Sod Seed Topsoil Calculator

Purpose and model boundary

This calculator estimates what to order for a new lawn that you draw: sod rolls and the pallets they come on, the topsoil to spread under the lawn, and the seed to sow over it. You draw the lawn's outline on a grid and mark up to five areas inside it that are not lawn, such as flower beds, a path, a patio or a tree ring. The spreadsheet measures the net lawn area from the drawing and returns the four quantities for it. It does not price anything, and it does not estimate mulch, edging, fertilizer, irrigation, grading, labour or delivery.

Inputs and units

The drawing is the first input. Its outline is sent as an ordered list of up to 100 corner points and each exclusion as an ordered list of up to 20 points, exactly as on the Area Calculator, which measures the same drawing. The US/Metric switch on the drawing chooses the unit the coordinates are written in, feet for US and metres for Metric, and the unit of every result.

The inputs beside the drawing are:

• Sod roll coverage: the area one roll covers, in square feet (US) or square metres (Metric).
• Sod waste: extra sod for cutting and fitting, as a percentage of the net lawn area. It applies to sod only.
• Rolls per pallet: how many rolls one pallet carries.
• Seed rate: pounds of seed per 1,000 square feet (US) or grams per square metre (Metric).
• Topsoil depth: in inches (US) or centimetres (Metric).

Sod roll coverage, seed rate and topsoil depth have one input for each system, each with its own default: 10 sq ft or 1 m² per roll, 4 lb per 1,000 sq ft or 30 g/m² of seed, and 2 in or 5 cm of topsoil. These are separate market defaults, not conversions of each other: 4 lb per 1,000 sq ft is about 19.5 g/m², not 30, and 10 sq ft is 0.93 m², not 1. Switching between US and Metric shows the other system's inputs with their own values and never converts a number you typed; the value you typed for the system you left is kept for when you switch back, and it is not sent while it is hidden. The spreadsheet reads only the inputs of the selected system. Sod waste (default 5%) and rolls per pallet (default 50) are the same in both systems.

The defaults are typical figures, not values from a code or a standard: a roll's coverage, a pallet's count and a seed rate vary by supplier and by grass. Replace them with the figures on your supplier's quote or the seed label.

Governing relationships

The net lawn area is the area of the outline less the area of each exclusion, each measured by the shoelace formula exactly as on the Area Calculator:

Net lawn area = Gross area − (Exclusion 1 area + … + Exclusion 5 area)

With the net lawn area in square feet (US) or square metres (Metric):

Sod rolls = net lawn area ÷ sod roll coverage × (1 + sod waste), rounded up to a whole roll

Pallets = sod rolls ÷ rolls per pallet, rounded up to a whole pallet

Topsoil (US, cu yd) = net lawn area × topsoil depth in inches ÷ 12 ÷ 27

Topsoil (Metric, m³) = net lawn area × topsoil depth in centimetres ÷ 100

Seed (US, lb) = net lawn area × seed rate ÷ 1,000

Seed (Metric, kg) = net lawn area × seed rate in g/m² ÷ 1,000

The constants are exact: 12 inches in a foot, 27 cubic feet in a cubic yard (a yard is 3 feet), 100 centimetres in a metre, 1,000 square feet in the US seed rate's basis, and 1,000 grams in a kilogram. Waste applies once, to sod, before the rounding up; pallets are counted from the rolls with their waste already included, so nothing is added twice. Topsoil and seed carry no waste.

Calculation sequence

1. The spreadsheet measures the gross area of the outline and the area of each exclusion, and subtracts the exclusions to give the net lawn area.
2. It reads the sod roll coverage, seed rate and topsoil depth of the selected system, and the sod waste and rolls per pallet.
3. Sod rolls: the net lawn area over one roll's coverage, times one plus the waste, is rounded to six decimals and then rounded up to a whole roll. The six-decimal step keeps a figure that is whole on paper whole in the spreadsheet: 1,000 sq ft of 10 sq ft rolls with 10% waste is exactly 110 rolls, and without that step the spreadsheet's arithmetic would give 110.00000000000001 and order 111.
4. Pallets: the sod rolls over rolls per pallet, rounded to six decimals and then up to a whole pallet.
5. Topsoil: the net lawn area times the depth, in cubic yards (US) or cubic metres (Metric), rounded to two decimals as the last step.
6. Seed: the net lawn area times the seed rate, in pounds (US) or kilograms (Metric), rounded to two decimals as the last step.

For the default drawing, a 300 sq ft lawn with the US defaults: 300 ÷ 10 × 1.05 = 31.5, so 32 sod rolls; 32 ÷ 50 rounds up to 1 pallet; 300 × 2 ÷ 12 ÷ 27 = 1.85 cu yd of topsoil; and 300 × 4 ÷ 1,000 = 1.20 lb of seed. In Metric, a 25.44 m² lawn with the Metric defaults gives 27 rolls, 1 pallet, 1.27 m³ of topsoil and 0.76 kg of seed.

Outputs and interpretation

Sod rolls, Topsoil and Seed are the three headline results: the things you buy. Pallets is the number of pallets the sod rolls arrive on. Net lawn area is the area every result is computed from, and Gross area and Exclusion 1 area to Exclusion 5 area show how the drawing arrives at it, 0 for an exclusion slot you did not use. Sod rolls and Pallets are whole numbers; Topsoil is in cubic yards (US) or cubic metres (Metric), Seed in pounds (US) or kilograms (Metric), and the areas in square feet (US) or square metres (Metric), each to two decimals.

