Soil and lawn establishment
Lawn soil calculator
Calculate sand, soil and amendments from your lawn area and soil depth. Separate materials to bring in, retain and remove, with conversions to tonnes, litres and bags.
Published by InteliDomeUpdated
In this article
Enter the area, depth, preparation method and amendment proportions. The lawn soil calculator works out volumes and separates what to bring in, retain and remove. Conversions to kilograms and tonnes depend on the bulk density of the delivered material; the calculation does not predict how much the mixture will settle.
What to enter in the lawn soil calculator
First decide what needs to change in your soil. The default presets help you compare options; they are not a universal recommendation for every garden. The ranges and conditions for each proportion are explained in How to mix soil for a lawn: ratios for clay, loam and sand.
For your own calculation, enter the area in m², the profile depth in cm and the preparation method. Set both the proportion and the incorporation depth for each amendment. The results further down this article show one specific example without an allowance; the calculator adjusts them to your inputs.
Measure only the area where you will actually prepare the soil. Subtract paths, the patio and flowerbeds. If your garden has distinctly different areas, calculate them separately: the same recipe may not suit both a damp clay corner and a slope that dries out quickly. Then add up the orders for each material.
Profile depth means the thickness of soil used in the calculation. The default 30 cm is a model, not an instruction to excavate the whole garden to that depth. For Actino (formerly Biovin), zeolite and biochar, enter a separate depth measured from the surface: for example, 10 cm means incorporating the amendment throughout the 0–10 cm layer. No amendment should extend below the selected profile.
The soil-type preset sets the starting ratios. Once you adjust the proportions, you are working with your own recipe. Check the depths as well as the percentages: the same proportion in a layer twice as deep requires twice as much amendment for the same area. After changing the inputs, review the full result again.
Soil profile
Base mixture – how much to bring in
Inputs
Remove some soil first. Sand and amendments then replace its volume to retain the specified ground level.
Default example: 100 m² and 30 cm. Adjust it to suit your garden.
Size of the area being prepared.
The example in the article uses 30 cm.
Clay soil reworked with sand: zeolite 2–5%, biochar 2–5%, Actino 2.5–5% of the volume of its own zone.
Presets use the lower end of the amendment ranges. Changing the ratio or amendments switches to a custom recipe.
Amendments take up their volume first. The remainder is the mineral base, divided using this ratio.
How the profile changes
The same inputs — 100 m² and 30 cm — with three preparation methods. Switch between them to see what is removed, what is brought in and how the ground level changes. All three use the same scale, so they can be compared; this controls the same setting as “What I am doing” in the inputs.
Cross-section symbols: turf, existing soil, mixed soil (remaining soil + sand + biochar + Actino + zeolite), to remove, subsoil.
Remove the upper part of the existing soil (hatched area) and replace its volume with the materials brought in. The surface stays at its original level. Mix sand with the remaining soil through the full depth, amendments only within their own zones: biochar and Actino to a depth of 10 cm; zeolite to a depth of 15 cm.
Remove 19.76 m³ of soil; the ground level stays the same.
Keep level, incorporate or create a new layer?
Choose “Keep level” if the surface needs to stay at the same height. In the model, you first remove some soil and replace its volume with sand and amendments. The result separates retained soil, incoming materials and soil to remove. It assumes that the retained soil is suitable for the mixture.
“Incorporate” keeps the existing soil throughout the entered depth and adds materials to it. Here, the entered depth describes the original soil; the resulting profile will be higher. Amendment depths are measured from the new surface.
A higher target sand proportion can mean a surprisingly large delivery and increase in height; check the levels against the patio, paths and water drainage. You cannot keep all the soil, bring in a large volume and expect the surface to stay at the same height.
“New layer” plans the entire volume of the proposed layer from supplied ingredients, including soil. Use it when you are actually ordering a new mixture. Selecting this mode does not confirm that the subsoil is suitable, nor does it address compaction or drainage. It does not automatically include any removal of existing ground beneath the new layer.
