Calculation Results
Your planter calculation appears here.
Formula and calculation breakdown
Saved calculation history
Formula used
A rectangular planter uses length multiplied by width and usable height. A cylinder uses π multiplied by radius squared and height. Tapered planters use frustum formulas to reflect changing side dimensions.
A spherical-cap bowl uses its top radius and measured depth. External measurements are reduced by wall and base thicknesses. Soil, drainage, mulch, and rim space are calculated separately.
How to use the calculator
- Select the planter shape and measurement units.
- Enter internal dimensions, or choose external measurements.
- Add rim space, drainage depth, mulch, and settlement.
- Select bag size, soil mix, price, and density.
- Calculate, review the breakdown, then export results.
Example planter capacities
| Planter | Shape | Dimensions | Capacity | Approximate bags | Suggested use |
|---|---|---|---|---|---|
| Window box | Rectangular | 60 × 20 × 18 cm | 21.6 L | 1 × 25 L bag | Herbs, annual flowers |
| Patio pot | Cylinder | 40 cm diameter × 38 cm | 47.8 L | 2 × 25 L bags | Tomatoes, shrubs |
| Raised bed | Rectangular | 1.2 × 0.6 × 0.3 m | 216 L | 5 × 50 L bags | Vegetables, mixed planting |
| Tapered planter | Round frustum | 45/30 cm diameters × 40 cm | 44.8 L | 2 × 25 L bags | Small trees, ornamentals |
| Half-sphere bowl | Spherical cap | 50 cm diameter × 20 cm | 18.6 L | 1 × 20 L bag | Succulents, shallow roots |
Frequently asked questions
Should I measure inside or outside?
Internal dimensions provide the most direct usable-volume estimate. External dimensions require wall and base thickness deductions.
How much space should remain below the rim?
Many planters work well with two to five centimetres. This space helps watering without immediate overflow.
Does a drainage layer reduce soil volume?
Yes. The calculator separates drainage volume from the soil-filled section.
Why add settlement allowance?
Potting mixes often settle after watering. Extra material helps maintain the intended finished level.
How are tapered planters calculated?
The calculator integrates changing cross-sections through the planter height. This is more accurate than averaging diameters casually.
Can I calculate several identical planters?
Yes. Enter the quantity, and all soil, bag, cost, and weight results scale automatically.
Can I include different planter sizes?
Yes. Add known net capacities in the additional planter groups table.
How does the soil mix section work?
Each ingredient receives its percentage of the adjusted purchase volume. Percentages should total exactly 100%.
Are bag totals rounded upward?
The default mode rounds to whole bags. Half-bag and exact-display options are also available.
Is the filled-weight estimate exact?
No. Moisture, compaction, and real material density can change the final weight significantly.
Can I save or export results?
Yes. Results can be copied, printed, downloaded as CSV or PDF, and stored in browser history.