During the construction of a water supply system, septic tank or gas pipeline, it is necessary to calculate the volume of water of the filled pipeline. This indicator will help to choose the right expansion tank, the capacity of which should be no more than 10% of all the water in the pipes. In the labeling of products, dimensions can be indicated in inches, therefore, before calculations, they are converted to centimeters.
Why you may need to calculate the water in the pipe
In the water supply system of a private house there are a pipe line, radiators, a liquid reservoir - a membrane tank, as well as boilers, a boiler and other devices. The heat-insulated floor is a system of a laid-out metal-plastic line containing a heat carrier in a certain volume. To completely fill the system and know how much to buy distilled water, you need to calculate its total volume in advance.
When filling the heating system with antifreeze or other non-freezing liquid, in order to save, it is necessary to know the volume of the pipe. When buying concentrated antifreeze, it will need to be diluted in half, so a larger amount of liquid will cost more, and the concentration will not be calculated correctly.
When calculating the volume is used:
- inner diameter of pipe walls;
- the length of the section or the entire trunk.
In case of a difference in the internal section, each section is calculated separately and then the numbers are added up.
In addition to the trunk, the internal volume of the following devices must be taken into account:
- Membrane tank. This information can be read in the technical passport or checked independently, pouring a certain amount of liquid into it.
- Radiators. These data are also in the product passport. The volume of one section is multiplied by their number throughout the house.
- Various units, complex wiring, collectors also contain a certain amount of liquid, which is difficult to calculate due to the large number of fittings, adapters, taps.
The third indicator is usually not taken into account, since this amount is considered an error and does not particularly affect the operation of the plumbing and heating system.
For sewage
It is important to calculate the amount of water in the pipe and the potential of the main line when installing a septic tank, since a lack of diameter can lead to poor outflow of fluid from the house and clogging of the sewer. If the number of household appliances in the house for water consumption exceeds the capacity of sewer pipes, the liquid will fill the line completely. If they are not insulated at the same time, in winter it is possible to freeze the drains inside and block the trunk. An ice plug can also provoke a pipe rupture in a weak place, for example, at joints or sharp turns. The volume of cast-iron sewer pipes should be greater, since the cast-iron surface is rough from the inside and silt is gradually accumulating in it - a layer of organic matter that narrows the clearance and affects the throughput of the main. Plastic pipes are better in this respect - they are perfectly smooth inside, organic particles cannot attach to the walls, so the estimated volume can not be increased further.
The volume of the internal sewer pipes should not be larger than the external highway. This leads to blockages in the area where the inner and outer sewer pipes meet. The same principle applies for internal wiring - the volume of liquid from household appliances should not exceed the volume that the main riser in the house can accommodate.
For well
It is important to calculate the volume of fluid in the well, since its flow rate (productivity) should provide the desired volume per unit time, otherwise household appliances will work poorly. It is necessary to take into account the number of taps in the house - each of them can dispense half a cubic meter of liquid in an hour. The volume of the well is taken into account when selecting the pump capacity - if the flow rate is less than the capacity of the pumping station, it will pump out water completely. So you can put the equipment into disrepair. According to the rules, the power of the pump should not exceed the flow rate of the well.
The flow rate can change depending on the time of the year: in summer there is less fluid if the well is fed from the overhead; less changes if the pipe is laid in groundwater and practically does not change if the drilling was carried out on limestone - a deep artesian well.
How to correctly calculate the volume of water in a pipe
When calculating, it is recommended to independently check the dimensions of the inner cross section of the pipes using a caliper. If the measuring device is not designed to measure the internal diameter, then the external and wall thickness are measured separately, and then the smaller is subtracted from the larger - this will be the desired number. It must be used in the calculation formula. The fluid volume is calculated using the following numbers:
- r is the radius of the inner circle, the diameter is divided by 2;
- the number π (pi) is a constant mathematical value, which is the ratio of the circumference of a circle to its diameter and is 3.14;
- 100 cm - the length of the pipe section for which the calculation is carried out, you can take a different value.
