Square Miles to Square Feet Calculator
Convert square miles to square feet: 1 sq mi = 5,280² = 27,878,400 sq ft, exactly, and = 640 acres. Type either box — it runs both ways.
Last updated:Conversion Formula
Conversion factors follow NIST Special Publication 811, Appendix B.9.1 (area), and the BLM Public Land Survey System study guide. Links are in Sources below.
square feet = square miles × 27,878,400
square miles = square feet ÷ 27,878,400 (1 sq ft = 3.587006427915519 × 10⁻⁸ sq mi)
Both routes are definitional and exact: 5,280 × 5,280 = 27,878,400, and 640 acres × 43,560 sq ft = 27,878,400. One square mile also equals 3,097,600 sq yd, 4,014,489,600 sq in, 258.9988110336 hectares and 2.589988110336 km².
Worked Example
A deed reads NE1/4SW1/4SE1/4 of Section 12. How many square feet is that?
- Read the aliquot parts from the smallest outward: SE1/4 of a section is 160 acres; SW1/4 of that is 40 acres; NE1/4 of that is 10 acres. The BLM study guide uses this exact description and gives 10 acres.
- In square miles: 10 ÷ 640 = 0.015625 sq mi.
- Convert: 0.015625 × 27,878,400 = 435,600 sq ft.
- Cross-check by acres: 10 × 43,560 = 435,600 sq ft. ✓ Same answer, as it must be, because 640 × 43,560 = 27,878,400.
Note the punctuation rule from the same guide: a comma means "AND THE" and no comma means "OF THE". NE1/4, SW1/4, SE1/4 is three separate quarter-sections totalling 480 acres; NE1/4SW1/4SE1/4 is one 10-acre parcel nested inside itself. Same characters, 48× the land.
Quick Reference
| Square Miles | Square Feet |
|---|---|
| 0.0015625 sq mi (1 acre) | 43,560 |
| 0.01 sq mi | 278,784 |
| 0.015625 sq mi (10 acres) | 435,600 |
| 0.0625 sq mi (40 acres, a forty) | 1,742,400 |
| 0.1 sq mi | 2,787,840 |
| 0.25 sq mi (160 acres, quarter-section) | 6,969,600 |
| 0.5 sq mi (320 acres) | 13,939,200 |
| 1 sq mi (640 acres, 1 section) | 27,878,400 |
| 2 sq mi | 55,756,800 |
| 5 sq mi | 139,392,000 |
| 10 sq mi | 278,784,000 |
| 36 sq mi (1 township) | 1,003,622,400 |
| 100 sq mi | 2,787,840,000 |
One square mile in every unit on this site
| Square miles | Square feet | Acres | Hectares |
|---|---|---|---|
| 0.0015625 | 43,560 | 1 | 0.40468564224 |
| 0.015625 | 435,600 | 10 | 4.0468564224 |
| 0.0625 | 1,742,400 | 40 | 16.1874256896 |
| 0.25 | 6,969,600 | 160 | 64.7497027584 |
| 1 | 27,878,400 | 640 | 258.9988110336 |
| 36 | 1,003,622,400 | 23,040 | 9,323.9571972096 |
| 0.386102158542 | 10,763,910.4167 | 247.1053814672 | 100 |
The last row is 1 km² expressed in imperial units: 1 km² = 1,000,000 m² ÷ 0.09290304 = 10,763,910.4167 sq ft = 100 ha = 1,000,000 ÷ 2,589,988.110336 = 0.386102158542 sq mi. Square yards and inches: 1 sq mi = 3,097,600 sq yd = 4,014,489,600 sq in.
What is a square mile?
A square mile is the area of a square one mile on each side. The mile is exact: 1 mi = 5,280 ft = 1,760 yd = 80 chains = 8 furlongs = 1,609.344 m. The last figure follows from 1 ft = 0.3048 m exactly, so 5,280 × 0.3048 = 1,609.344 m and 1,609.344² = 2,589,988.110336 m².
NIST SP 811 prints that as 2.589 988 E+06 m² and 2.589 988 E+00 km², both rounded to seven significant figures. It also carries a second row, square mile (based on U.S. survey foot) = 2.589 998 E+06 m². See the section below for why two rows exist and when the difference matters.
In the Public Land Survey System, a square mile is a section, and the BLM study guide states it directly: "One square mile equates to 640 acres or 80 chains by 80 chains." A township is a 6 × 6 grid of sections, so 36 sections and nominally 36 sq mi.