How soil and amendment volumes are calculated
The basic relationship is volume = area × depth in metres. For 100 m² and 30 cm, this gives 100 × 0.30 = 30 m³. One cubic metre is 1,000 litres. A useful rule of thumb: a layer 1 cm deep over 1 m² has a volume of 10 litres.
The amendment proportion applies to the volume from the surface down to its own incorporation depth. For example, 2% zeolite to 15 cm over 100 m²: 100 × 0.15 × 0.02 = 0.30 m³, or 300 litres. It is not calculated from the full 30 m³ profile. Actino and biochar are also calculated using their own entered depths.
Layer volumes over an area of 100 m²
| Layer depth | Geometric volume | In litres |
|---|---|---|
| 5 cm | Geometric volume5 m³ | In litres5,000 l |
| 10 cm | Geometric volume10 m³ | In litres10,000 l |
| 20 cm | Geometric volume20 m³ | In litres20,000 l |
| 30 cm | Geometric volume30 m³ | In litres30,000 l |
We calculate 100 m² × depth in metres. This is the volume of the layer, not automatically the amount of new soil to buy. Retained soil, amendment proportions, the calculation mode and actual settling determine the final order. Choose the depth according to the subsoil and the purpose of the work.
Amendments occupy part of the planned volume. Only the remaining mineral base is divided between sand and soil. A 65/35 ratio therefore means 65% sand and 35% soil in this remainder, not another 65% sand on top of the whole mixture. All three amendments may be present together near the surface, while only some extend deeper.
Why 30 m³ of ingredients may not produce 30 m³ of settled mixture
Volume proportions are measured before mixing. Finer particles can fit between coarser ones, and the pore space changes during placement. Adding up the inputs therefore does not guarantee the same volume after settling.
The calculation provides a basis for planning deliveries. Check the actual level as you work; choose an allowance based on the materials and placement method. Keep it separate in the order so it does not change the intended ingredient ratio.
Example: materials for a 100 m² clay-soil garden
Consider a substantial reconstruction where, after assessing the soil, you have chosen a sandier mixture. Set 100 m², a 30 cm profile, “Keep level” and zero allowance. Divide the mineral base 65/35 between sand and existing soil. Actino makes up 2.5% to 10 cm, zeolite 2% to 15 cm and pre-charged biochar 2% to 10 cm. This matches the default clay-soil preset.
The amendments occupy 0.25 + 0.30 + 0.20 = 0.75 m³. Of the original 30 m³, 29.25 m³ remains as mineral base. Its 65% sand share is 19.0125 m³, and its 35% retained-soil share is 10.2375 m³. The overview figures are rounded; use unrounded values to check the total.
You are therefore not ordering the whole 30 m³. Approximately 10.24 m³ of suitable existing soil stays in place, and incoming materials make up the rest. The removal volume describes soil in the original profile; once loosened, it may occupy a different volume on a truck. Clay soil alone does not mean that this extensive reconstruction is necessary.
One mixture, three tasks: bring in, retain, remove
| Material and use | Net volume | Quantity for planning |
|---|---|---|
| Sand — bring in | Net volume19.0125 m³ | Quantity for planning≈ 28.52 t |
| Actino — bring in | Net volume0.25 m³ = 250 l | Quantity for planning150 kg |
| Zeolite — bring in | Net volume0.30 m³ = 300 l | Quantity for planning240 kg |
| Biochar — bring in | Net volume0.20 m³ | Quantity for planning200 l |
| Existing soil — retain | Net volume≈ 10.24 m³ | Quantity for planningDo not buy |
| Existing soil — remove | Net volume≈ 19.76 m³ in the original profile | Quantity for planningCheck volume after excavation |
Model without an allowance. Bulk densities used: sand 1.5 t/m³, Actino 0.6 kg/l and zeolite 0.8 kg/l. Confirm the weights with your supplier. Removed soil is not an additional ingredient in the finished mixture.
