How many acres is a quarter section of land?

A quarter section is 160 acres. A full section is 1 square mile = 640 acres. A quarter section is 2,640 ft × 2,640 ft. A half section is 320 acres. Township sections follow the PLSS (Public Land Survey System) used throughout the western United States.

How many acres does a center pivot irrigate on a quarter section?

A standard center pivot inscribed in a quarter-section square (2,640 ft × 2,640 ft) has a radius of 1,320 ft and irrigates about 125.7 acres — 78.5% of the 160-acre field. The 4 dry corners total about 34.3 acres (8.6 acres each). An end gun can add several acres of irrigation beyond the square boundary.

How do I calculate acres from feet?

1 acre = 43,560 square feet. For a rectangle: multiply length (ft) × width (ft) then divide by 43,560. Example: 1,320 ft × 1,320 ft = 1,742,400 sq ft ÷ 43,560 = 40 acres. For a circle: π × radius² ÷ 43,560. This calculator handles all conversions automatically.

What are the dry corners of a pivot-irrigated field?

Dry corners are the 4 triangular-ish areas at the corners of a square field that a standard center pivot cannot reach. For a quarter section, each dry corner is about 8.6 acres (34.3 acres total). Farmers typically dryland crop dry corners, leave them fallow, or install corner-arm systems (swing arms) to irrigate them.

What is an end gun on a center pivot?

An end gun is a large impact sprinkler mounted at the outer end of a center pivot that fires during specific portions of the pivot rotation — typically when the pivot is pointed toward the middle of each side of the square field. It extends the wetted area beyond the pivot's normal radius, irrigating arc-shaped segments outside the pivot circle boundary.

How do I calculate the outer ring area of a pivot field?

Outer ring (annulus) area = π × (R² − r²), where R is the full pivot radius and r is the inner edge of the ring. Example: 1,320 ft pivot, outer 200 ft ring: π × (1,320² − 1,120²) = π × (1,742,400 − 1,254,400) = 1,532,902 sq ft = 35.2 acres. This helps estimate the acreage covered by the last passes before the pivot completes a revolution.

How many acres in a chain?

1 chain = 66 feet. 1 acre = 10 square chains (1 chain × 10 chains = 1 acre). A 40-acre field is 20 chains × 20 chains. Chains are the traditional US survey unit — a quarter section is 40 chains × 40 chains = 1,600 square chains = 160 acres.

How do I convert rods to acres?

1 rod = 16.5 feet = 0.25 chains. 1 acre = 160 square rods. A 40-acre field is 80 rods × 80 rods. Rods are commonly used in older US land records and survey descriptions, particularly in Midwest and Pacific Northwest deed descriptions.

What is a pivot field corner arm?

A corner arm (also called swing arm or corner system) is a retractable extension attached to the last tower of a center pivot that swings outward to irrigate the dry corners of a square field. Corner arms can cover an additional 10–20 acres per corner depending on arm length and field size, potentially increasing a quarter section's irrigated area from 126 to 150+ acres.

How do I calculate the area of an irregular field?

For an irregular field, divide it into known shapes (rectangles, triangles, trapezoids) that together cover the field, calculate each section separately, then add the areas. GPS-based field mapping tools can measure irregular boundaries precisely. For farm planning, the calculator's trapezoid mode handles many irregular field shapes that have two parallel sides of different lengths.

How do I calculate hectares from acres?

1 acre = 0.404686 hectares. 1 hectare = 2.47105 acres. Multiply acres by 0.404686 to get hectares, or multiply hectares by 2.47105 to get acres. A standard quarter section of 160 acres = 64.75 hectares. A 100-acre field = 40.47 hectares.

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Field Size Calculator

Rectangle · Circle · Triangle · Trapezoid · Pivot Field with dry corners & end gun

Field Shape

Input Units

Known Field Size (acres — optional)

Enter known acreage to auto-fill the radius or side length below.

Radius (ft)

1,320 ft radius = standard quarter-section pivot = 125.7 acres.

