Dial in fabric pot capacity before planting day. Choose shape, units, and fill percentage easily. Know liters, gallons, and bag counts with confidence today.
| Scenario | Shape | Dimensions | Fill | Headspace | Compaction | Estimated Purchase |
|---|---|---|---|---|---|---|
| Tomatoes | Round | D 35 cm, H 35 cm | 95% | 2 cm | 10% | ~30–35 L |
| Herbs mix | Rectangular | L 60 cm, W 30 cm, H 25 cm | 90% | 3 cm | 8% | ~35–40 L |
| Peppers | Tapered | Top 40 cm, Bottom 28 cm, H 30 cm | 100% | 2 cm | 12% | ~30–38 L |
Grow bags rarely match the labeled size because fabric flex changes the filled geometry. Measuring the filled diameter and soil height improves consistency across plantings. Accurate volume planning reduces nutrient swings, prevents under-filled root zones, and keeps irrigation schedules predictable across beds and containers.
Headspace lowers effective height so water and mulch do not spill. A drainage layer reduces soil capacity while improving aeration. Fill percentage reflects how firmly you pack media. Compaction allowance covers settling after the first few waterings, transplant vibration, and organic mix shrinkage.
Liters are standard for potting mixes, while gallons are common on bag labels. Cubic feet helps when buying bulk compost or blended soil by volume. Use the purchase volume, not the raw volume, for shopping because it includes your fill and compaction assumptions.
For airy mixes with coco coir or bark, 8–15% compaction allowance is typical. Dense mineral-heavy blends can use 3–8%. Headspace is often 2–5 cm (or 1–2 inches) depending on watering style. If you bottom-water, a slightly larger headspace may be useful.
Example: Round bag, D 35 cm, H 35 cm, headspace 2 cm, fill 95%, compaction 10% produces a purchase volume near the low-to-mid 30-liter range. With 50-liter bags, you typically need 1 bag per container; with 25-liter bags, plan for 2. When mixing amendments, reserve 10–20% of the purchase volume for compost, perlite, or slow-release components so the final blend still meets the target liters.
Measure when filled or at least shaped, because fabric sides bulge and change diameter. Using filled measurements makes the computed liters much closer to what the container actually holds.
It accounts for settling after watering and handling. Light mixes shrink more than dense blends. Adding 8–15% often prevents running short of mix during final top-ups.
Enter the thickness of coarse material placed at the bottom. The calculator reduces usable soil volume accordingly, helping you purchase the correct amount of planting medium.
Select the tapered option and enter top diameter, bottom diameter, and height. This captures the sloped sides better than a cylinder and improves the estimate for fabric pots.
Purchase volume includes compaction allowance for settling. Usable soil volume reflects what remains after fill percentage and drainage reduction, but without extra material for later top-ups.
Use the purchase liters and the bag count estimate. If your mix contains large amendments, consider buying slightly more so your final blended volume still matches the target.
Yes. Run the calculator for each set of dimensions and keep the same allowances. The CSV or PDF export helps you store results and compare containers consistently.
Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.