Formula used
Rectangle: area = length × width Square: area = side² Circle: area = π × radius² Oval: area = π × major radius × minor radius Triangle: area = ½ × base × height Trapezoid: area = ((parallel side A + parallel side B) ÷ 2) × height L-shape: area = outer rectangle − cut-out rectangle Soil volume = area × net depth × number of identical areas Adjusted volume = base volume × (1 + total allowance ÷ 100) Bags required = ceiling(adjusted volume ÷ bag volume) Estimated weight = adjusted volume × soil density
How to use the calculator
Choose the project type and add every garden area. Enter measured dimensions using one consistent unit. Add existing depth only for top-up calculations.
Select waste, settling, compaction, and soil density values. Choose a bag size or bulk price. Review the calculated volume before ordering materials.
Set a soil mix or enter custom component percentages. Add prices, delivery, labour, and tax. Export results for purchasing and project records.
Suggested soil depths
| Garden use | Typical depth | Planning note |
|---|---|---|
| Lawn top-dressing | 0.5–1.5 cm | Apply thinly to avoid smothering grass. |
| Annual flowers | 15–25 cm | Loosen the soil beneath compact layers. |
| Vegetable bed | 25–45 cm | Deep-rooted crops benefit from greater depth. |
| Raised garden bed | 30–60 cm | Consider woody filler only when suitable. |
| Herb planter | 20–30 cm | Use excellent drainage for Mediterranean herbs. |
| Shrub planting area | 30–60 cm | Match amendments to local soil conditions. |
Soil density reference
| Material | Approximate density | Use |
|---|---|---|
| Light potting mix | 350–550 kg/m³ | Containers and planters |
| Finished compost | 550–850 kg/m³ | Organic matter improvement |
| Garden soil | 1,000–1,300 kg/m³ | General beds and borders |
| Screened topsoil | 1,200–1,500 kg/m³ | Bulk bed filling |
| Wet compact soil | 1,500–1,800 kg/m³ | Heavy handling estimates |
Worked example
| Input | Example value | Calculation |
|---|---|---|
| Bed size | 4 m × 1.2 m | Area = 4.8 m² |
| Soil depth | 0.30 m | Base volume = 1.44 m³ |
| Total allowance | 15% | Adjusted volume = 1.656 m³ |
| Bag size | 40 litres | 1.656 ÷ 0.04 = 41.4 bags |
| Purchase quantity | 42 bags | Always round complete bags upward |
Calculation history
Recent successful totals are stored in this browser.
Frequently asked questions
How much extra soil should I order?
Five to fifteen percent suits many garden projects. Loose soil often settles after watering. Supplier moisture levels can also change delivered volume.
Should top-up depth subtract existing soil?
Yes, when a final target depth is known. Enter both desired and existing depths. The calculator uses only the missing depth.
Why are soil bags rounded upward?
Retailers usually sell only complete bags. Partial bag estimates cannot be purchased directly. Rounding upward prevents material shortages during installation.
Can I calculate several beds together?
Yes, add each bed as another area. Shapes and depths may differ completely. The calculator combines every valid area automatically.
How accurate are soil weight estimates?
Weight depends strongly on moisture and compaction. Preset densities provide practical planning estimates. Confirm vehicle limits before transporting heavy soil.
What if my garden is irregular?
Divide it into smaller measurable shapes. Calculate each section as another area. Alternatively, enter a surveyed custom surface area.
Do mix percentages need total 100%?
No, the calculator normalises entered positive values. Their proportions remain the same. Exact percentages still make planning easier.
Should I buy bags or bulk soil?
Bags suit smaller projects and limited access. Bulk delivery often suits larger volumes. Compare material, delivery, storage, and handling costs.
Can this calculate planter soil?
Yes, use rectangular or circular shapes. Enter internal dimensions rather than external dimensions. Include several identical planters using the count.
Does the result replace supplier advice?
No, suppliers may use different bag volumes. Natural materials vary by moisture level. Confirm final quantities before placing expensive orders.
Important note
This calculator provides planning estimates, not guaranteed supply quantities. Soil volume changes through settling, moisture, and compaction. Confirm specifications with your landscape supplier before purchase.