What this planner works out
You enter the beds, borders or circles you want to cover, the depth you choose, and the bag or bulk sizes you are comparing. The planner adds the areas together, works out the volume, adds your own allowance if you want one, and rounds up to whole bags and whole bulk units. Each option shows what you would buy, what is left over and what it costs, and it names the cheaper of the options you entered.
One page covers mulch, bark, topsoil, compost, decorative gravel, sandbox sand, the fill for raised beds and the potting mix for pots, planters and window boxes. The material type only changes the wording; the arithmetic is the same for all of them.
Four optional sections, all off until you switch them on, add what you buy alongside the fill: landscape fabric and pins, garden edging and stakes, the boards for a raised-bed frame, and stepping stones along a path. They never change the fill volume.
How to measure
- Rectangular beds: measure the length and the width. Split an L-shaped bed into two rectangles and add each as its own area.
- Circles: measure across the widest point through the middle, which is the diameter. A tree ring with a trunk in the middle is close enough as a full circle.
- Odd shapes: if you already know the surface, for example from a plan, use “known area”.
- Raised beds: measure inside the frame. The boards take up space, so outside dimensions overstate the fill. The fill height is how deep you fill the bed, not the height of the boards.
- Pots, planters and window boxes: measure inside, at the height you will fill to, and the fill height from the inside base. Enter the number of identical pots; add another area for pots of another size.
For depth, enter the depth you choose. As a commonly quoted example only, many guides suggest 2–3 in (5–8 cm) of mulch; that is not a recommendation for your bed, and labels for other materials quote other figures.
The method
- Volume per area = surface × depth. A circle’s surface is π × diameter² ÷ 4. Pots are the number of pots × the volume of one pot (see below).
- Add the areas that use the same material, before any rounding.
- Allowance (optional): your own percentage for settling, top-up or spillage. It is 0 unless you change it.
- Packages: divide by the bag or bulk volume and round up, never down: 13.2 bags means 14, because 13 would leave you short (see how pack rounding works). Each option is rounded on its own.
- Leftover = what you buy minus what you need.
Worked example in metric
A border of 12 m² mulched 5 cm deep, with 50 L bags:
- Volume: 12 m² × 0.05 m = 0.6 m³ = 600 L
- Bags: 600 L ÷ 50 L = 12 bags, nothing left over
- With a 10% allowance: 600 × 1.1 = 660 L, and 660 ÷ 50 = 13.2, so 14 bags (700 L), 40 L left over
Worked example in feet
A bed 10 ft × 4 ft at 3 in (0.25 ft), with 2 ft³ bags or bulk sold by the cubic yard:
- Volume: 10 × 4 × 0.25 = 10 ft³, which is 10 ÷ 27 = about 0.37 yd³
- Bags: 10 ÷ 2 = exactly 5 bags
- Bulk: 1 yd³, with 27 − 10 = 17 ft³ left over
A circle 6 ft across at 3 in: π × 6² ÷ 4 = about 28.27 ft², × 0.25 ft = about 7.07 ft³, so 4 bags of 2 ft³.
Bags or bulk?
Bags are easy to carry and store, and you buy only what you need. Bulk is often cheaper per cubic yard or cubic meter on a larger job, but compare the prices you are quoted, delivery included: a delivery may have a minimum and a fee, and the pile needs space. Enter a price for both options and the planner compares the totals. Check the stated volume of a bulk bag: bulk bags vary and some hold less than a cubic meter, so type the figure printed on the bag or quoted by the supplier. How many bags come on a pallet depends on the supplier and the bag size, so ask them if you are arranging a delivery; the planner counts the bags you need.
Raised beds and blends
Two raised beds of 2.4 × 1.2 m inside, filled 0.3 m deep, hold 2 × 0.864 = 1.728 m³. With a 15% top-up allowance that is about 1.99 m³, or 40 bags of 50 L. If you fill with a mix, enter your own ratio, for example 60 and 40, and the planner splits the volume: about 1.19 m³ and 0.79 m³. It does not suggest a mix.
