Calculator Form
Use the responsive grid below. Large screens show three columns, smaller screens show two, and mobile displays one column.
Formula Used
This calculator supports three common basket profiles so gardeners can estimate realistic planting capacity instead of using one generic pot formula.
1) Bowl / Round Basket
Formula: V = πh(3a² + h²) / 6
Here, a is the opening radius and h is the basket depth. This works well for rounded wire baskets with coco liners.
2) Cylinder Basket
Formula: V = πr²h
Here, r is the radius and h is the basket height. This suits straight-sided hanging containers.
3) Tapered Basket / Frustum
Formula: V = (πh/3)(R² + Rr + r²)
Here, R is the top radius, r is the bottom radius, and h is the height. This matches wider-top planters.
Usable Planting Volume
Usable Volume = Gross Volume × Fill % × (1 − Drainage %)
This reduces the geometric basket size to a more practical planting volume.
Buying Allowance
Buy Volume = Usable Volume × (1 + Settling Extra %)
This gives extra mix for settling, topping up, and minor spillage during planting.
How to Use This Calculator
- Select the basket shape that most closely matches your container.
- Choose centimeters, inches, or feet for all measurements.
- Enter the top diameter, basket depth, and bottom diameter when needed.
- Set the fill percentage to reflect how high you want soil.
- Add a drainage allowance if you leave room for liner folds, drainage, or air space.
- Enter extra soil for settling if you want a shopping estimate.
- Adjust density and wet multiplier to estimate hanging weight more accurately.
- Press the calculate button to view the result above the form.
- Use the CSV or PDF buttons to save a copy of the result.
Example Data Table
| Example Basket | Shape | Dimensions | Gross Volume | Usable Volume | Suggested Soil to Buy |
|---|---|---|---|---|---|
| Small porch basket | Bowl | 30 cm top × 18 cm depth | 9.42 L | 7.63 L | 8.55 L |
| Medium herb planter | Cylinder | 35 cm diameter × 18 cm height | 17.32 L | 14.03 L | 15.71 L |
| Large floral display | Tapered | 40 cm top × 28 cm bottom × 20 cm height | 18.35 L | 15.19 L | 17.01 L |
These examples use typical fill, drainage, and settling settings for quick planning.
Frequently Asked Questions
1) Why does usable planting volume differ from gross volume?
Gross volume is the full geometric space inside the basket. Usable planting volume is smaller because gardeners usually leave headspace, drainage space, and room for watering without overflow.
2) Which basket shape should I choose?
Pick bowl for rounded coco-lined baskets, cylinder for straight-sided pots, and tapered for containers that are wider at the top than the bottom. Choose the closest profile for better estimates.
3) What fill percentage is best for flowers?
Many gardeners use 85% to 95%. That range leaves watering space, reduces spillover, and still provides enough root room. Trailing flowers often perform well with around 90% fill.
4) Why add extra soil for settling?
Fresh potting mix settles after watering and planting. An extra 10% to 15% helps cover early shrinkage, minor spillage, and top-up needs during the first few weeks.
5) How accurate is the hanging weight estimate?
It is an estimate based on soil density and a wet-weight multiplier. Plant mass, liner type, water retention, and basket hardware can change the real hanging load.
6) Should I include liner thickness in the dimensions?
Measure the inside planting space whenever possible. If the liner is thick, internal dimensions give a more accurate soil estimate than measuring the outer metal frame.
7) Can I use this for vegetable baskets?
Yes. The volume estimate works for vegetables, herbs, and flowers. Just remember edible crops may need deeper baskets and stronger support because wet soil becomes heavy.
8) What soil density should I enter?
Light potting mixes are often around 0.30 to 0.45 kg/L dry. Heavier or moisture-rich mixes can be higher. Use your bag specification when available.