Calculate field size in acres or hectares from measured dimensions. Supports rectangular fields, right triangles, trapezoids, and circular pivot fields. For pivot fields, enter the lateral length to get irrigated circle area instantly. Results include area in acres, hectares, and square feet or square metres. Useful for crop insurance documentation, rental agreements, custom farming invoices, and precision agriculture planning.
Rectangle · Circle · Triangle · Trapezoid · Pivot Field with dry corners & end gun
Enter field dimensions and press Calculate.
Field size in agriculture is most commonly measured in acres (US) or hectares (international). One acre equals 43,560 square feet or about 0.405 hectares. One hectare equals 10,000 square meters or about 2.47 acres. Irregular field shapes are measured by GPS, survey, or by breaking the field into simpler geometric shapes (rectangles, triangles, circles) and summing their areas. Center pivot irrigation systems create circular fields — the area of a full circle is π × radius², where the radius is the pivot lateral length.
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 Western US 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.