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Potting soil calculator

Estimate potting mix for rectangular planters and tapered round pots, then convert it into bags to buy.

On your device · No sign-up
LIVE ESTIMATE

Potting mix

Your garden measurements

Use inside measurements. Results update automatically.

Units
Shape
Use the volume printed on the product bag.
Optional extra material, from 0 to 100%.
Shopping summary

Ready for the garden center

4bags to buy

20 L / bag · 5% extra allowance

Space to fill64.21 L
Including allowance67.42 L
Volume in whole bags80 L
Extra after allowance12.58 L
0.064 m³0.084 yd³0.29 m²
Estimated material cost

Add a bag price to see the budget.

Calculated on your device. No signup or uploads.

How this is calculated

π × depth × (top² + top × bottom + bottom²) ÷ 12 × quantity. Add your allowance, divide by one bag’s volume, then round up to whole bags.

The round pot calculation uses a conical frustum. A rectangular planter is treated as a straight-sided box. Root balls, drainage inserts and existing soil reduce the amount of new mix needed; subtract their volume separately.

A LITTLE GUIDANCE

Less effort. Clearer results.

01 / Potting mix

Potting soil calculator

  1. Choose a rectangular planter or a round pot. Measure the inside dimensions in centimeters or inches.
  2. For a tapered round pot, enter its top diameter, bottom diameter and the depth you will fill. Enter the number of matching pots.
  3. Set your potting mix bag size and optional price. Copy the live shopping list or download it for your trip.

The round pot calculation uses a conical frustum. A rectangular planter is treated as a straight-sided box. Root balls, drainage inserts and existing soil reduce the amount of new mix needed; subtract their volume separately.

Open dedicated tool ↗

FAQ

A few useful things to know.

Why enter two diameters for a round pot?

Many pots narrow toward the bottom. Using only the top diameter overestimates the mix. Top and bottom diameters give a more realistic tapered-container estimate.

What if my pot has straight sides?

Enter the same top and bottom diameter for a round straight-sided pot. For a rectangular straight-sided planter, select the rectangular option.

Does the estimate include a plant’s root ball?

No. It estimates the empty container volume to your chosen fill depth. Existing soil and the root ball take up space, so you may need less new mix.