Potting Soil Calculator

Created by Hanna Pamuła, PhD
Reviewed by Bogna Szyk and Adena Benn
Last updated: Nov 15, 2022

This potting soil calculator allows you to measure the volume of soil needed for your container. Whether you want to have a raised bed in your garden or rearrange your blooming balcony, use the calculator to estimate how much soil you need to prepare. Choose from three types of containers, calculate your needs, then go ahead and start your garden!

Container shape

There are many different container types on the market. In our potting soil calculator, you can select between three different shapes. It finds the volume according to the formulas below:

  • rectangular - e.g., raised bed soil containers

    volume of rectangular cuboid: volume = depth × length × width

  • round

    volume of a cylinder: volume = π × R² × depth , where R is a radius

  • flower pot in the shape of a truncated cone

    volume of a truncated cone: volume = (1/3) × π × depth × (r² + r × R + R²), where r is a radius of the base of flower pot, and R of top surface radius

If you want to estimate the weight or cost of topsoil, use our soil calculator.

How much soil do I need?

Let's imagine that you want to grow herbs. You have a couple of small flower pots, and you don't know how much soil you need. This potting soil calculator can help with that problem:

  1. Choose the shape of the container.
    In our case, it's a flower pot, so we need to calculate the volume of the truncated cone.
  2. Enter the dimensions.
    For example, assume we have pots with a diameter across the top equal to 4 inches, a bottom base diameter of 3.2", and a height of 2.75". Don't forget that you can select different units, such as centimeters, feet, etc.
  3. Set the quantity of the flower pots.
    We want to plant oregano, basil, and thyme, so we need to put three in the quantity field.
  4. The volume of soil required is equal to the displayed value.

Our calculator is a flexible tool, so you can calculate everything the other way round: if you have a bag of soil and the size of your containers, you can estimate how many pots can be filled.

Remember that the obtained result represents the volume for the full container. Sometimes you want to fill the container to 4/5, or you already have a plant or tree with the roots, and then you will need less soil. The amount of soil may also change as you squeeze it or leave it looser, so the presented calculations are only a good estimate.

Are you interested in other agricultural calculators? Check out our vegetable seed and fertilizer calculators.


How do I determine the amount of potting soil I need?

The amount of potting soil you need is determined using the volume of the pot.

It depends firstly on the shape of the pot you are using and then how much you want to fill it. Whether you compress the soil in the pot or keep it loose will also impact the amount needed.

How can I calculate potting soil for my terrace garden?

We can use the potting soil formula to estimate your needed soil.

  1. First, you need to get the dimensions. Let's assume you are using rectangle pots, 5 of them, to be precise. The dimensions of these pots are 24 cm, 18 cm, and 10 cm in length, width, and depth.

  2. Using the formula:
    Soil = Volume of pot × Number of pots
    Soil = Length × Width × Depth × Number of pots

  3. Substitute in the known values: Soil = 24 × 18 × 10 × 5

  4. So: Soil = 21.6 liters.

How much soil do I need for my 30 cm round pot?

The formula to determine the soil needed for a round pot uses the volume of a cylinder.

So, if 30 cm is the radius and assuming the depth is 10 cm, the amount of potting soil needed is:

Soil = π × Radius² × Depth

Soil = 3.14 × 30² × 10

Soil = 7 liters

Can I have a pot of any shape for my garden?

In theory, yes, you can have a pot of any shape for your garden and soil it to plant any plant of your choice.

Make sure the shape is plant friendly and allows room for the roots to expand. Also, if you need to estimate the amount of soil you would need for your pot, then you would need the formula for the volume of the shape you decide to use.

Hanna Pamuła, PhD
US qt
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