Learn how to read PN, SDR, Schedule and Class pipe pressure ratings, convert kgf/cm² to bar, de-rate for temperature, and pick the right pipe class.
Quick answer
Work out the maximum pressure your system can ever see (tank height, or pump shut-off pressure, plus a margin for surges and hot water), then buy the next rating above that number.
Last updated: 26 July 2026 · By Puranmal Sons & Ceramix Syndicate, wholesale building-material distributor, Indore · Prices are indicative for mid-2026.
A pipe's pressure rating is like the weight limit painted on a bridge. A bridge rated for 10 tonnes will not collapse the moment an 11-tonne truck crosses, but keep overloading it and one day it fails. Pipes are the same: the rating tells you how hard the water inside can push, day after day for decades, without the pipe splitting.
What makes water push hard? Mostly height. Water at the bottom of a tall tank pushes harder than water at the bottom of a short one — every metre of height adds roughly one-tenth of a bar of pressure. So a roof tank three floors up pushes gently, a ten-storey riser pushes three times harder, and a borewell pump can push harder than any building's tank.
The confusing part is that different pipe families print the rating in different codes: PN 10, Class 4, SDR 11, Schedule 40, 6 kgf/cm². They are all answering the same question — "how thick is the wall compared to the pipe's width?" — just in different languages. Thicker wall for the same diameter means higher pressure capacity, more plastic, and a higher price.
One-sentence verdict: work out the maximum pressure your system can ever see (tank height, or pump shut-off pressure, plus a margin for surges and hot water), then buy the next rating above that number.
| Situation | Typical maximum pressure | Minimum rating to buy |
|---|---|---|
| Ground-floor tap fed by roof tank, 1–4 storey house (10–15 m head) | ~1.0–1.5 bar | uPVC Class 2 (4 kgf/cm²) technically passes; buy Class 3 (6 kgf/cm²) / PN 6 for joint strength and handling |
| Down take riser in a 10-storey building (~32 m head + surge) | ~3.2 bar static, more with hammer | PN 6 minimum; PN 8–10 on the lowest floors |
| Hot water line from solar heater or geyser (60–80°C) | Low pressure, high temperature | CPVC SDR 11 (IS 15778 Class 1) or PPR PN 20 — never plain PVC |
| Domestic pump discharge (1 HP, shut-off head 40–50 m) | ~4–5 bar at shut-off | PN 6–8 / uPVC 6–8 kgf/cm² |
| Borewell delivery main, 60 m head pump | ~6 bar at duty, 7+ bar at shut-off | PN 10 / uPVC 10 kgf/cm² / HDPE PE100 SDR 17 or thicker |
| Farm sprinkler main (3–3.5 bar at nozzle + friction + surge) | ~4.5–5.5 bar | PN 6 laterals, PN 8 mains (HDPE or uPVC) |
| Gravity drainage / vent lines | Near zero | Non-pressure SWR pipe — pressure class irrelevant |
PN stands for "Pressure Nominal" — the pressure in bar the pipe is designed to carry continuously with water at the reference temperature. European standards use 20°C; Indian standards such as IS 4985 (uPVC) and IS 15778 (CPVC) rate pipes at 27°C, which suits Indian ambient conditions.
Older Indian practice, and most trade counters, still quote uPVC in kgf/cm² ("kg pressure"). The units are nearly interchangeable:
| Unit | In bar | In psi | In metres of water |
|---|---|---|---|
| 1 bar | 1.00 | 14.5 | 10.2 |
| 1 kgf/cm² | 0.98 | 14.2 | 10.0 |
| 1 MPa | 10.0 | 145 | 102 |
| 1 psi | 0.069 | 1.00 | 0.70 |
So "6 kgf/cm² pipe", "PN 6" and "0.6 MPa" describe essentially the same duty. IS 4985 groups uPVC pipes into classes:
| IS 4985 class | Working pressure at 27°C | Approx. bar |
|---|---|---|
| Class 1 | 2.5 kgf/cm² | 2.5 |
| Class 2 | 4 kgf/cm² | 4 |
| Class 3 | 6 kgf/cm² | 6 |
| Class 4 | 8 kgf/cm² | 8 |
| Class 5 | 10 kgf/cm² | 10 |
| Class 6 | 12.5 kgf/cm² (2000 edition); the 2021 revision extends the top class to 15 | 12.5–15 |
SDR (Standard Dimension Ratio) is simply outside diameter divided by wall thickness: SDR = OD / t. A 110 mm pipe with a 10 mm wall is SDR 11. Lower SDR = thicker wall = higher pressure capacity. SDR is honest in a way PN is not: it describes the pipe itself, while the pressure that geometry can carry depends on the material's strength.
