Container Garden Calculator
Calculate how much potting soil you need and how many plants fit in your container.
Enter pot diameter and depth for accurate results.
Container garden planting density determines whether your plants thrive or compete for water, nutrients, and light. Overcrowding is the most common beginner mistake and leads to poor yields and disease.
Plants per container formula:
Plants per Container = Floor Area of Container / Recommended Spacing Area per Plant
Floor Area = π × (diameter/2)² for round pots; Length × Width for rectangular
Minimum container depth by plant type:
| Plant Type | Min Depth | Min Diameter |
|---|---|---|
| Lettuce, herbs | 6" | 6" |
| Radishes, green onions | 8" | 8" |
| Peppers, bush beans | 12" | 12" |
| Tomatoes (determinate) | 18" | 18" |
| Tomatoes (indeterminate) | 24" | 24" |
| Cucumbers, squash | 18" | 24" |
| Root vegetables (carrots) | 18" deep | 12" |
Planting spacing reference:
| Vegetable | Spacing in Containers |
|---|---|
| Lettuce | 6–8" apart |
| Basil | 8–10" apart |
| Spinach | 4–6" apart |
| Cherry tomato | 1 per 15–20" pot |
| Pepper | 1 per 12–14" pot |
| Kale | 8–12" apart |
| Strawberry | 8–10" apart |
Worked example — 24" round planter for herbs:
- Floor area: π × 12² = 452 sq in
- Basil spacing: 9" apart → area per plant: 9 × 9 = 81 sq in
- Plants: 452 / 81 = 5–6 basil plants
Soil volume matters: Container soil dries out faster than in-ground soil. Every 10°F above 70°F roughly doubles watering frequency. Add water-retaining crystals or a self-watering insert for balcony gardens in hot climates.