How many acres are in 1 square mile?

1 mi² equals 640 ac. This is an exact conversion factor defined by NIST.

How do I convert square miles to acres?

Multiply the value in mi² by the conversion factor. For example, 10 mi² = 6400 ac. Use our calculator above for instant results.

Is the square miles to acres conversion exact?

Yes, this conversion is mathematically exact based on the international definition of these units (NIST SP 811).

Can I convert square miles to acres offline?

Yes! OmniConvert runs entirely in your browser — no internet connection needed after the page loads. Your data never leaves your device, ensuring complete privacy.

What is the difference between square miles and acres?

Square Miles (mi²) and Acres (ac) are both units of area but belong to different measurement systems. 1 mi² = 640 ac. Use the converter above to switch between them instantly.

Square Miles to Acres (mi² → ac) — Free Online Converter

mi² → ac Reference Table

mi²	ac
0.001 mi²	0.64 ac
0.002 mi²	1.28 ac
0.003 mi²	1.92 ac
0.004 mi²	2.56 ac
0.005 mi²	3.2 ac
0.006 mi²	3.84 ac
0.007 mi²	4.48 ac
0.008 mi²	5.12 ac
0.009 mi²	5.76 ac
0.01 mi²	6.4 ac
0.02 mi²	12.8 ac
0.03 mi²	19.2 ac
0.04 mi²	25.6 ac
0.05 mi²	32 ac
0.06 mi²	38.4 ac
0.07 mi²	44.8 ac
0.08 mi²	51.2 ac
0.09 mi²	57.6 ac
0.1 mi²	64 ac
0.2 mi²	128 ac
0.3 mi²	192 ac
0.4 mi²	256 ac
0.5 mi²	320 ac
0.6 mi²	384 ac
0.7 mi²	448 ac
0.8 mi²	512 ac
0.9 mi²	576 ac
1 mi²	640 ac
1.5 mi²	960 ac
2 mi²	1280 ac
2.5 mi²	1600 ac
3 mi²	1920 ac
3.5 mi²	2240 ac
4 mi²	2560 ac
4.5 mi²	2880 ac
5 mi²	3200 ac
5.5 mi²	3520 ac
6 mi²	3840 ac
6.5 mi²	4160 ac
7 mi²	4480 ac
7.5 mi²	4800 ac
8 mi²	5120 ac
8.5 mi²	5440 ac
9 mi²	5760 ac
9.5 mi²	6080 ac
10 mi²	6400 ac
11 mi²	7040 ac
12 mi²	7680 ac
13 mi²	8320 ac
14 mi²	8960 ac
15 mi²	9600 ac
16 mi²	10240 ac
17 mi²	10880 ac
18 mi²	11520 ac
19 mi²	12160 ac
20 mi²	12800 ac
25 mi²	16000 ac
30 mi²	19200 ac
35 mi²	22400 ac
40 mi²	25600 ac
45 mi²	28800 ac
50 mi²	32000 ac
55 mi²	35200 ac
60 mi²	38400 ac
65 mi²	41600 ac
70 mi²	44800 ac
75 mi²	48000 ac
80 mi²	51200 ac
85 mi²	54400 ac
90 mi²	57600 ac
95 mi²	60800 ac
100 mi²	64000 ac
120 mi²	76800 ac
125 mi²	80000 ac
130 mi²	83200 ac
140 mi²	89600 ac
150 mi²	96000 ac
160 mi²	102400 ac
175 mi²	112000 ac
180 mi²	115200 ac
200 mi²	128000 ac
225 mi²	144000 ac
250 mi²	160000 ac
275 mi²	176000 ac
300 mi²	192000 ac
350 mi²	224000 ac
400 mi²	256000 ac
450 mi²	288000 ac
500 mi²	320000 ac
600 mi²	384000 ac
700 mi²	448000 ac
750 mi²	480000 ac
800 mi²	512000 ac
900 mi²	576000 ac
1000 mi²	640000 ac
1200 mi²	768000 ac
1250 mi²	800000 ac
1500 mi²	960000 ac
1750 mi²	1120000 ac
2000 mi²	1280000 ac
2500 mi²	1600000 ac
3000 mi²	1920000 ac
4000 mi²	2560000 ac
4500 mi²	2880000 ac
5000 mi²	3200000 ac
6000 mi²	3840000 ac
7000 mi²	4480000 ac
7500 mi²	4800000 ac
8000 mi²	5120000 ac
9000 mi²	5760000 ac
10000 mi²	6400000 ac
15000 mi²	9600000 ac
20000 mi²	12800000 ac
25000 mi²	16000000 ac
50000 mi²	32000000 ac
75000 mi²	48000000 ac
100000 mi²	64000000 ac

Values based on NIST SP 811 conversion factors

Why Convert Square Miles to Acres?

Converting between square miles (mi²) and acres (ac) is one of the most common area conversions. Whether for engineering, cooking, travel, or science, knowing how to quickly convert mi² to ac saves time and prevents errors.

Area conversions between mi² and ac are critical for real estate valuation, agriculture, and urban planning. Farmers need accurate conversions when calculating crop yields, fertilizer application rates, or irrigation needs across hectares and acres. Homeowners and interior designers use area conversion for flooring, painting, and carpeting estimates to avoid costly material waste or shortages. In environmental science, deforestation rates and habitat protection zones are often reported in differing units depending on the region. A misunderstanding in area units can lead to significant financial discrepancies in property sales or incorrect resource allocation in land management projects.

How to Convert Square Miles to Acres

To convert square miles to acres, use the following formula:

ac = mi² × 640

Example: 1 mi² = 640 ac

For example, 5 mi² = 3200 ac, 10 mi² = 6400 ac, and 100 mi² = 64000 ac. For larger values, 1000 mi² = 640000 ac. Conversely, 1 ac = 0.0015625 mi². Our calculator above performs this conversion instantly with full precision — no rounding errors.

Common Mistakes to Avoid

Squaring the conversion factor: forgetting to square the linear conversion (1 ft = 12 in, but 1 sq ft = 144 sq in).
Confusing land units: mixing up acres and hectares.
Ignoring shape: area formulas differ for circles vs squares.

Pro Tips

Double check squares: Always ensure you're using square units (m²), not linear (m).
Estimation: An acre is roughly a football field (excluding end zones).
Paint calc: 1 gallon of paint covers approx 350-400 sq ft.

What is a Square Mile?

An Imperial/US unit of area equal to 640 acres.

Used for large land areas in the US and UK.

What is a Acre?

The acre is a unit of land area in the Imperial and US customary systems. One acre equals 43,560 square feet or approximately 4,047 square meters.

Acres are standard for measuring large plots of land, agricultural fields, and public parks in the US, UK, and former British Commonwealth countries.

Square Miles → Acres

Square Miles to Acres Formula