Garden Bed Area Calculator
Calculate the area and perimeter of rectangular, circular, triangular, or L-shaped garden beds.
Did this tool work for you?
How to use this calculator
Choose your garden bed shape and enter the relevant dimensions. Area determines material quantities; perimeter determines edging length.
- 1
Select your garden bed shape.
- 2
Enter the relevant dimensions in metres.
- 3
Read off the area in m² and sq ft for calculating soil and mulch needs.
- 4
Use the perimeter to purchase the correct amount of garden edging.
Frequently asked questions
Which shapes can the garden bed calculator handle?
Rectangle, circle, triangle and L-shape. Each shape reads its own set of dimension fields, and the fields for other shapes are ignored.
What does the “length” field mean for a circle?
For a circle, the length field is the diameter, not the radius. The tool halves it internally, then computes the area as π × r² and the edging length as π × diameter.
How is a triangular bed’s perimeter calculated?
The tool computes area as half the base times the height. For the perimeter it assumes a right-angled triangle, so the third side is √(base² + height²). If your triangle is not right-angled, the area is still correct but the edging length is only an estimate.
How does the L-shape work?
The L is treated as two rectangles of the same width, one of the long length and one of the short length, with the short section added on top of one end of the long one. Area is (long + short) × width, and the perimeter is 2 × (long + short + width), which matches the outline of the combined shape.
Does the edging figure include any extra length?
No. Edging needed equals the perimeter exactly. Overlaps at joints, corner pieces and offcuts are not added, so allow a margin yourself.
Which units does it use?
Dimensions are in metres. Area is shown in square metres and in square feet, using a factor of 10.7639, and the perimeter is shown in metres.
Can it handle freeform or kidney-shaped beds?
No. Split the bed mentally into rectangles, circles or triangles, run each one, and add the areas together. The tool does not sum several shapes itself.
Measuring garden bed area and edging length
Why area and perimeter go together
Area decides how much soil, mulch, seed or fertiliser a bed takes, while perimeter decides how much edging, fencing or liner you buy. This calculator returns both from the same dimensions so you do not need two separate lookups. It supports four footprints: rectangle, circle, triangle and an L made of two rectangles. Dimensions are entered in metres, and the results come back in square metres, square feet and linear metres, so the same numbers work whether your suppliers quote metric or imperial.
Formulas for each shape
The table gives the area and perimeter formulas used in the code and the dimensions each shape needs.
| Shape | Inputs read | Area | Perimeter |
|---|---|---|---|
| Rectangle | Length, width | L × W | 2 × (L + W) |
| Circle | Diameter (the length field) | π × (d ÷ 2)² | π × d |
| Triangle | Base, height | ½ × base × height | base + height + √(base² + height²) |
| L-shape | Long section, short section, width | (long + short) × width | 2 × (long + short + width) |
Worked results for seven beds
Here are results the calculator returned for seven fixed beds, with both metric and square-foot areas.
| Bed | Area (m²) | Area (sq ft) | Perimeter (m) |
|---|---|---|---|
| Rectangle 3 m × 1.5 m | 4.50 | 48.4 | 9.00 |
| Rectangle 6 m × 1.2 m | 7.20 | 77.5 | 14.40 |
| Circle, 3 m diameter | 7.07 | 76.1 | 9.42 |
| Circle, 2 m diameter | 3.14 | 33.8 | 6.28 |
| Triangle, base 2 m, height 1.5 m | 1.50 | 16.1 | 6.00 |
| L-shape, 4 m + 2 m, 1 m wide | 6.00 | 64.6 | 14.00 |
| L-shape, 5 m + 3 m, 1.2 m wide | 9.60 | 103.3 | 18.40 |
Reading the L-shape and triangle
The 4 m and 2 m L-shape stands on a footprint that is 4 m across and 3 m deep, so its outline measures 14 m, the same as that bounding rectangle. The 3 m circle covers 7.07 m² against 4.50 m² for the 3 m by 1.5 m rectangle, yet its edging is 9.42 m against 9.00 m, because a round outline encloses more area per metre of border. For the triangle, the 6.00 m perimeter works only because the sides are 2, 1.5 and 2.5, a right-angled set. A scalene triangle with the same base and height would need different edging.
Using the figures downstream
Take the area into a mulch, seed or soil calculator and the perimeter into your edging order, adding your own allowance for joints and cuts. For a bed that combines several shapes, run each section on its own and add the areas. Measure along the surface at ground level, and remember the tool assumes a flat bed. A bed on a slope has more surface than its plan view, but the calculator reports plan area only. If an edging product is sold in fixed lengths, divide the perimeter by that length and round up to find the number of pieces.
Learn more from an authoritative source:
WikipediaWallpaper Roll Calculator
Calculate how many wallpaper rolls you need for a room, accounting for doors, windows, and pattern repeats.
Fence Stain Calculator
Calculate how much fence stain or paint you need based on fence size, style, and number of coats.
Mulch Calculator
Calculate how many cubic yards or cubic metres of mulch you need for a garden bed, plus bags required.
Raised Bed Soil Calculator
Calculate how much soil and compost you need to fill a raised garden bed, with mix breakdowns.
Lawn Seed Calculator
Calculate exactly how much grass seed you need based on lawn area, grass type, and seeding purpose.
Plant Spacing Calculator
Calculate how many plants fit in a garden bed using square grid or triangular offset planting patterns.
Results are estimates for informational purposes only and do not constitute professional financial, medical, legal, or technical advice. Read full disclaimer →