Container Size Calculator
Undersized pots are the single most common reason container crops disappoint: the roots run out of room, the compost dries out twice a day, and the plant sulks. Choose the crops you want to grow and how many of each, and this calculator gives you the minimum volume, diameter and depth per plant, the litres of potting mix to buy, and how many plants fit in the planter sizes you can actually buy.
Your garden
Results
Total pot volume
54L
14.3 gal
Potting mix needed
59.4L
That is about 2 bags of 50 L compost.
Plants
5plants
Tomato × 2
18 L per plant- Total pot volume
- 36 L
- Minimum pot diameter
- 28 cm
- Minimum soil depth
- 30 cm
- Potting mix needed
- 39.6 L
How many fit in common planters
| Planter | Plants per planter | Planters needed |
|---|---|---|
| 15 cm pot (2 L) | Too shallow | — |
| 20 cm pot (5 L) | Too shallow | — |
| 25 cm pot (9 L) | Too shallow | — |
| 19 L bucket (5 gal) | 1 | 2 |
| 35 cm pot (30 L) | 1 | 2 |
| 40 cm grow bag (50 L) | 1 | 2 |
| 60 cm window box (20 L) | Too shallow | — |
| 1 m trough (45 L) | Too shallow | — |
| 120 × 60 cm raised bed | 2 | 1 |
Basil × 3
6 L per plant- Total pot volume
- 18 L
- Minimum pot diameter
- 20 cm
- Minimum soil depth
- 20 cm
- Potting mix needed
- 19.8 L
How many fit in common planters
| Planter | Plants per planter | Planters needed |
|---|---|---|
| 15 cm pot (2 L) | Too shallow | — |
| 20 cm pot (5 L) | Too shallow | — |
| 25 cm pot (9 L) | 1 | 3 |
| 19 L bucket (5 gal) | 1 | 3 |
| 35 cm pot (30 L) | 1 | 3 |
| 40 cm grow bag (50 L) | 1 | 3 |
| 60 cm window box (20 L) | 2 | 2 |
| 1 m trough (45 L) | 4 | 1 |
| 120 × 60 cm raised bed | 8 | 1 |
Figures are typical averages. Your cultivar, soil and microclimate will shift them, so treat the results as a starting point.
How it works
- 1
Add each crop you plan to grow and the number of plants you want.
- 2
Every crop carries a minimum root volume and a minimum soil depth drawn from standard container-growing guidance.
- 3
The calculator converts that volume into the diameter a round pot needs at that depth, and adds ten percent to the soil total for settling and the rim gap.
- 4
It then checks your selection against common planter sizes, telling you how many plants fit in each and how many planters you would need.
Frequently asked questions
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