• 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 mmSpeed 1.50 Meters per secondMaximum flow rate in m3/sMaximum flow rate in m3/hMaximum flow rate in l/minMaximum flow rate in l/s
101.500,0001180,42417,0690,118
121.500,0001700,610710,1790,170
141.500,0002310,831313,8540,231
161.500,0003021,085718,0960,302
201.500,0004711,696528,2740,471
261.500,0007962,867047,7840,796
301.500,0010603,817063,6171,060
331.500,0012834,618676,9771,283
381.500,0017016,1242102,0701,701
401.500,0018856,7858113,0971,885
501.500,00294510,6029176,7142,945

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 mmSpeed 2.00 Meters per secondMaximum flow rate in m3/sMaximum flow rate in m3/hMaximum flow rate in l/minMaximum flow rate in l/s
102.000,000157080,56559,42480,157
122.000,000226190,814313,57170,226
142.000,000307881,108418,47250,308
162.000,000402121,447624,12740,402
202.000,000628322,261937,69910,628
262.000,001061863,822763,71141,062
302.000,001413725,089484,82291,414
332.000,001710606,1581102,63571,711
382.000,002268238,1656136,09372,268
40 2.000,002513279,0478150,79632,513
502.000,0039269914,1372235,61933,927

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.