Potting Soil Calculator

How Much Potting Soil Do You Need?

Whether you are filling raised garden beds, planting herbs in containers, or repotting houseplants, knowing exactly how much potting soil to buy saves you time, money, and hassle. Our potting soil calculator estimates the volume of soil needed for any container shape, and even calculates how many bags to buy.

Potting Soil Formulas by Container Shape

The amount of soil you need depends on the shape of your container. Here are the volume formulas for the three most common container shapes:

Rectangular container (raised beds, window boxes): $$V = L \times W \times D$$ where $L$ is length, $W$ is width, and $D$ is depth.

Round / Cylindrical container (standard pots): $$V = \pi \times R^2 \times D$$ where $R$ is the radius (half the diameter) and $D$ is depth.

Tapered flower pot (truncated cone shape): $$V = \frac{1}{3} \times \pi \times D \times (r^2 + r \times R + R^2)$$ where $R$ is the top radius, $r$ is the bottom radius, and $D$ is the depth.

The total soil needed is simply the per-container volume multiplied by the number of containers: $$V_{total} = V_{container} \times N$$

How to Use the Potting Soil Calculator

Select your container shape from the dropdown: rectangular, round, or tapered flower pot. Enter the dimensions in your preferred unit (centimeters, inches, feet, or meters). Specify how many containers you have, and the calculator instantly shows the total soil volume required. Enable the "Calculate bags needed" option to enter your bag size and find out exactly how many bags to buy.

For example, if you have 3 rectangular pots measuring 40 cm x 20 cm x 15 cm each, you need 36 liters of soil. If potting soil comes in 10-liter bags, you will need 4 bags.

Tips for Buying Potting Soil

Soil volume can vary depending on how compacted it is. When filling pots, leave about an inch of space below the rim for watering. It is also a good idea to buy slightly more soil than the calculator suggests to account for settling and compaction. Our calculator gives you a solid estimate to start with.

For garden beds, use the Raised Bed Soil Calculator to get precise soil estimates, or plan your garden coverage with the Mulch Calculator.