Estimate potting soil volume for a round pot or a rectangular bed, and convert NPK label percentages into grams of product for your planting area — results update as you type.
Cylinder (round pot) or rectangular bed. Use internal dimensions in centimetres.
Container shape
Default 50 L — typical retail bag.
Cylinder: V = πr²h, r = diameter ÷ 2.
1 L = 1000 cm³.
Box: V = length × width × depth.
1 L = 1000 cm³.
Enter the area and either a target rate for one nutrient from the label, or a ready-made product rate in g/m².
Label analysis (N–P–K)
Use guidance for your crop or a soil test recommendation.
Mass of finished fertilizer per square metre.
Product mass = area × (g/m² of nutrient) ÷ (nutrient % ÷ 100).
Label numbers are mass % of N, P₂O₅, and K₂O.
Total grams = area (m²) × rate (g/m²).
Rules of thumb for one mature plant in a pot; climate and variety may change needs.
| Plant | Suggested volume |
|---|---|
| Bigleaf hydrangea | 10–20 L |
| Tomatoes (determinate) | ~15 L |
| Bell pepper | 8–12 L |
| Strawberry (one plant) | 5–10 L |
| Patio rose | 15–25 L |
| Young citrus | 20–40 L |
| Lavender | 10–15 L |
| Leaf lettuce | 3–5 L |
Use the Soil tab above to turn your pot or bed dimensions into litres and bags.