Landscape fabric and pins
Fabric comes in rolls of a fixed width, so a bed is covered by strips laid side by side with an overlap at each seam. The planner lays the strips along each area’s length (swap length and width to lay them the other way):
- Strips = 1 if the width fits in one roll width, otherwise (width − overlap) ÷ (roll width − overlap), rounded up.
- Strip length = length + the tuck at both ends, if you fold the edges in.
- Per roll = how many whole strips fit along one roll. Strips of the same length from different areas share rolls; strips of different lengths never share one. A strip longer than a roll is not joined for you.
- Pins = edge length ÷ spacing, rounded up, plus for every seam (length ÷ spacing, rounded up) + 1.
Worked example: a 4 × 2.5 m bed, 1 m × 10 m rolls and a 10 cm overlap. (2.5 − 0.1) ÷ 0.9 = 2.67, so 3 strips of 4 m; a 10 m roll holds 2 of them, so 2 rolls, with 8 m left over. With pins every 1 m: 13 m of edge gives 13 pins, and the 2 seams take 5 each, so 23 pins, one pack of 50. A circle is covered by strips across its full diameter. The overlap and pin spacing come from the fabric and pin instructions; the figures here are only examples.
Edging and stakes
Edging is bought in strips, pieces or coils of a fixed length. Each edge you line is one run: every area is a closed loop around it, or you type one length as an open run (with two ends) or a closed loop.
- Pieces per run = run × (1 + your allowance) ÷ (piece length − overlap at the joints), rounded up. Each run is rounded on its own, because an offcut from one bed is not carried to the next.
- Stakes = a number per piece, or run ÷ spacing rounded up, plus one at the end of an open run.
Worked examples: 20.6 m of edge with a 5% allowance is 21.63 m, so 22 strips of 1 m. One open run of 55 ft in 40 ft coils is 2 coils; stakes every 3 ft need 55 ÷ 3 = 18.3, rounded up to 19, plus 1 = 20 stakes.
Check for buried cables and pipes before digging or driving stakes (in many places there is a free call-before-you-dig service).
Raised-bed frame boards
For every area with the shape “Raised bed” the planner counts the boards for the sides, using the internal size and the fill height you entered:
- Courses = fill height ÷ board width, rounded up.
- Sides per course: two long and two short. If the long sides run past the ends, the long sides are the internal length + 2 × board thickness and the ends are the internal width; if the ends run past, it is the other way round.
- Boards: sides of one length are cut from whole boards, as many as fit in one board including the saw cut, and rounded up. Different lengths never share a board, and a side longer than one board is not joined for you.
Worked example in feet: a bed 93 × 45 in inside, one course of 2×12 boards (actual size 11.25 × 1.5 in), 8 ft boards, long sides past the ends. The long sides are 93 + 3 = 96 in, one per board, so 2 boards; the ends are 45 in, and two fit in one 96 in board, so 1 board: 3 boards. Outside, that bed is the familiar 4 × 8 ft.
Worked example in metric: a bed 2.324 × 1.124 m inside and 0.30 m deep, 150 × 38 mm boards of 2.4 m. 0.30 ÷ 0.15 = 2 courses; four long sides of 2.4 m take 4 boards, and four ends of 1.124 m fit two to a board, 2 boards: 6 boards.
This is a count of equal pieces, not an optimized cutting plan.
Pots, planters and window boxes
Every row with the shape “Pots or planters” is a number of identical pots, round or square/rectangular, with straight or tapered sides. The planner works out one pot and multiplies by the number of pots:
- Straight round pot: π × diameter² ÷ 4 × fill height.
- Tapered round pot (top diameter D at the fill line, bottom diameter d, fill height h): π × h × (D² + D × d + d²) ÷ 12, the volume of a cone frustum. With d = D it is the straight pot again.
- Straight square or rectangular pot: length × width × fill height.
- Tapered square or rectangular pot (top L × W, bottom l × w): h ÷ 6 × (2 × L × W + 2 × l × w + L × w + l × W). For square pots this is the familiar h ÷ 3 × (top area + bottom area + √(top area × bottom area)); the longer form is also exact for window boxes whose top and bottom have different proportions.
