Grow Bag Soil Volume Calculator
Calculate how much potting mix is needed to fill grow bags by size and quantity.
Returns volume in liters, cubic feet, and standard 1 and 2 cubic foot bags.
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) |