For polyethylene, the link between geometry, material and rating is:
PN (bar) = 20 × MRS / (C × (SDR − 1))
where MRS is the Minimum Required Strength (8 MPa for PE 80, 10 MPa for PE 100, per IS 4984:2016) and C is the overall service (design) coefficient, minimum 1.25 for water. Check it: PE 100, SDR 11 → 20 × 10 / (1.25 × 10) = 16 bar (PN 16). PE 100, SDR 17 → 20 × 10 / (1.25 × 16) = 10 bar (PN 10). This is why the same SDR 11 pipe is PN 16 in PE 100 but only PN 12.5 in PE 80 — same wall, weaker material.
All of the above comes from hoop stress — the stress trying to split the pipe lengthwise. In thin-wall form:
P = 2 × S × t / (D − t)
where P is pressure, S is allowable design stress, t is wall thickness, D is outside diameter.
Worked example — 110 mm PE 100 pipe, SDR 11 (t = 10 mm). Design stress S = MRS / C = 10 / 1.25 = 8 MPa.
P = 2 × 8 × 10 / (110 − 10) = 160 / 100 = 1.6 MPa = 16 bar.
That matches the PN 16 label exactly — the printed rating is not arbitrary; it is this calculation with a 25% safety factor already inside.
Schedule pipe (ASTM D1785 for PVC, ASTM F441 for CPVC) fixes the wall thickness per size, not the pressure. Because the wall does not grow proportionally with diameter, the pressure rating falls as the pipe gets bigger. Published ratings for PVC Schedule 80 at 23°C illustrate this: ½" = 850 psi (~59 bar), ¾" = 690 psi, 1" = 630 psi, 2" = 400 psi (~28 bar). A metric PN 10 pipe, by contrast, is 10 bar whether it is 25 mm or 250 mm, because the wall scales with diameter (constant SDR). Practical consequence: "Schedule 40 is strong pipe" is meaningless without stating the size, and comparing Schedule to PN requires converting the specific size's psi rating.
Ratings hold only at the reference temperature. Above it, plastic creeps faster and the usable pressure drops. Multiply the printed rating by a de-rating factor:
| Water temperature | PVC (per Spears Sch 80 data) | CPVC (per Prince Pipes IS 15778 manual, generic) | HDPE (Engineering ToolBox) |
|---|---|---|---|
| 27°C | 1.00 (Indian rating basis) | 1.00 | ~0.9–1.0 |
| 38–40°C | 0.62 | 0.82 | 0.8 |
| 49–50°C | 0.40 | 0.65 | 0.7 |
| 60°C | 0.22 (absolute limit) | 0.50 | 0.4 (practical limit) |
| 71°C | not permitted | 0.40 | not permitted |
| 82°C | not permitted | 0.25 | not permitted |
PPR uses a different system — PN classes at 20°C per DIN 8077 with 50-year pressure–temperature curves — which is why hot-water PPR is almost always specified as PN 20 even though the line pressure is low. Factors vary slightly between manufacturers; always check the datasheet for the brand you are buying. The headline lesson: a "15 kg" PVC pipe carrying 60°C water is really a 3.3 kg pipe.
Static pressure from height: P (bar) = height (m) × 0.098. Add the pump's contribution using its shut-off head (pressure at zero flow — the highest it can ever produce), not the duty-point head on the nameplate. Then allow for water hammer: when a valve slams or a pump stops, a surge wave (Joukowsky: ΔP = ρ × a × Δv) can add several bar for a fraction of a second. Fast-closing quarter-turn taps and long pump mains are the usual culprits; a margin of 25–50% over calculated maximum pressure, or the next class up, is cheap insurance. After installation, the accepted field convention (e.g., AWWA C605 for PVC mains) is to hydrotest at 1.5 × maximum working pressure at the lowest point of the section — another reason not to buy exactly at your working pressure.
Finally, read the printed line before you buy. An IS 4985 pipe must carry, at minimum: maker's name (e.g., Prince, Astral as market examples), the standard (IS 4985), size × wall or class designation (e.g., 110 × 4.2 or PN 6 / Class 3), batch/date code, and the ISI certification mark. IS 4984 HDPE potable-water pipe is blue, or black with blue longitudinal stripes, marked with grade (PE 80/PE 100), PN and SDR. No marking line means no traceable rating — walk away.
