Calculation methods
The formulas, worked examples, assumptions and limits behind every tool.
Raised bed soil ↗
Volume = length × width × depth × bed count. Add your allowance, then round the bag count up.
Example: 240 × 120 × 30 cm = 864 L. With 10% extra: 950.4 L, or 24 bags of 40 L.
Use internal measurements and the actual depth you want to fill. Existing soil and drainage layers reduce the required depth. This is a geometric volume, not a soil recipe or a weight estimate.
Planter soil ↗
V = πh(D² + Dd + d²) ÷ 12. Diameters D and d are measured inside the planter.
Example: A 30 / 20 cm planter filled to 25 cm holds about 12.435 L. Four pots plus 5% need 52.229 L, or 3 bags of 20 L.
This model assumes a straight-sided circular frustum. Measure the diameter at the intended soil line. Root balls, drainage material and irregular curves are not subtracted automatically.
Plant spacing ↗
Count on each axis = floor((length − 2 × border) ÷ spacing) + 1. The fitted grid is centered.
Example: A 240 × 120 cm bed with 30 cm spacing and 15 cm borders fits 8 × 4 = 32 plants.
This is an aligned grid, not a staggered layout. Choose spacing for your crop and variety; paths and companion planting are not modeled. The preview limits drawn points while preserving the full count.
Mulch coverage ↗
Volume = length × width × layer depth. Buying volume = geometric volume × (1 + allowance).
Example: 5 × 2 m at 5 cm deep uses 500 L. Add 10% for 550 L, or 11 bags of 50 L.
Enter the area actually covered and your chosen depth. Settlement, terrain and material density vary. The calculator does not recommend a depth for a specific plant.
Units and numerical limits
Conversions use 1 inch = 2.54 cm, 1 mile = 1.609344 km, and 1 avoirdupois ounce = 28.349523125 g. Empty, non-finite, out-of-range and unsupported values are rejected. Displayed values are rounded; calculations retain precision. Input-specific limits are reported alongside the field when exceeded.
Raised bed soil guidance · Keter ↗