{"id":3578,"date":"2026-10-26T12:10:08","date_gmt":"2026-10-26T04:10:08","guid":{"rendered":"http:\/\/www.rentayamotos.com\/blog\/?p=3578"},"modified":"2026-10-26T12:10:08","modified_gmt":"2026-10-26T04:10:08","slug":"what-is-the-inner-diameter-of-ppr-pipes-4650-0caabd","status":"publish","type":"post","link":"http:\/\/www.rentayamotos.com\/blog\/2026\/10\/26\/what-is-the-inner-diameter-of-ppr-pipes-4650-0caabd\/","title":{"rendered":"What is the inner diameter of PPR pipes?"},"content":{"rendered":"

If you\u2019ve ever walked through a residential construction site, or watched a plumber thread pipes under a sink, you\u2019ve probably heard the term \u201cPPR pipe\u201d thrown around. Polypropylene Random Copolymer (PPR) pipes are the workhorses of modern plumbing, valued for their durability, corrosion resistance, and ease of installation. But when it comes to installing or specifying these pipes, one question comes up again and again for both homeowners and contractors alike: what exactly is the inner diameter of PPR pipes? As a PPR pipe supplier with over a decade in the industry, I\u2019ve spent countless hours walking customers through this detail\u2014and I\u2019m here to break it down clearly, no confusing jargon required. PPR Pipe<\/a><\/p>\n

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First, let\u2019s get one thing straight: inner diameter (often shortened to ID) isn\u2019t the same as outer diameter (OD) \u2014 and that distinction is huge when it comes to PPR pipes. The outer diameter is the measurement of the pipe\u2019s widest point, from one outer wall to the other. That\u2019s the number you\u2019ll see stamped on most standard pipe, like 20mm, 25mm, or 32mm. But the inner diameter is the gap between the two inner walls, which directly impacts flow rate, pressure handling, and how well a pipe works for hot or cold water. Why does this matter? If you pick a pipe based only on outer diameter, you might get a pipe that\u2019s too narrow for your needs, leading to low water pressure, frequent clogs, or even pipe damage over time.<\/p>\n

So how do we calculate the inner diameter of a PPR pipe? It\u2019s simple geometry: take the outer diameter, subtract twice the wall thickness of the pipe. PPR pipes have standardized wall thicknesses set by international plumbing bodies, and those thicknesses depend on the pipe\u2019s pressure rating. Most PPR pipes sold for residential use come in three pressure classes: PN20, PN25, and PN10 (PN stands for \u201cPressure Nominal,\u201d which refers to the maximum pressure the pipe can safely handle at 20\u00b0C, or 68\u00b0F). For example, a 20mm outer diameter PPR pipe: a PN20 version has a wall thickness of 3.4mm, so its inner diameter is 20mm minus (2 x 3.4mm) = 13.2mm. A PN10 20mm pipe has a thinner wall, just 2.0mm, so its inner diameter jumps to 16mm. That\u2019s a big difference, and it\u2019s why matching pressure class to your project is non-negotiable.<\/p>\n

Let\u2019s break down the most common PPR pipe sizes you\u2019ll encounter, along with their inner diameters, to make this concrete. For 20mm OD PPR pipes (the go-to for branch lines in residential plumbing, like taps or shower connections):<\/p>\n