In the process of selecting, installing or purchasing PVC drainage pipes, many people will encounter a common confusion: it is clearly marked with the outer diameter (such as De50, De75), but when it is actually used, it is necessary to know the inner diameter - after all, the inner diameter is directly related to the drainage flow, pipeline suitability, and even affects the later use effect. Today, let's disassemble the conversion logic of the outer diameter and inner diameter of PVC drainage pipes, and attach a quick query table of commonly used specifications to help you figure out the size correspondence at one time.

First of all, two core concepts must be clarified: the outer diameter (De) is the maximum diameter of the outer wall of the pipe, and it is also the most commonly used marking method for PVC drainage pipes (such as "50 pipes" and "110 pipes" often said in decoration, referring to De50 and De110); the inner diameter (dn) is the diameter of the inner wall of the pipe, which directly determines the fluid's ability to pass through. Many people will take it for granted that "inner diameter = outer diameter -2 wall thickness", but there is a key misunderstanding here: the wall thickness of PVC drainage pipes is not a fixed value - it depends on the pressure level of the pipe (such as S1, S2, S4, S5). The lower the grade (such as S5), the thinner the wall thickness, and the higher the grade (such as S1), the thicker the wall thickness and the stronger the pressure bearing capacity.

For example, for pipes that are also De110, the wall thickness of S5 class (lightweight, commonly used for ordinary household drainage) is 3.2mm, and the inner diameter is about 103.6mm; while the wall thickness of S2 class (heavyweight, used for high-pressure drainage) can reach 8.1mm, and the inner diameter is only about 93.8mm - the difference between the inner diameters of the two is nearly 10mm, which directly affects the drainage efficiency. Therefore, it is better to check the specification table hard, which is the most reliable way.

the most commonly used PVC drainage pipe specifications in home improvement and engineering are sorted out below (take GB/T 5836.1-2018 standard S5 level as an example, suitable for ordinary household and commercial water pipe drainage scenes):

- De50 (common in hand basins, balcony floor drains): outer diameter 50mm, wall thickness 2.0mm, inner diameter about 46mm;

- De75 (common in kitchen sinks, shower area drainage): outer diameter 75mm, wall thickness 2.3mm, inner diameter about 70.4mm;

- De110 (common in toilets, main drainage pipes): outer diameter 110mm, wall thickness 3.2mm, inner diameter about 103.6mm;

- De160 (common in floor main drainage, basement drainage): outer diameter 160mm, wall thickness 4.0mm, inner diameter about 152mm;

- De200 (common in large public buildings, residential total Drainage): The outer diameter is 200mm, the wall thickness is 5.0mm, and the inner diameter is about 190mm.

It should be noted that these parameters are the standard values of the conventional S5 class (lightweight). If it is used for special scenarios (such as high pressure drainage, underground buried pipes), a higher pressure level (such as S4 or S2) needs to be selected. At this time, the wall thickness increases, and the inner diameter will decrease accordingly. In addition, products from different manufacturers may have a wall thickness tolerance of 0.3mm. When actually purchasing, be sure to confirm the parameter table provided by the manufacturer to avoid size discrepancies.

In fact, the conversion of the outer diameter and inner diameter of the PVC drain pipe does not require a complicated formula. The key is to "choose the right label + check the specifications": first determine the required outer diameter according to the drainage scene (for example, choose De110 for the toilet drain and De50 for the sink), and then check the corresponding wall thickness according to the pressure requirements of the use scene (S5 for ordinary household use and S4 for high-pressure scenarios), and finally calculate the inner diameter - or a simpler way: directly compare the specification table provided by the manufacturer to obtain the exact value of the outer diameter, wall thickness and inner diameter at one time.

Finally, a reminder: the parameters of different standards (such as GB/T 5836.1-2018) may be slightly different, and the actual application is subject to the test report provided by the manufacturer. Master these logics, you can avoid the error of "hard calculation of inner diameter", and quickly select the right PVC drain pipe.