exact SI identity that doesn’t produce a short terminating decimal in base-10 for the inverse. Keep full precision internally; round only at display.
What pitfalls appear in legacy spreadsheets and GIS layers?
Avoid converting already-rounded values. Convert from the canonical store (m²/ha), document constants and rounding, and verify representative anchors (e.g., 1 mi² ↔ 258.9988110336 ha) in both directions.
Tips for Working with mi² & ha
- Keep m²/ha canonical; derive mi², acres, and ft² for UI and exports.
- Round once at presentation; document precision by context (e.g., 2 decimals for regional rollups).
- Publish constants and keep bidirectional tests (e.g., 2.5 mi² ↔ 647.497027584 ha) to catch regressions.
- Avoid converting already-rounded values; always convert from the canonical store.