# How to calculate the volume of water in a pool? Why is it important to know?

Knowing precisely the volume of water in your pool is the basis for evaluating the cost of filling it, buying the appropriate equipment and accessories as well as for perfectly dosing the treatment products as we will see in more detail. But above all, let’s get out our calculators!

## Calculate the volume of your pool according to its shape

Whatever the shape of the pool, we start by noting its depth mean. If the pool has a sloping (sloping) bottom, simply take into account the greater depth as well as the shallower and calculate the average of the two by first adding them together then dividing the result obtained by 2.

Example: for a pool with a minimum depth of 1.30 m and a maximum depth of 1.90 m, we obtain: (1.30 + 1.90) / 2 = 1.60

1.60 m is therefore the average depth to be taken into account to calculate its volume of water. But for that it remains to know its surface which will then have to be multiplied by the average depth.

If the pool has a flat bottom, no calculation is necessary since its depth is the same from one end of the pool to the other.

### Water volume of a round swimming pool:

The mathematical formula to first calculate the area of ​​a round shaped pool is pi x r²

Example for a round swimming pool with a radius of 2.50 m (the radius being half the diameter) and 1.70 m deep:

• 3,14 x (2,50 x 2,50) = 19,63 m² (superficie)
• 19.63 x 1.70 = 33.37 m3 (volume)

### Water volume of a square pool:

(side x side) x depth

So for a pool with a side of 5 m and an average depth of 2.10 m, the volume is (5 x5) x2.10 = 52.50 m3

### Water volume of a rectangular swimming pool:

(Length x Width) x Depth

That is, for a swimming pool of 9 m by 4.70 m whose average depth is 1.85 m, the volume is (9 x 4.70) x 1.85 = 78.26 m3

### Water volume of an octagonal pool

There, things get tough for some of us. It is therefore necessary to indulge in a little gymnastics of the mind. Note first that an octagon (regular) is made up of 8 triangles. We start by calculating the area of ​​a triangle by multiplying the length of its base by its height and then dividing the result by 2. You should know that this triangle height corresponds to half the length of the swimming pool.

To calculate the area of ​​the pool, the area of ​​a triangle must be multiplied by 8. Finally, the volume of the octagonal pool is calculated by multiplying the total area by the depth of the basin.

Example for an octagonal swimming pool with a depth of 2.15 m, each triangle base measuring 0.80 m and its height 1.20 m, we obtain [(0,80 x 1,20) / 2) x 8] x 2,15 = 8,25 m3

Finally, it should be remembered that 1 m3 = 1,000 litres. We multiply the number of m3 by 1,000, which gives us, for example, 21,000 liters for 21 m3.

## Pool water volume: a crucial parameter

This data must be known to the owner because it is fundamental at different levels. Indeed, it is better to know precisely the volume of water in your pool when you are about to buy equipment, accessories and treatment products. Small useful precision: whatever the shape of the swimming pool, it is recommended toround up the result obtained. For example, for a volume of 42.56 m3, we round up to 43 m3.

• A cleaning robot : it comes in different models and variable power. It is necessary to know the volume of your pool to buy a suitable robot. If it must be powerful for a large pool, it is not necessary to get a behemoth for a small pool.
• A filtration system : 80% of the water is cleaned by this device. To be able to swim in a purified water and which circulates correctly, it is essential to install a sufficiently powerful pump since its role is to suck up the water so that it passes through the filters then to push it back towards the basin once it is clean. Note that to choose the pump of the filtration system adapted to your swimming pool, the main criterion to consider is its flow rate. It is expressed in m3/h.
• A heater : the choice of the heating system is also based on the volume of water and it is logical because if it is too low in power, it will not be able to heat all the water in a large swimming pool and the swimming may not be very pleasant.
• Treatment products : they complement the action of the filtration system and must be precisely dosed. In excessive quantities, these treatments can be irritating or cause an allergy, therefore dangerous for people who bathe. On the other hand, if the dosage is too low, the water will not be of good quality because it is poorly balanced, which can also cause health problems. In addition, insufficient treatment promotes the colonization of water by algae (it then becomes green) or by bacteria.

Finally, the estimate of filling cost also involves knowing the volume of your swimming pool, the water being invoiced by the supplier per m3. This rate varies significantly from one region to another. If we evaluate this rate at €3.50/m3, filling a 30 m3 swimming pool costs €105 and that of a 17 m3 swimming pool costs €59.50. But this weighs little on the budget because it is not necessary to change all the water in your swimming pool every year. At most, it should be partially renewed.