Pivot Circle (optional)

Pivot Radius (ft)

If a center pivot irrigates this field, enter its radius. Leave blank for dryland. Auto-calculates as half the field's shortest dimension if left blank after providing field size.

End Gun Extension (ft)

Extra reach beyond pivot radius. Typical: 100–200 ft.

Outer Buffer (optional)

Buffer Width (ft)

Width of the buffer strip around the field perimeter. For dryland: buffer of the full field area. For irrigated fields with a pivot: buffer of the pivot circle only (annulus).

Select a shape and enter dimensions

Enter field dimensions and press Calculate.

Disclaimer — Field size calculations are estimates based on geometric formulas and your inputs. Actual field boundaries and legal descriptions should be verified with official surveys, FSA records, or GPS mapping. For legal or title purposes, consult a licensed land surveyor.

Frequently Asked Questions

A quarter section is 160 acres. A full section is 1 square mile = 640 acres, so a quarter section is 2,640 ft × 2,640 ft. Half sections are 320 acres. The PLSS (Public Land Survey System) divides townships into 36 sections, each 1 mile square.

A standard center pivot on a 2,640 ft × 2,640 ft quarter section has a 1,320 ft radius and irrigates about 125.7 acres — 78.5% of the 160-acre field. The 4 dry unirrigated corners total about 34.3 acres (8.6 acres each). An end gun firing on 4 sides can add several additional acres of irrigation outside the square boundary.

1 acre = 43,560 square feet. For a rectangle: multiply length × width in feet, then divide by 43,560. For a circle: π × radius² ÷ 43,560. Example: a 1,320 ft × 1,320 ft square = 1,742,400 sq ft ÷ 43,560 = 40.0 acres.

Dry corners are the 4 areas at the corners of a square field that a standard center pivot cannot reach. For a quarter section, each corner is about 8.6 acres (34.3 acres total). Farmers typically dryland crop these corners, leave them fallow, or install corner-arm systems to irrigate them.

An end gun is a large impact sprinkler at the outer end of a center pivot that fires during specific arcs — typically when the pivot faces the middle of each side of the square field. It irrigates arc-shaped areas outside the pivot circle, adding several acres to total irrigated area depending on extension distance.

Outer ring area = π × (R² − r²), where R is the full pivot radius and r is the inner edge of the ring. Example: 1,320 ft pivot, 200 ft wide ring: π × (1,320² − 1,120²) = 1,532,902 sq ft = 35.2 acres. The ring acreage helps estimate the yield impact of the last passes before the pivot completes a full rotation.

1 chain = 66 feet. 1 acre = 10 square chains. A 40-acre field is 20 chains × 20 chains. A quarter section is 40 chains × 40 chains = 160 acres. Chains are the traditional US survey unit used throughout PLSS land records.

1 rod = 16.5 feet. 1 acre = 160 square rods. A 40-acre field is 80 rods × 80 rods. Rods appear frequently in older US deed descriptions, particularly in Midwest and Pacific Northwest land records.

A 1,320 ft radius circle has area = π × 1,320² = 5,474,886 sq ft ÷ 43,560 = 125.66 acres. This is the standard quarter-section pivot circle. A 660 ft radius circle (eighth section) = 31.4 acres. A 1,500 ft radius = 162.7 acres.

1 acre = 0.404686 hectares. 1 hectare = 2.47105 acres. A 160-acre quarter section = 64.75 hectares. A 100-acre field = 40.47 hectares. Multiply acres × 0.404686 to get hectares.

Divide the irregular field into known shapes — rectangles, triangles, and trapezoids — calculate each section separately, then add the results. The trapezoid mode handles many fields with two parallel sides of different lengths. GPS-based farm management software can measure irregular boundaries precisely from satellite or drone imagery.

A corner arm (swing arm) is a retractable extension on the last tower of a center pivot that swings outward to irrigate dry corners. Corner arms can add 10–20 acres per corner, potentially increasing a quarter section from 126 to 150+ irrigated acres. This calculator's end-gun mode estimates the arc-shaped area outside the normal pivot circle.