Grow Bag Soil Volume Calculator
Calculate how much potting mix you need to fill grow bags by size and quantity — in liters, cubic feet, or bags of soil.
Soil Volume Needed
Grow Bag Soil Volume Guide
Grow bags are fabric or plastic containers used for growing vegetables, herbs, and flowers in small spaces. They come in a wide range of sizes, and knowing how much potting mix to buy saves money and avoids waste.
Common Grow Bag Sizes and Uses
| Size | Volume | Best For |
|---|---|---|
| 1 gallon (3.8 L) | 3.8 L | Herbs, small greens |
| 3 gallon (11 L) | 11.4 L | Peppers, compact tomatoes |
| 5 gallon (19 L) | 18.9 L | Standard tomatoes, cucumbers |
| 7 gallon (26 L) | 26.5 L | Large tomatoes, eggplant |
| 10 gallon (38 L) | 37.9 L | Fruit trees (dwarf), large vegetables |
| 15 gallon (57 L) | 56.8 L | Dwarf fruit trees, large shrubs |
| 20 gallon (76 L) | 75.7 L | Trees, large planters |
| 25 gallon (95 L) | 94.6 L | Blueberries, multi-plant setups |
Fill Factor
Grow bags should be filled to about 85–90% of their rated volume. This accounts for soil settling and leaves room for watering without overflow. The calculator applies a 0.87 fill factor by default.
Choosing the Right Potting Mix
- Fabric grow bags — Use a light, well-draining mix. Heavy garden soil compacts and reduces yield.
- Standard potting mix — Works for most vegetables.
- Coco coir blend — Excellent drainage, ideal for fabric bags that dry out faster.
- Perlite ratio — Add 20–30% perlite to any mix for extra drainage and aeration.
Watering More Frequently
Grow bags lose moisture faster than ground soil or hard-sided containers. In hot weather, fabric grow bags may need watering once or even twice daily. Consider sub-irrigation or a drip system for large setups.
Commercial Soil Bag Sizes
| Bag Size | Volume |
|---|---|
| Small bag | 10 L (0.35 cu ft) |
| Medium bag | 25 L (0.88 cu ft) |
| Large bag | 40 L (1.4 cu ft) |
| Cubic foot bag | 28.3 L (1 cu ft) |
| 2 cubic foot bag | 56.6 L (2 cu ft) |