Formula used
Rectangular planter: V = L × W × H.
Cylindrical planter: V = πr²H.
Tapered rectangular planter: volume integrates the changing rectangular area through the fill height.
Tapered round planter: V = πH(R² + Rr + r²) ÷ 3.
Adjusted purchase: net soil volume × compaction allowance × waste allowance.
The calculator separates drainage, mulch, and displaced space. Existing soil reduces the purchase quantity. Bag totals always round upward.
How to use this calculator
- Select the planter shape and measurement basis.
- Enter the dimensions using one consistent length unit.
- Add drainage, mulch, and displacement values.
- Choose bag size, density, moisture, and cost assumptions.
- Optionally create a soil mixture totaling 100%.
- Calculate, review, copy, print, or export results.
Example data
| Planter | Dimensions | Layers | Suggested use |
|---|---|---|---|
| Rectangular raised bed | 4 ft × 2 ft × 1.5 ft | 0.15 ft drainage, 0.1 ft mulch | Vegetables and herbs |
| Round planter | 2 ft diameter × 1.5 ft high | 0.1 ft drainage | Small ornamental tree |
| Tapered box | 4 × 2 ft top, 3.5 × 1.5 ft bottom | 10% compaction | Patio flowers |
Frequently asked questions
1. Should I enter inside or outside dimensions?
Inside dimensions give the most direct volume result. Outside dimensions require wall and bottom thickness values. Measure carefully before purchasing materials.
2. Does the calculator subtract the drainage layer?
Yes, it calculates drainage separately from soil capacity. Tapered planters use changing cross-sectional dimensions. This improves layer volume accuracy.
3. Why is mulch excluded from soil volume?
Mulch occupies space near the planter surface. Excluding it prevents buying excessive soil. Enter zero when mulch is unnecessary.
4. How are tapered planters calculated?
The calculator models dimensions changing through the planter height. It also measures partial drainage and mulch layers. Results remain consistent across supported units.
5. Why are bag quantities rounded upward?
Stores normally sell complete bags only. Rounding downward would create a material shortage. Surplus volume is shown separately.
6. What compaction allowance should I use?
Loose mixes often settle after watering. Ten percent is a practical starting estimate. Actual settlement depends on material structure.
7. Can I calculate several identical planters?
Yes, enter the total planter quantity. Volume, bags, weight, and cost multiply automatically. Per-planter cost remains visible.
8. Must the soil mixture total 100%?
Yes, active mixture percentages must total 100%. Leave every percentage at zero otherwise. The overall density then estimates weight.
9. Are weight estimates exact?
No, soil weight changes with moisture and compaction. Density values are planning assumptions only. Check structural limits for balconies.
10. How does existing soil affect results?
Existing soil reduces the new purchase requirement. Enter its volume for each planter. Excess existing volume triggers a warning.
11. Can results be exported?
Yes, results can be copied or downloaded. CSV supports spreadsheet analysis and records. PDF creates a printable project summary.