What is a square foot?
A square foot is the area of a square one foot on each side: 12 in × 12 in = 144 sq in, or 0.09290304 m² exactly (NIST prints 9.290 304 E−02 m²). It is the unit US listings, plats and material orders use, which is why a section-scale figure has to be scaled all the way down before it can be priced per square foot.
Check the chain: 27,878,400 sq ft × 0.09290304 m² per sq ft = 2,589,988.110336 m², which is 1,609.344². Two independent routes to the same number is the whole reason this page can call its factor exact.
What shape is a square mile?
| Shape | Dimensions | Check |
|---|---|---|
| Square in feet (the definition) | 5,280 ft × 5,280 ft | 5,280² = 27,878,400 |
| Square in chains | 80 chains × 80 chains | 6,400 sq chains = 640 acres |
| Square in yards | 1,760 yd × 1,760 yd | 1,760² = 3,097,600 sq yd |
| Square in metres | 1,609.344 m × 1,609.344 m | 1,609.344² = 2,589,988.110336 m² |
| Square in kilometres | 1.609344 km × 1.609344 km | = 2.589988110336 km² |
| Classic section rectangle | 5,280 ft × 5,280 ft, walked as 80 chains | 1 chain = 66 ft, 80 × 66 = 5,280 |
| Circle of the same area | diameter 5,957.84 ft (1.8159 km) | √(1 sq mi × 4 ÷ π) = 0.5641896 mi |
| Township square | 31,680 ft × 31,680 ft | 6 × 5,280 = 31,680; 36 sections |
Walking the boundary of a square-mile section is 4 × 5,280 = 21,120 ft = exactly 4 miles. A township boundary is 24 miles of walking. Fencing a section is therefore quoted per mile of fence line, not per square foot — 27,878,400 sq ft of area tells you nothing about the 4 miles of perimeter until you know the shape.
Nominal sections, convergence, and lots
27,878,400 sq ft is the nominal area of a section. A real section often is not that, and the reason is geometry, not sloppiness.
- Range lines converge. The BLM guide: "As a surveyor works north from the initial point, range lines do not continue in a straight line because of the curvature of the Earth's surface. If not corrected, the township on the baseline would contain more area than one further north."
- Corrections every 24 miles. "To correct for this convergence, surveyors establish guide meridians and standard parallels every 24 miles in each direction from the initial point." Those 24-mile correction lines are why a township grid resets instead of drifting indefinitely.
- The slack lands in lots. "To compensate for loss in acreage to the convergence a land unit called lots was created. Lotting usually occurs in the north and west of each township."
- So sections are not all 640 acres. "For various reasons, not all sections contain 640 acres… The sections along the north tier and the west range of a regular township are often irregular sections and contain lots."
Practical consequence: use 27,878,400 sq ft for arithmetic, planning and unit conversion. For a specific parcel, use the acreage printed on its own plat — an irregular section's lots are described by lot number precisely because their area is not an aliquot fraction of 640.
Two square-mile factors in NIST
NIST SP 811 Appendix B.9.1 lists the square mile twice, with different metric values:
| NIST row | To m² | To km² |
|---|---|---|
| square mile (mi²) | 2.589 988 E+06 | 2.589 988 E+00 |
| square mile (based on U.S. survey foot) | 2.589 998 E+06 | 2.589 998 E+00 |
Both are 27,878,400 sq ft. Nothing about the square-foot count is ambiguous — the disagreement is entirely in how many metres a foot is. The international foot is 0.3048 m exactly; the US survey foot is 1200/3937 m ≈ 0.30480061 m. Over a mile that is a 2 ppm length difference, and because area squares it, about 3.8 ppm in area: roughly 10 m², or about 106 sq ft, per square mile.
The US survey foot was deprecated on December 31, 2022; from January 1, 2023 the international foot supersedes it in all applications (85 FR 62698). Older state-plane data and pre-2023 deeds may still carry survey-foot values, which is the usual reason two authoritative sources disagree in the sixth digit of a km² figure.
FAQ
How many square feet are in one square mile?
Exactly 27,878,400. A mile is 5,280 ft, and area scales by the square of the linear factor, so 5,280 × 5,280 = 27,878,400. The same figure is 640 acres × 43,560 sq ft, or 3,097,600 sq yd, or 4,014,489,600 sq in. It is definitional, not measured, so it never needs rounding.
