Garden Bed Area Calculator for Any Shape
Pick the shape of your bed, enter the measurements it asks for, and get the area, the perimeter and the edging length with a small allowance for cuts and overlaps. Fill in only the fields for your shape; the others are ignored. After switching units, re-enter your measurements.
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Formula
- Rectangle:
area = length x width,perimeter = 2 x (length + width) - Circle:
area = pi x (diameter / 2)^2,perimeter = pi x diameter - Triangle (three sides a, b, c):
s = (a + b + c) / 2,area = sqrt(s (s - a) (s - b) (s - c))(Heron),perimeter = a + b + c - Trapezoid (isosceles):
area = (top + bottom) / 2 x height,leg = sqrt(height^2 + ((bottom - top) / 2)^2),perimeter = top + bottom + 2 x leg - L-shape:
area = length x width - cut length x cut width,perimeter = 2 x (length + width) edging = perimeter x (1 + extra %). 1 m2 = 10.7639 ft2.
Worked example
| Shape | Measurements | Area | Perimeter |
|---|---|---|---|
| Rectangle | 10 x 4 | 40 | 28 |
| Circle | diameter 6 | 28.27 | 18.85 |
| Triangle | 3, 4, 5 | 6 | 12 |
| Trapezoid | 4, 8, height 3 | 18 | 19.21 |
| L-shape | 10 x 8, cut 4 x 3 | 68 | 36 |
For the 10 x 4 rectangle with 5% extra, edging is 28 x 1.05 = 29.4.
Assumptions
- Measurements are in feet or metres, and areas in square feet or square metres.
- The trapezoid has two equal slanted sides, and the L-shape's cut-out is a rectangle at a corner.
Frequently asked questions
How do I find the area of a circular garden bed?
Use pi x radius squared. For a bed 6 feet across the radius is 3 feet, so the area is 3.1416 x 9 = 28.27 square feet, and the edge is pi x 6 = 18.85 feet long.
How do I measure an L-shaped bed?
Measure the outer rectangle, then the rectangle cut out of one corner, and subtract. A 10 by 8 foot outline with a 4 by 3 foot corner removed has 80 - 12 = 68 square feet. The perimeter equals the outer rectangle's, 2 x (10 + 8) = 36 feet.
How much edging should I buy?
Edging equals the perimeter plus an allowance for cuts, curves and overlaps. A 10 by 4 foot bed has a 28 foot perimeter, and 5 percent extra gives 29.4 feet. Leave out any side that meets a wall or path.
How is a trapezoid bed calculated here?
The area is the average of the two parallel sides times the height between them. Sides of 4 and 8 feet with a height of 3 feet give 6 x 3 = 18 square feet. The calculator assumes both slanted sides are equal, so each is about 3.61 feet and the perimeter is 19.21 feet.
How many square feet is an 8x4 garden bed?
Multiply the length by the width: 8 x 4 = 32 square feet. The perimeter is 24 feet, so with the default 5 percent allowance you would buy 25.2 feet of edging.
How do I calculate the area of a 10 foot round flower bed?
Use pi x radius squared. A 10 foot diameter gives a 5 foot radius, so the area is 3.1416 x 25 = 78.54 square feet and the edge is 31.42 feet long, or 32.99 feet of edging with 5 percent extra.
How many square feet is a 3 m by 12 m bed?
In metric mode 3 x 12 = 36 square metres, which is 387.5 square feet. The perimeter is 30 m, or 31.5 m of edging with 5 percent extra.