Choose a pot shape, enter dimensions, then press Calculate. Dimensions can be entered in mm, cm, or inches.
| Date/Time | Shape | Inputs | Full volume | Soil/pot | Pots | Total soil |
|---|---|---|---|---|---|---|
| No items yet. Calculate, then click “Add to batch table”. | ||||||
Downloads include the full volume and adjusted soil volume (fill minus drainage). PDF export requires a modern browser.
Use these sample entries to sanity-check your inputs and outputs.
| Container | Shape | Depth | Top diameter / L×W | Bottom diameter | Approx. volume |
|---|---|---|---|---|---|
| Small nursery pot | Round | 18 cm | 20 cm | — | ≈ 5.65 L |
| Tapered planter | Tapered | 30 cm | 32 cm | 22 cm | ≈ 19.26 L |
| Window box | Rectangular | 15 cm | 60×18 cm | — | ≈ 16.20 L |
- Round (cylinder): V = π × R² × H
- Tapered round (frustum): V = (π × H / 3) × (R1² + R1×R2 + R2²)
- Rectangular: V = L × W × H
- Unit conversion: dimensions are converted to centimeters for consistency.
- Liters: 1 L = 1000 cm³
- Soil adjustment: Soil% = Fill% − Drainage% (clamped at 0).
Results are estimates. Real containers may have curves, ribs, or thicker walls.
- Select the container shape that matches your pot.
- Choose the unit you used for measuring your pot.
- Enter depth, then enter diameter(s) or length and width.
- Set fill percentage for headspace and watering room.
- Enter drainage layer percent if using gravel or clay balls.
- Enter number of pots to get total soil volume needed.
- Optionally add bag size and density for bags and weight.
- Click Add to batch table to compare options.
- Use CSV or PDF download buttons to save your results.
If you are buying soil, round up slightly to cover spillage.
Pot Depth to Volume Planning Guide
1) Why depth-based volume matters
Container depth controls root space, watering rhythm, and nutrient buffering. A 20 cm deep pot typically holds enough profile for herbs and compact annuals, while 30–40 cm depths are more forgiving for tomatoes and peppers. More volume means slower drying and steadier temperatures. For instance, a 25 cm deep, 25 cm diameter round pot holds about 12.3 L.
2) Shape changes the result
A round pot behaves like a cylinder, but many planters taper. Tapered pots use a frustum formula, so the bottom diameter has real impact. For example, a 30 cm depth pot with a 32 cm top diameter and 22 cm bottom diameter is about 19.26 L, not the 24.13 L you would estimate from the top diameter alone. Tapered containers often save soil and reduce weight.
3) Units and conversions you can trust
This calculator converts all dimensions to centimeters before computing volume. Key references: 1 L = 1000 cm³, 1 US gallon ≈ 3.785 L, and 1 ft³ ≈ 28.317 L. Converting first reduces rounding errors when you switch between mm, cm, and inches.
4) Fill level and drainage allowance
Few gardeners fill a pot to the rim. Leaving 5–10% headspace helps watering without overflow. If you reserve 10% for a drainage layer, and fill to 90%, the effective soil fraction becomes 80% of the pot’s full volume. This tool applies Soil% = Fill% − Drainage%. Many growers start with 90% fill and 0–10% drainage, then adjust after the first watering.
5) Buying soil: bags, weight, and waste
Bagged mixes are often sold in 10–50 L sizes. A total requirement of 96 L typically means two 50 L bags, with a little extra for spill and settling. For weight planning, common potting mixes range around 0.4–0.8 kg/L depending on moisture and ingredients. A 40 L bag may weigh roughly 16–32 kg. Keep 5–15% extra on hand for top-ups and repotting.
FAQs
1) Should I measure inside or outside dimensions?
Use inside measurements where soil sits. Wall thickness and curves can reduce real volume, so inside dimensions produce a closer soil estimate.
2) My pot is slightly oval. What should I do?
Measure the longest and shortest inside diameters, average them, then use that average as the diameter. This gives a practical estimate for most oval pots.
3) Why does a tapered pot need two diameters?
Tapered planters narrow toward the base. Using both diameters captures that change, preventing overbuying soil when the bottom is much smaller than the top.
4) What fill percentage is realistic for everyday planting?
Many gardeners use 90–95% to leave watering space. For heavy mulching or top dressing, start closer to 85–90% and top up later.
5) Is a drainage layer always recommended?
Not always. Many mixes drain well without a dedicated layer. If you still add one, keep it small (often 5–15%) and ensure the pot has drainage holes.
6) Why might my real soil usage be higher than calculated?
Soil settles after watering, and mixes can compact during filling. Irregular shapes, ribs, and thicker walls also reduce internal volume. Plan a small buffer.
7) Can I use this for water volume instead of soil?
Yes. The full pot volume is a good estimate of capacity. For safe watering, consider fill level and keep room for displacement from roots and mulch.