The volume is calculated in cubic meters by the formula: V = 100 x πr2. Using the same formula, the internal volume of a septic tank of a cylindrical shape or a membrane tank can be calculated.
To convert the length of the section of the water pipe to liters, you need to multiply the volume by 1000, since in 1 cubic meter 1000 liters of water. The weight of water in a pipe of 1 cubic meter is 1 ton.
When calculating the actual indicators, it must be borne in mind that the throughput of the pipe also depends on the material from which it is made. For example, plastic products have a large throughput, and steel products are an order of magnitude smaller due to the presence of roughnesses inside. Therefore, calculations are done for each section separately, if they are made of different materials.
Another important indicator is the unit of measurement. Two are used in pipe rolling: in millimeters and inches. An inch is 25.4 mm or 2.54 cm.
Pipe size chart in inches / millimeters:
| Pipe size in inches | External diameter | Inner diameter |
| 1 | 33,5 | 25 |
| 3/4 | 26,8 | 20 |
| 1/2 | 21,3 | 15 |
| 3/8 | 17 | 10 |
| 1/4 | 13,5 | 8 |
| 2 | 60 | 50 |
| 3 | 88,5 | 80 |
If it is only planned to build a water supply, calculations are carried out in advance in order to compare them with the pump capacity and well flow rate, as well as the volume of sewer pipes.
When the water supply system is already in operation and there is a need, for example, to increase the septic tank, you can use the table, which without a calculator gives the exact value of the volume. In this case, it will be possible to measure only the outer diameter, although it is precisely the inner diameter that is needed to calculate the amount of liquid in the pipes. To do this, take the average wall thickness of the plastic or metal pipe based on its diameter and subtract from the size of the outer diameter. You can get the volume per 1 meter. If the highway is long, at 10 or 100m. These calculations are relevant for underfloor heating, where metal-plastic or copper pipes are laid close to each other.
Table of the ratio of the inner diameter and volume of the liquid in liters:
| Inner diameter | In 1 meter | 10 m | 100 m |
| 8 | 0,0503 | 0,503 | 5,03 |
| 10 | 0,0785 | 0,785 | 7,85 |
| 12 | 0,1131 | 1,131 | 11,31 |
| 14 | 0,1539 | 1,539 | 15,39 |
| 16 | 0,2011 | 2,011 | 20,11 |
| 18 | 0,2545 | 2,545 | 25,45 |
| 20 | 0,3142 | 3,142 | 31,42 |
| 22 | 0,3801 | 3,801 | 38,01 |
| 24 | 0,4524 | 4,524 | 45,24 |
| 26 | 0,5309 | 5,309 | 53,09 |
| 28 | 0,6158 | 6,158 | 61,58 |
| 30 | 0,7069 | 7,069 | 70,69 |
| 32 | 0,8042 | 8,042 | 80,42 |
| 34 | 0,9079 | 9,079 | 90,79 |
| 36 | 1,0179 | 10,179 | 101,79 |
| 38 | 1,1341 | 11,341 | 113,41 |
| 40 | 1,2566 | 12,566 | 125,66 |
| 42 | 1,3854 | 13,854 | 138,54 |
| 44 | 1,5205 | 15,205 | 152,05 |
| 46 | 1,6619 | 16,619 | 166,19 |
| 48 | 1,8096 | 18,096 | 180,96 |
| 50 | 1,9635 | 19,635 | 196,35 |
| 52 | 2,1237 | 21,237 | 212,37 |
| 54 | 2,2902 | 22,902 | 229,02 |
| 56 | 2,4630 | 24,630 | 246,30 |
| 100 | 7,8540 | 78,540 | 785,40 |
| 110 | 8,6590 | 86,590 | 856,90 |
Pipes with a diameter of more than 110 mm are rarely used for supplying and discharging water from a private house, so their volume is not indicated. Such pipes are used in urban sewers and for the removal of effluents from an apartment building.In this case, the volume of liquid is calculated taking into account additional parameters, for example, the resistance of pipes made of steel or cast iron.
When calculating the volume of water for a private house, it is recommended to round the values upwards in case you have to install additional water intake points.
