Measuring a Water Tank for a Replacement Liner

water tank dimensions-roundA water tank liner is a great way to extend the life of a water tank that is still structurally sound but leaks water. Tank liners also have the added benefit in that further leaks are usually prevented as there is now a permanent membrane between the water any potential spot where a leak may form due to rust, cracking or ground movement.

Typical residential water tanks come in one of two shapes. Either they are circular or they are rectangular with rounded ends.

Making a tank liner for a round water tank is a fairly straightforward process. The only complication is if there are structural supports. These can be accommodated for, but the liner will have to be installed by a professional who can weld the liner around the struts.

With slimline and other similarly shaped water tanks, the process is only slightly more complicated in that the end shape has to be measured properly.

Other shaped water tanks are usually specialty water tanks and should be inspected by a qualified installer.

Measuring Any Round Water Tank

All that is needed to work out the size of the tank liner is the internal diameter (d) of the tank and the height (h) of the inside of the tank.

You can also use these measurements to calculate the volume of your water tank. This example assumes you are measuring in meters.

Calculating the volume of your water tank:

π x (d/2) x (d/2) x h   where π is pie = 3.14159

so for a 2 m high tank with a diameter of 5 m, the volume is them

= 3.14159 x (5 ÷ 2) x (5 ÷ 2) x 2 = 39.27 m3

The amount of water that can be held is then 39.27 x 1000 = 39,270 litres

Measuring a Rectangular Water Tank, eg a slim line Water Tank

Slim line Water Tanks are a little more difficult to measure, but not too much. To work out the size exactly, you just need to take into account the flat middle section and then both rounded ends. Each end of the water tank is like a semi-circle. I will assume each end is the same as this is usually the case.

water tank dimensions-slimline

To measure you need:

h – height

d – width of flat middle section

a – width of water tank

b – distance from flat section to end of tank

volume is then:

2 x area of end pieces plus area of middle section

2 x π x (a/2) x (b) x h + a x d x h   where π is pie = 3.14159

so for a 1.8 m high tank, with a flat section that is 2 m long, is 800 mm wide and b is 500 mm.

2 x 3.14159 x (0.8 ÷ 2) x 0.5 x 1.8 + 1.8 x 2 x 0.8

2.26 m3 + 3.4 m3 = 5.66 m3

This means the volume of water that can be held is 5660 litres.

Liner and Pool Cover Material Thickness

Depending on where you are from you will have heard the terms mil, micron and millimetres to describe the thickness of pool, dam and pond liners as well as Pool Covers. Mil is an imperial US term, micron is a technical term that has been in use for a number of decades and millimetre is the proper metric way of stating a material thickness.

 A simple ratio exists between them all:

 1 Mil = 1/1000th of an inch = 0.0254 mm

1 micron is 1/1000 of a millimetre (mm)

 Where did these terms come from? Some interesting History

Mil:- The use of Mil as equalling 0.024 inches in measuring and engineering was first used by Henry Ford as a better, consistant measuring system for his car parts. The Swedish inventor Carl Edward Johansson actually chose the relationship as it allowed switching between metric and imperial threads in a lathe by using wheels with 100 and 127 cogs on them. At this point in history there were many different “inch” lengths, and the development of the “standard inch” ended up taking about 30 years. The mil terms remains a purely American engineering term.


Metre and Millimetre:- The origin of the SI unit metre began in 1668 when the English cleric and philosopher John Wilkins proposed a decimal based unit of length. On the 27th of October 1790 the French Academy of Sciences suggested a basic unit of length equal to one ten-millionth of the distance between the North Pole and the Equator, to be called the metre. The first occurrence of metre in this sense in English dates to 1797.

Over the decades, this definition has been refined so now the current definition of a metre (or meter if are in the US) is the length that light will travel in a vacuum in 1/(299 792 458) of a second.

Ok, enough of the nerdy stuff, so you have for example a 500 micron pool liner, what does this really mean? Using the above ratios, 500 microns is simply 0.5 mm or 20 mil

The Thickness of Pool Covers

The thickness of a pool cover is usually measured in microns, and does not include the bubble height. Common pool cover thicknesses are 250, 400, 500 and 600 microns. Typically the thicker the material, the longer it can withstand the Australian sun, but the heavier it will be.

The Thickness of Pool Liners

Pool liners are usually measured in mm, and the recommended thickness for an inground pool liner is 0.75 mm. For an above ground pool, 0.5 mm is the recommended thickness. While it is possible to buy thicker liners, remember that these are not always better as the tracking used to hold the liner in is usually only designed for a specific thickness. Becareful if you go thinner, this is because the material has to stretch into place, and below these thicknesses the material might become too thin where it stretches and is more likely to fail.

For More Information Visit:- Pool Liners