HDPE Pipe Sizes, SDR & PN Chart (DN20–DN1600): How to Choose

Reading an HDPE pipe size is not like reading a metal one, and the mistake costs money. HDPE pipe sizes are set by two numbers working together: DN, the outer diameter in millimeters, and SDR, the ratio of that diameter to the wall thickness. SDR — not a simple "PN wall" — is what sets the pressure rating. Pick the wrong SDR and you either pay for wall you don't need or bury a main that bursts under surge. This guide gives you the full DN20–DN1600 range, the SDR-to-pressure chart, and how to choose without guessing.

The one relationship to hold onto: a lower SDR means a thicker wall and a higher pressure rating; a higher SDR means a thinner wall and a lower rating. Everything else — coils versus lengths, PE100 versus PE80, how surge changes the choice — follows from that.

DN, SDR and Wall: How an HDPE Size Is Defined

Two numbers describe every HDPE pipe. DN (diameter nominal) is the outer diameter in millimeters — a DN110 pipe is 110 mm across the outside, regardless of wall. SDR (Standard Dimension Ratio) is that outer diameter divided by the wall thickness. So a DN110 pipe with an 10 mm wall has an SDR of 11 (110 ÷ 10). Because SDR is a ratio, the same SDR gives the same relative wall — and the same pressure rating — across every diameter, which is why HDPE is classed by SDR rather than by a fixed wall number.

This is the part that trips up buyers coming from metal or even PVC, where a size usually implies one wall. With HDPE it doesn't: two DN110 pipes can have completely different walls and pressure ratings depending on their SDR, and they'll sit side by side on a shelf looking almost identical until you measure the wall or read the print. A DN110 SDR17 is a thinner-walled 10-bar pipe; a DN110 SDR11 is a thicker-walled 16-bar pipe. Same outside diameter, same fittings OD, very different duty. Always specify both the DN and the SDR — a diameter alone tells you nothing about the pressure it will hold.

SDR to Pressure Chart (PE100)

For PE100 (MRS 10 MPa) carrying water, the common SDR classes map to pressure as below. The exact bar figure comes from the ISO formula, but these are the working numbers you'll quote.

Note the grade interaction: those bar figures are for PE100. The same SDR on older PE80 (MRS 8) rates roughly 20% lower — an SDR11 PE80 is about PN12.5, not PN16. If a quote lists an SDR and a pressure that don't match this table, check the grade before you check anything else; the mismatch usually means PE80 sold as PE100, covered in the PE100 vs PE80 comparison.

PN vs SDR: Two Ways to Say the Same Thing

Buyers often see both "PN" and "SDR" on HDPE and assume they're separate specs to pick. They're not — they're two ways of describing the same wall. SDR describes the geometry (diameter-to-wall ratio); PN describes the resulting pressure class in bar at 20°C. For a given grade they move together: on PE100, SDR11 is PN16, SDR17 is PN10. You specify one and the other follows.

The catch is that the PN only holds for a stated grade and temperature. The same SDR at a lower grade (PE80) gives a lower PN, and pressure capacity drops as the water gets warmer — which is why HDPE is a cold-and-ambient material and PN figures are quoted at 20°C. When you order, name the grade, the SDR, and the PN together; if a supplier gives you an SDR and a PN that don't line up on the chart above, that's the flag to stop and check the grade.

The Pressure Formula, In Plain Terms

You don't need to calculate on site, but understanding the formula stops you being fooled. Per ISO 4427 and ISO 12162, the allowable pressure is P = (20 × MRS) ÷ [C × (SDR − 1)], in bar. MRS is the minimum required strength of the resin (10 for PE100, 8 for PE80). C is the design coefficient — a safety factor, at least 1.25 for water. Two things fall out of it: higher-grade resin (bigger MRS) means more pressure at the same SDR, and a lower SDR (thicker wall) means more pressure. The design coefficient is why a pipe rated "16 bar" isn't run at 16 bar continuously — the safety margin is already built in.

One more factor the chart doesn't show: temperature. The PN figures are quoted at 20°C, and HDPE loses pressure capacity as the fluid warms — at higher service temperatures a pipe must be de-rated below its nominal PN. For buried water in the ground this rarely bites, since soil stays cool, but for above-ground runs in hot climates or warm process fluids it matters. If your line runs warm, factor a de-rating allowance into the SDR choice rather than reading the 20°C figure straight off the table.

Diameter Range and How It Ships

HDPE spans a huge range — DN20 to DN1600 — and how a size is supplied changes your install and shipping as much as the diameter itself.

Coils up to DN90 are the big labor saver: a 100 m coil is one continuous pipe with no joints across a trench. But they're also heavier to handle as diameter grows, and they hold a curve memory that needs straightening on lay. Straight lengths above DN110 are easy to fuse but volume-heavy to ship — a 40ft container of large-diameter pipe fills on cubic space long before weight, so confirm loading quantities before you order. The container and coil detail for import is in the importing HDPE guide.

