Irregular Yard Area Calculator (Four Sides)

This calculator estimates the area of a four-sided yard or lawn whose sides are not quite equal. Enter the two lengths and the two widths, measured along opposite sides; you get the approximate area in square feet, square yards, acres and square metres.

Formula

Area ≈ (average of the two lengths) × (average of the two widths) = (a + b) ÷ 2 × (c + d) ÷ 2. Square yards = ft² ÷ 9; acres = ft² ÷ 43,560; m² = ft² × 0.09290304.

• a, b: the two opposite long sides in feet
• c, d: the two opposite short sides in feet

Worked Example

A yard measured at 50 ft and 46 ft long, 30 ft and 34 ft wide.

1. Average length = (50 + 46) ÷ 2 = 48 ft
2. Average width = (30 + 34) ÷ 2 = 32 ft
3. Area = 48 × 32 = 1,536 ft²
4. That is 170.67 yd², 0.0353 acres or 142.70 m²

How to use the result

Use the area to order sod, seed, fertilizer or mulch. For a yard with more than four sides, split it into four-sided pieces and triangles, find each, and add them.

Limits and common mistakes

• The averaging rule is exact for rectangles and close for shapes near a rectangle. For a strongly skewed shape it overstates the area; then split the yard into triangles (area = base × height ÷ 2) or measure the diagonals.
• Measure along the ground; on steep slopes the real surface is larger than the plan area.
• Leave out beds, patios and buildings you will not cover.

Frequently Asked Questions

How do I measure an odd-shaped lawn?

Split it into rectangles, triangles and circles, find each area and add them.

Is the average-of-sides method accurate?

Within a few percent for near-rectangles; less so for skewed shapes.

How many square feet are in an acre?

43,560 ft².

Can I enter metres?

Enter feet; 1 m = 3.2808 ft.

in a | Length, side 1 | ft | 50 | 0 | 100000
in b | Length, opposite side | ft | 46 | 0 | 100000
in c | Width, side 1 | ft | 30 | 0 | 100000
in d | Width, opposite side | ft | 34 | 0 | 100000
out area | Approximate area | ft² | (a + b) / 2 * (c + d) / 2 | 0
out yd | Approximate area | yd² | area / 9 | 2
out ac | Approximate area | acres | area / 43560 | 4
out m2 | Approximate area | m² | area * 0.09290304 | 2