Heavier loamy soil: a smaller sand proportion
For a garden with heavier loamy soil and well-maintained topsoil, the model uses a 30/70 sand-to-soil ratio in the mineral base. The default option adds no Actino; adjust the other proportions to the needs of the soil.
If water enters the soil readily and roots grow through it, the preset does not mean you need to reconstruct it. Before using this model, check whether it suits your garden. For help identifying your soil, see How to assess lawn soil: three tests before sowing.
Sandy soil: no additional sand
For a poor, fast-drying sandy garden, the model adds no more sand. The focus is on retaining water and nutrients with suitable amendments. Simply increasing their percentages is not enough: account for existing organic matter, the preparation depth and the particular material.
A higher dose is not automatically better, and two sandy gardens may not need the same mixture. For guidance on identifying sandy soil and what to look for, see How to assess lawn soil: three tests before sowing.
From cubic metres to tonnes, litres and bags
Volume determines the mixture ratio; the unit of sale determines the order. Conversion to weight uses bulk density: the weight of loosely poured material, including the spaces between particles. Weight = volume × bulk density. In our example, 19.0125 m³ of sand at 1.5 t/m³ is approximately 28.52 t.
Sand is usually planned in tonnes, Actino and zeolite in kilograms, and biochar in litres. Check the pack size of the actual product. For example, if your chosen zeolite comes in 20 kg bags, the required 240 kg means 12 bags. Round a partial number of packs up; any surplus is not an instruction to automatically increase the dose in the mixture.
Moisture, particle size and product composition can change the conversion. For biochar, the model value of 0.2 kg/l is only a calculation assumption; the same 200 litres of a moistened or enriched product may weigh differently.
Also check whether you are buying pure biochar or a blend with compost. Compost and other solid carriers have their own volume, which must be included separately in the recipe. The calculator cannot identify the composition of such a product by itself.
The allowance increases only the incoming quantity. It does not change the net mixture ratio, retained soil or removal volume. The calculator uses order = net quantity ÷ (1 − allowance/100). At 10%, a net requirement of 200 litres therefore means ordering approximately 222 litres. This is not simply adding 10%; it covers an assumed loss from the delivered quantity.
Enter prices in the units shown beside each field, using an actual quotation. The estimated material total is not a budget for the entire project: add transport, unloading, soil removal and disposal, and labour separately.
Choose any mycorrhizal product and starter fertiliser according to the product instructions and your recipe. When fertilising, also account for nutrients supplied by Actino and compost; do not automatically combine full doses of these inputs.
After planning deliveries, continue with How to prepare the soil and place the mixture. It covers mixing and checking settlement. For sowing and the first watering, see How to sow a lawn. The following weeks are covered in Caring for a new lawn: from germination to the first cut.
Frequently asked questions about the lawn soil calculation
Before ordering, check the mode, units and actual materials.
Do I need to buy the soil shown in the result?
Only in “New layer” mode. The other modes use suitable existing soil; the result separates incoming materials from soil to remove.
Does lawn soil have to be exactly 30 cm deep?
No. This is a model; enter a depth based on the actual soil and subsoil.
Why might the calculated kilograms differ from the delivery?
Because of bulk density, moisture and material composition. Check these figures with your supplier before ordering and adjust them in the calculator.
Should I always add ten percent for settling?
No. Choose an allowance based on the material and work; the calculator does not predict actual settlement. The allowance does not change the net recipe.
Key takeaways
Now you have a foundation to build on.
- Calculate quantities from area, depth and the selected proportions.
- Separate materials to bring in, soil to retain and soil to remove.
- Conversion to tonnes depends on bulk density; check settlement as you work.
In the next article
The quantities are worked out. What comes first?
Even the right recipe will not help if roots meet a hard barrier beneath the mixture. Work through subsoil preparation, the mixing order and the signs that the surface is ready for sowing.
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