Metric (DN) vs Imperial (IPS) Sizing

One trap on cross-border orders: HDPE is sold in two dimension systems that don't interchange. The metric ISO system uses DN in millimeters (DN20, DN110, DN160) and is standard across Africa, the Middle East, Europe and Asia. The North American IPS (Iron Pipe Size) system uses inch-based ODs that are different numbers — a "4-inch" IPS pipe is not the same OD as DN110. Because fusion and fittings depend on an exact OD match, you cannot mix a metric pipe with an imperial fitting, or vice versa.

For most export markets you want the metric DN/ISO 4427 system end to end — pipe and fittings both metric. State the system explicitly on the order ("metric DN, ISO 4427") so there's no chance of an IPS batch arriving that won't fuse to your metric fittings. If a project inherited imperial infrastructure, transition is done with a flange or a dedicated transition coupler, not by forcing a size that's "close."

How to Choose the Right Size and SDR

Sizing HDPE is a two-step decision: diameter for flow, SDR for pressure. Get them in that order.

Diameter for flow

Pick the diameter from the flow and the acceptable velocity, sizing the mains first and branching down — the same logic as any network. Remember the bore, not the DN, carries the water: a lower SDR (thicker wall) at a given DN has a smaller bore, so on a high-pressure line you sometimes step up a diameter to recover flow lost to the thicker wall.

SDR for pressure — with surge margin

Match the SDR to the working pressure from the chart, then add margin for surge. The pressure spike when a pump starts or a valve slams shut can briefly far exceed the steady pressure, and repeated surge fatigues a wall sized only for static duty. On pumped mains it's standard to choose one SDR step thicker than the steady pressure alone suggests — SDR11 where the math says SDR17 would just cover it. That headroom is cheap next to excavating a fatigued main.

Don't chase the thinnest SDR

A thinner-wall (higher SDR) pipe quotes cheaper because it uses less resin, and that's exactly why an unscrupulous supplier will offer an SDR17 where the spec called for SDR11. Fix the SDR in writing and confirm the wall thickness against it — a pipe that's light for its diameter has a shaved wall, whatever the label says.

A Worked Example

Say you're specifying a village water distribution main pumped at a steady 9 bar. Reading the chart, PE100 SDR17 (PN10) "covers" 9 bar on paper. But it's a pumped line, so surge matters: you step one class thicker to SDR11 (PN16), giving comfortable margin for pump-start and valve-close transients. For diameter, the flow demand points to roughly DN110; because SDR11 has a thicker wall and slightly smaller bore than SDR17, you confirm DN110 still meets velocity, and it does. So the spec is PE100, DN110, SDR11, ordered in 12 m lengths and butt-fused on site.

Now the service connections off that main run at house pressure and short lengths — those take PE100 DN25 SDR11 in coils, electrofused or compression-fitted to the main. One project, two size-and-SDR decisions, each driven by flow first and pressure-with-margin second. That's the whole method.

Common HDPE Sizing Mistakes

• Ordering a DN without an SDR — the diameter alone doesn't set pressure, so the supplier picks the cheapest (thinnest) wall.
• Reading a PE80 pressure off a PE100 chart — same SDR, lower grade, ~20% less pressure. Always tie SDR to grade.
• Sizing to steady pressure on a pumped line — no surge margin, fatigue failure later. Step down one SDR.
• Forgetting bore shrinks with a thicker wall — a low-SDR pipe at the same DN carries less; check velocity, step up a diameter if needed.
• Not matching fitting OD/SDR to the pipe — electrofusion couplers must match the pipe OD exactly to fuse.

Reading the Pipe Marking

Every compliant HDPE pipe prints its own specification down the side: manufacturer, material grade (PE100), diameter, SDR or pressure class, the standard (ISO 4427, EN 12201), a batch or date code, and usually meter marks. That printed line is your first size check — confirm the DN and SDR match your order before anything goes in the trench. Faint or missing marking is a red flag, because reputable factories print clearly for traceability. Match the marking to the fittings too: the fitting must be the same grade and suit the pipe OD and SDR, a point covered in the HDPE fittings guide.

Where Sizing Fits in the Bigger Picture

Size and SDR are one piece of the HDPE decision. The grade sets what each SDR is worth, the joint method depends on diameter (butt fusion for DN90+, electrofusion for smaller), and the fittings have to match both. For the full path from material to sourcing, start with the complete HDPE pipe guide, and for how the diameter drives the jointing choice, see butt fusion vs electrofusion. If you're weighing HDPE against other materials for the job, the HDPE vs PVC vs PPR comparison covers where each wins. Nail the DN and SDR first, though, and the rest of the specification falls into place around them.

Frequently Asked Questions