How many acres are in a square mile, and what is a section?
640 acres exactly. In the Public Land Survey System one square mile is called a section, and the BLM study guide states that one square mile equates to 640 acres or 80 chains by 80 chains. A quarter-section is 160 acres = 0.25 sq mi = 6,969,600 sq ft; a quarter-quarter-section, the traditional forty, is 40 acres = 0.0625 sq mi = 1,742,400 sq ft.
Is every section exactly one square mile?
No. The BLM study guide explains that because range lines converge as a surveyor works north, guide meridians and standard parallels are established every 24 miles, and the resulting excess or deficiency is absorbed in lots that usually fall in the north tier and west range of each township. It states plainly that for various reasons not all sections contain 640 acres. 27,878,400 sq ft is the nominal value; a real section has to be measured from its own plat.
Why does NIST list two different square-mile factors?
NIST SP 811 Appendix B.9.1 prints square mile (mi²) as 2.589 988 E+06 m² and, on a separate row, square mile (based on U.S. survey foot) as 2.589 998 E+06 m². Both are 27,878,400 sq ft; the disagreement is only in the metre value, because a survey foot is 1200/3937 m and an international foot is 0.3048 m. The gap is about 10 m² per square mile, roughly 3.8 parts per million, or about 106 sq ft.
How do I convert square miles to square feet without a calculator?
Multiply by 27,878,400, or use acres as the stepping stone: multiply by 640 to get acres, then by 43,560. For 2.5 sq mi that is 1,600 acres, and 1,600 × 43,560 = 69,696,000 sq ft. The acre route is easier to do in your head and it is exactly equal, because 640 × 43,560 = 27,878,400.
How many square feet are in a township?
Nominally 36 sq mi = 1,003,622,400 sq ft, because a township is a 6 by 6 grid of nominal-mile sections, or 23,040 acres. Treat it as nominal for the same reason as a section: convergence means the surveyed area of a real township differs, and the difference is carried in lots.
Sources and How to Check This Page
- Area factors — square mile 2.589 988 E+06 m², square mile based on the U.S. survey foot 2.589 998 E+06 m², square foot 9.290 304 E−02 m², square yard 8.361 274 E−01 m², square inch 6.4516 E−04 m², acre (based on U.S. survey foot) 4.046 873 E+03 m², hectare 1.0 E+04 m² — are transcribed from NIST Special Publication 811, Appendix B.9.1. Both square-mile rows appear in that table.
- All PLSS quotations in this page — 1 mile = 80 chains, one square mile = 640 acres or 80 chains by 80 chains, township = 6 by 6 nominal mile squares, range-line convergence, guide meridians and standard parallels every 24 miles, lotting in the north and west, not all sections contain 640 acres, and NE1/4SW1/4SE1/4 = 10 acres — come from the BLM Module 2 Public Land Survey System Study Guide, with the chain and acre geometry also on the BLM Land Description Diagram.
- 1 ft = 0.3048 m exactly, the survey foot's 1200/3937 m definition, its deprecation on December 31, 2022, and the 2 parts per million length difference are stated in 85 FR 62698, FR Doc. 2020-21902.
- Every other number here is arithmetic on those factors and can be re-derived: 5,280² = 27,878,400; 640 × 43,560 = 27,878,400; 27,878,400 ÷ 9 = 3,097,600; 27,878,400 × 144 = 4,014,489,600; 5,280 × 0.3048 = 1,609.344 and 1,609.344² = 2,589,988.110336; 27,878,400 × 0.09290304 = 2,589,988.110336; (2,589,998 − 2,589,988.110336) ÷ 2,589,988.110336 = 3.82 × 10⁻⁶ and × 27,878,400 = 106.4; √(4 ÷ π) × 5,280 ÷ 2 = 2,978.92 ft radius; 4 × 5,280 = 21,120; 36 × 27,878,400 = 1,003,622,400; 640 ÷ 4 ÷ 4 ÷ 4 = 10 acres; 1,000,000 ÷ 0.09290304 = 10,763,910.4167 and 1,000,000 ÷ 2,589,988.110336 = 0.386102158542.
- What this page does not claim: the area of any named city, county, park or island. Those are survey or gazetteer figures that need their own citation, and they are almost never an exact number of square miles. This page converts units; it does not measure places.