The chart shows the sod rolls the spreadsheet computes for the same lawn and roll coverage at every waste allowance from 0% to 20%, in steps of 1%, each rounded up to a whole roll as above, with a dashed line at the rolls needed with no waste allowance, so you can see what each allowance adds. When your sod waste is a whole percentage in that range, its bar is the Sod rolls result. Its points are the spreadsheet's own figures.

A result belongs to the drawing and the inputs it was calculated for. When you change either after pressing Calculate, the result, the chart included, is kept but marked stale until you press Calculate again; changing the value back makes it current again. Switching between US and Metric changes what is sent, so it marks the result stale too.

Validation and status logic

The drawing tool checks every edit to the drawing before it is kept, with the Area Calculator's rules: at least three points per shape, no two consecutive points in the same place, no wall crossing another wall of its shape, every exclusion inside the outline, no two exclusions overlapping, and at most five exclusions. A refused edit leaves the drawing as it was. The drawing tool always writes a shape's points into consecutive rows, with both coordinates of every point; the spreadsheet refuses a request that leaves a blank row between them, or gives a point of the outline or of an exclusion only one coordinate.

The status line is the spreadsheet's own verdict, the first of these that applies:

• NOT VALID: choose US or Metric
• NOT VALID: draw at least three outline points
• NOT VALID: every outline point needs both coordinates
• NOT VALID: every point of exclusion 1 needs both coordinates
• NOT VALID: every point of exclusion 2 needs both coordinates
• NOT VALID: every point of exclusion 3 needs both coordinates
• NOT VALID: every point of exclusion 4 needs both coordinates
• NOT VALID: every point of exclusion 5 needs both coordinates
• NOT VALID: each exclusion needs zero or at least three complete points
• NOT VALID: outline and exclusion points must fill consecutive rows, with no blank row between them
• NOT VALID: the exclusions leave no lawn area, when the net lawn area is zero or less
• NOT VALID: sod roll coverage must be greater than zero
• NOT VALID: enter a sod waste between 0% and 100%
• NOT VALID: enter a topsoil depth of zero or more
• NOT VALID: enter a seed rate of zero or more
• NOT VALID: rolls per pallet must be a whole number of at least one
• CHECK: topsoil depth is zero, so no topsoil is estimated
• OK

The checks on sod roll coverage, seed rate and topsoil depth read the selected system's input only. A NOT VALID: verdict is shown in place of the figures and the chart.

Assumptions and limitations

• The lawn is measured as a flat plan area. A slope or a mound is measured as its footprint, so it needs more sod, soil and seed than the figures say.
• Walls are straight lines between points; a curved edge is drawn as short straight segments, which cut slightly inside the curve.
• The spreadsheet trusts the drawing tool to keep exclusions inside the outline and apart from each other and does not check either itself, so this calculator is offered on its web page only, where the drawing tool enforces them.
• The sod waste applies to the whole lawn; it does not vary with the shape of the edges or the number of exclusions.
• Topsoil is the volume of the layer as spread. It does not allow for settling or compaction.
• The seed estimate is for the net lawn area at one rate. Overseeding, bare-patch repair and a second sowing are not included.
• Drawing needs a mouse, a pen or a touch screen; a drawing prepared elsewhere can be loaded with Import.

Restrictions and non-computing states

This calculator accepts sod roll coverage greater than zero, a sod waste from 0% to 100%, a topsoil depth and a seed rate of zero or more, and a whole number of rolls per pallet of at least one. An input of the system that is not selected is not read. The drawing tool refuses any edit that would leave a shape outside its limits. Nothing is sent until you press Calculate, and pressing it again on an unchanged drawing with unchanged inputs sends nothing.

Errors and warnings

A blank required input keeps Calculate from sending, and pressing it names the input and moves to it. If the calculation service refuses an input, the status line names it and the input is marked until you change it. If the service does not answer, the page says so, keeps your drawing, your inputs and the last result, and lets you press Calculate again. A CHECK: status means the figures are returned with a reason to look again; a NOT VALID: status means they cannot be computed and none are shown.

Sources and further reading

• National Institute of Standards and Technology, Guide for the Use of the International System of Units (SI), NIST Special Publication 811, Appendix B.8. nist.gov. The exact inch (2.54 cm) and foot (0.3048 m) behind the drawing's two systems, from which 12 inches make a foot, and the cubic yard (0.7645549 m³), which is 27 cubic feet.
• Bureau International des Poids et Mesures, The International System of Units (SI), 9th edition (2019). bipm.org. The SI prefixes behind the metric constants: a centimetre is a hundredth of a metre and a kilogram is 1,000 grams.
• Bart Braden, "The Surveyor's Area Formula," The College Mathematics Journal 17, no. 4 (1986): 326-337. doi:10.1080/07468342.1986.11972974. The area of a polygon from the coordinates of its corners, which the spreadsheet uses to measure the lawn from the drawing, as on the Area Calculator.

The default sod roll coverage, rolls per pallet, seed rates and topsoil depths are typical figures chosen for this calculator, not values from these sources or from any code or standard; each system has its own. These sources describe the units and the measurement; they do not certify a particular lawn or its result. Use your supplier's roll size and pallet count and the rate on the seed label, measure the ground you are drawing, and check the figures before ordering.