Worked example in metric: ten straight pots 30 cm across, filled 25 cm deep: π × 0.3² ÷ 4 × 0.25 = about 0.01767 m³ (17.67 L) each, 176.7 L in all, so 176.7 ÷ 50 = 3.53, 4 bags of 50 L with 23.3 L left. Three tapered planters, 40 cm across the top, 30 cm at the bottom, filled 35 cm: π × 0.35 × (0.16 + 0.12 + 0.09) ÷ 12 = about 0.0339 m³ (33.9 L) each, 101.7 L in all, 3 bags of 40 L. Both rows together with 50 L bags: 278.4 L, 6 bags, because rows of the same material are added before rounding.
Worked example in feet: twelve pots 12 in across, filled 10 in deep: π × 1² ÷ 4 × 10/12 = about 0.654 ft³ each, about 7.85 ft³ in all, 4 bags of 2 ft³.
A tapered window box 80 × 20 cm at the top and 70 × 15 cm at the bottom, filled 15 cm: 0.15 ÷ 6 × (2 × 0.16 + 2 × 0.105 + 0.12 + 0.14) = 0.01975 m³, about 19.75 L.
The planner does not suggest a potting mix, a drainage layer or how full to fill a pot.
Stepping stones
The stepping-stones section counts stones along one path. You enter the path length, the size of one stone measured along the path, and the gap you want between two stones (0 if they touch); the planner never suggests a stride.
- Rule: the first stone starts at the beginning of the path, the next one starts one stone plus one gap later, and the last stone must end on the path: stones = (path − stone) ÷ (stone + gap), rounded down, + 1.
- Packs (optional): stones ÷ stones per pack, rounded up.
- Path left after the last stone = path − (stones × stone + (stones − 1) × gap).
Worked example: a 6 m path, 45 cm stones and 15 cm gaps (60 cm from the start of one stone to the next): (6 − 0.45) ÷ 0.6 = 9.25, rounded down to 9, + 1 = 10 stones, with 15 cm left after the last one. In feet: a 20 ft path with 18 in stones and 6 in gaps: (20 − 1.5) ÷ 2 = 9.25, so 10 stones. If the path were exactly 5.85 m, the tenth stone would end exactly at the end of the path, still 10; at 5.84 m it no longer fits, so 9.
Why other calculators can say one more or one less: “path ÷ (stone + gap)” leaves room for a gap after the last stone, so it is one short when the last stretch holds a whole stone (5.85 m: 9.75, rounded down to 9); “path ÷ stride
- 1” puts a stone at the very end, so the last stone can lie partly past the path (6 m: 11). The planner states its rule and shows the path left after the last stone so you can check it.
To work out gravel between the stones, enter the path as an area; the planner does not subtract the stones.
Sandbox sand
A sandbox is a box filled to a depth you choose, so it works like any other area: measure inside the box. The Sandbox example button opens editable example values: a 4 × 4 ft box filled 6 in deep is 4 × 4 × 0.5 = 8 ft³, which is 16 bags of 0.5 ft³. These are example numbers, not a product’s values. Play sand is often labeled by weight; use the volume printed on the bag, or enter the density from the seller to see the weight. Choose sand sold for play areas and follow the instructions on the bag.
Why weight needs a density
Bags and bulk are often sold by volume, but gravel and some soils are sold by the tonne, and your trailer or wheelbarrow has a weight limit. Weight is volume × density, and density depends on the material, its moisture and how tightly it is packed. Loose material, as it comes off the truck, weighs less per cubic foot than the same material after it has been compacted or has settled. The planner never assumes a density: enter the figure from your supplier for the material as delivered. For example, at a density of 1,600 kg/m³ (an example figure, not a value for any product), 0.6 m³ weighs 960 kg.
Limits
This is a quantity estimate from your own measurements and package values. It gives no drainage, plant, soil or contamination advice, and it does not design a base for paths, patios or driveways: gravel here means decorative cover. Frame boards and stepping stones are counts only, with no strength, bracing, timber, base or bedding advice. It does not suggest a depth for playground surfacing or a material for use next to a fire.