Flower boxes for the balcony are available in different lengths. As a result, the amount of potting soil required also varies. If you don't want to buy too much soil, you should be able to calculate the contents of a flower box.
How many liters of potting soil does a flower box need?
The amount of potting soil required for a flower box depends on its size and shape. Standard 80 cm long flower boxes require around 18 liters, wider models around 25 liters and 1 m long boxes with water storage around 24 liters of potting soil.
Calculating the volume of a flower box
Anyone who owns a computer has a clear advantage here. The Internet offers so-called “soil volume calculators” on various sites, for example for rectangular planters. You only need the following information for the automatic calculation:
- Length at the top of the vessel in cm
- Width at the top of the vessel in cm
- Length at the bottom of the vessel in cm
- Width at the bottom of the vessel in cm
- Length of the inside height in cm
Using this information, the computer automatically calculates how much potting soil is needed for the box.
Calculate the volume yourself
Flower boxes have a variety of shapes. The trapezoidal shape is common, but cuboids or cubes are also possible. In order to calculate the volume of the shapes, the mathematical formulas are necessary.
Calculate volume for the trapezoid shape
To do this, measure the top width of the box (the distance a), the width of the bottom (the distance b) and the height h. The last thing you need is the total length of the box c. Then use the formula [(a + b):2)] x h x c to calculate the volume in cm³. 1000 cm³ is 1 liter.
Calculate the volume of the cuboid
This is quickly calculated with the values for length (a), width (b) and height (c), as well as the formula a x b x c, also in cm³.
Calculate the volume of the cube
Since all sides (a) of the cube are the same length, you calculate a³ or a x a x a. The result is again cm³, which can easily be converted into liters.
Tip
If you don't want to go to the trouble of calculating the volume of the flower box yourself, you can use the following estimates:
- the usual flower box (€56.00 on Amazon) about 80 cm long requires about 18 liters of potting soil
- The slightly wider, equally long box requires approx. 25 liters of soil
- The boxes with water storage are 1 m long and require approx. 24 liters of soil to fill them
