Measuring your space
How to Measure Landscape Beds
Accurate orders start with accurate measurements. Split any bed into simple shapes, measure each one, and add them up.
By Kumar Baniya, MEng in Structural Engineering (University of Leeds) · Last reviewed
What you need
- A long tape measure (a 50 ft or 100 ft tape saves joining shorter measurements).
- A ruler or folding rule for depths.
- Stakes or markers and string for straight baselines.
- Paper to sketch the bed and write each measurement next to the part it belongs to.
Measure in feet and inches, or meters and centimeters — the calculators accept either, and each field has its own unit.
Rectangles and squares
Measure the length and width at right angles to each other. If opposite sides differ a little, measure both and use the average. Area = length × width.
Circles and tree rings
Measure the diameter straight through the center, or measure the distance around the edge (circumference) and divide it by π (about 3.1416). Area = π × (diameter ÷ 2)².
A tree ring is a circle with a hole in the middle. Measure the outer diameter of the mulched ring and the inner diameter you will leave bare around the trunk. The mulch calculator’s tree-ring shape subtracts the inner circle for you. For trees and shrubs, the University of Maryland Extension advises keeping mulch about 3 inches away from the base of the trunk.
Triangles and corners
Measure one side as the base, then the perpendicular height from that base to the opposite corner — at a right angle to the base, not along a sloping edge. Area = ½ × base × height.
Irregular and curved beds
Two methods work well:
Split into shapes
Divide the bed into rectangles, triangles and circle portions that roughly match it. Measure each part, calculate each area and add them. Small gaps and overlaps tend to balance out.
Baseline and offsets
Stretch a string along the length of the bed as a baseline. Every few feet, measure straight out from the string to the bed edge. The area is approximately the interval × (half the first offset + all the middle offsets + half the last offset).
Example: a 20 ft baseline with offsets every 4 ft of 0, 3, 4.5, 5, 4, 0 ft gives 4 × (0/2 + 3 + 4.5 + 5 + 4 + 0/2) = 66 sq ft. Enter it with Area + depth in the calculator. Closer offsets follow curves more accurately.
Leave out anything that will not get material: paths, stepping stones, large rocks or a patio corner. Measure them the same way and subtract.
Measuring depth
Depth is the thickness of material you are adding. For a new bed, it is the depth you plan to spread. For a top-up, push a ruler down to the soil in several places to see how much is left, then use target − existing — the mulch and topsoil calculators have a mode that does this subtraction and returns zero if nothing is needed.
If the depth varies, split the bed into sections with their own depths rather than guessing an average. Each area in the calculators has its own depth.
Worked example
An L-shaped border and a tree ring, all with 3 in of new mulch:
| Part | Area | Volume |
|---|---|---|
| Long leg: 16 ft × 4 ft | 64.00 sq ft | 16.00 ft³ |
| Short leg: 6 ft × 4 ft | 24.00 sq ft | 6.00 ft³ |
| Tree ring: 6 ft outer, 1 ft inner | 27.49 sq ft | 6.87 ft³ |
| Total | 115.49 sq ft | 28.87 ft³ = 1.07 yd³ |
In 2 ft³ bags that is 14.44 bags, so 15 bags. Rounding the total once, instead of rounding each part, avoids buying extra part-bags. The subtotals above are calculated by the same code as the calculators, so they reconcile exactly.
Common mistakes
- Entering depth in feet when you meant inches (3 ft instead of 3 in is twelve times too much).
- Measuring a sloping edge of a triangle instead of its perpendicular height.
- Using a radius where the calculator asks for a diameter.
- Forgetting to subtract paths, trunks or other areas that will not get material.
- Mixing different materials in one total — estimate each product separately.