• The speed of the water must be at maximum for a horizontal circulation of 2 meters per second. (For example in the basement in a crawl space in your technical room).
  • The speed in your riser should be a maximum of 1.5 metres per second.

Calculation formula

We will not deal here with the problem of pressure drops in an installation, however it is important to think about the right balance between the number of appliances served and the diameter of their supply.

The maximum flow rate can be calculated by the following formula :

The maximum flow rate in m3 per second is equal to the area of your pipe diameter in m2 multiplied by the silent speed in meters per second.

D (m3/s) = (π d ² (in meters) / 4) x V (meter per second)

For example, for a copper pipe with an internal diameter of 10 mm the maximum flow rate for a speed of 1.5 metres per second is :

(3,14159*0,01*0,01/4) *1,5= 0,0001178 m3/s

In cubic metres per hour : 0.0001178*3600 = 0,4241m3/h

In litres per minute : 0,4241*1000/60= 7,0686 l/mn

We can thus make the following table for the copper tubes that we propose to you:

Inner diameter of the copper pipe in mm Speed 1.50 Meters per second Maximum flow rate in m3/s Maximum flow rate in m3/h Maximum flow rate in l/min Maximum flow rate in l/s
10 1.50 0,000118 0,4241 7,069 0,118
12 1.50 0,000170 0,6107 10,179 0,170
14 1.50 0,000231 0,8313 13,854 0,231
16 1.50 0,000302 1,0857 18,096 0,302
20 1.50 0,000471 1,6965 28,274 0,471
26 1.50 0,000796 2,8670 47,784 0,796
30 1.50 0,001060 3,8170 63,617 1,060
33 1.50 0,001283 4,6186 76,977 1,283
38 1.50 0,001701 6,1242 102,070 1,701
40 1.50 0,001885 6,7858 113,097 1,885
50 1.50 0,002945 10,6029 176,714 2,945

For example, for a copper pipe with an internal diameter of 10 mm the maximum flow rate for a speed of 2 meters per second is :

(3,14159*0,01*0,01/4) *2= 0,00015 m3/s

In cubic metres per hour : 0.00015708*3600 = 0,5655m3/h

In litres per minute : 0,56548*1000/60= 9,42477 l/mn

We can thus make the following table for the copper tubes that we propose to you:

Inner diameter of the copper pipe in mm Speed 2.00 Meters per second Maximum flow rate in m3/s Maximum flow rate in m3/h Maximum flow rate in l/min Maximum flow rate in l/s
10 2.00 0,00015708 0,5655 9,4248 0,157
12 2.00 0,00022619 0,8143 13,5717 0,226
14 2.00 0,00030788 1,1084 18,4725 0,308
16 2.00 0,00040212 1,4476 24,1274 0,402
20 2.00 0,00062832 2,2619 37,6991 0,628
26 2.00 0,00106186 3,8227 63,7114 1,062
30 2.00 0,00141372 5,0894 84,8229 1,414
33 2.00 0,00171060 6,1581 102,6357 1,711
38 2.00 0,00226823 8,1656 136,0937 2,268
40  2.00 0,00251327 9,0478 150,7963 2,513
50 2.00 0,00392699 14,1372 235,6193 3,927

We hope that thanks to this information, this popularization of simple formula that you will be able to better understand the basic principles of your installation of your sanitary network.