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, a 24" round planter of basil:
- Floor area: π × 12² = 452 sq in
- Basil spacing: 9" apart, so area per plant: 9 × 9 = 81 sq in
- Plants: 452 ÷ 81 = 5 basil plants
That is the calculation the tool runs. Pick what you are planting and it applies the matching spacing from the table above.
Soil volume matters: container soil dries out far faster than ground soil, because the whole root ball is surrounded by warm air rather than insulated by earth. Heat compounds it quickly, and a pot that needed water every other day in spring can need it twice daily in a midsummer heatwave. Water-retaining crystals or a self-watering insert are worth it on a hot balcony.
One caveat on volume: the arithmetic treats a pot as a straight cylinder. Almost none are. A typical tapered pot holds 20 to 30 percent less than the cylinder figure, so buy to the number here and you will have a little spare rather than a pot you cannot finish filling.
How we build and check this calculator
This calculator runs entirely in your browser, so the numbers you enter stay on your device. The math behind it is written by hand and tested against worked examples and standard references before the page goes live.
SuperGlobalCalculator is independently built and maintained. See how we build and verify our calculators.