Example 1 — Four-storey Indore house, roof tank supply. Tank bottom sits 13.5 m above the ground-floor kitchen tap. Static pressure = 13.5 × 0.098 = 1.32 bar. Even with a pressure-boosting pump adding 1.5 bar, the maximum is under 3 bar. uPVC Class 2 (4 kgf/cm²) passes numerically, but Class 3 (6 kgf/cm²) is the sensible buy: thicker walls take solvent-cement joints and site handling better, and quick-closing mixer taps cause hammer spikes. Extra cost is small at ½"–1" sizes.
Example 2 — Borewell delivery main, 60 m head pump. Duty pressure at the pump outlet ≈ 60 × 0.098 = 5.9 bar. The pump curve shows shut-off head of 74 m → 74 × 0.098 = 7.3 bar, which the pipe sees every time the outlet valve is closed with the pump running. Add surge on start/stop across a 300 m main. Selection: minimum PN 10 — uPVC 10 kgf/cm² (IS 4985 Class 5) or HDPE PE 100 SDR 17 (PN 10); if starts are frequent and unsoftened, PE 100 SDR 13.6 (PN 12.5) buys fatigue margin. A PN 6 pipe here would sit permanently above its rating and fail early.
Example 3 — Solar hot-water return at 60°C in CPVC. CPVC SDR 11 is rated 28.14 kgf/cm² at 27°C (IS 15778 data, Prince Pipes manual). At 60°C apply the 0.50 factor: 28.14 × 0.50 = 14.1 kgf/cm² ≈ 13.8 bar usable. A rooftop solar loop runs under 1 bar, so SDR 11 has a 14× margin even hot. But if the same duty peaks at 82°C (stagnation), the factor is 0.25 → 7.0 kgf/cm² — still fine here, but a thin SDR 13.5 line (22.22 × 0.25 = 5.6 kgf/cm²) is getting close to real limits in pumped hot-recirculation systems. This is why hot lines default to SDR 11.
Indicative, mid-2026, may vary. Basis: a published manufacturer list price (Sudhakar, April 2025 list) for 90 mm (3") uPVC self-socket pipe, IS 4985, per 6 m length; converted to per-metre. Wholesale net rates in Indore after trade discounts are substantially lower, but the ratios between classes hold roughly constant across brands.
| IS 4985 class (90 mm uPVC) | Indicative list price per 6 m | Approx. per metre | Step-up vs previous class |
|---|---|---|---|
| 2.5 kgf/cm² (Class 1) | ₹1,363 | ~₹227 | — |
| 4 kgf/cm² (Class 2) | ₹1,918 | ~₹320 | +41% |
| 6 kgf/cm² (Class 3) | ₹2,760 | ~₹460 | +44% |
The economics of getting it wrong are asymmetric. Over-speccing one class (say 4 → 6 kgf/cm² on a 100 m farm main) costs roughly 40–45% more on the pipe — a few thousand rupees. Under-speccing costs a burst: the replacement pipe, plus excavation or wall-breaking, labour, water damage and downtime, which routinely exceeds the original pipe cost several times over. When the calculated pressure sits near a class boundary, buy the class above; when it sits far below, do not pay for two classes of headroom you will never use.
Ignoring temperature de-rating on hot lines. A PVC pipe marked 10 kgf/cm² keeps only about 22% of that at 60°C and is not permitted above it, so geyser and solar lines in PVC fail at pressures that look "safe" on the label. Use CPVC (SDR 11) or PPR PN 20 for anything above 45°C.
Sizing to the pump's duty head instead of shut-off head. The nameplate head is at design flow; close a valve and the pressure climbs to shut-off head, often 20–30% higher. Read the pump curve and rate the pipe for shut-off plus a surge margin.
Treating "Schedule 40" as one fixed pressure. Schedule ratings fall steeply with size — Schedule 80 PVC is about 59 bar at ½" but only 28 bar at 2". Always check the rating for the specific diameter, or specify in PN/class where the rating is size-independent.
Confusing units. 6 kgf/cm² ≈ 6 bar ≈ 87 psi — but 6 psi is only 0.4 bar. Mixing up psi and kgf/cm² on imported fittings or pump gauges leads to wildly wrong selections; convert everything to bar before comparing.
Buying by weight or "feel" instead of the marking line. Unmarked pipe may be made from recycled or filler-heavy compound with no guaranteed strength regardless of wall thickness. Insist on the ISI mark, the standard number and the class printed along the pipe.
Skipping surge allowance on long pumped mains. Water hammer from pump trips or fast valves adds a transient spike on top of static pressure; a main selected exactly at working pressure fails at joints first. Keep 25–50% margin or fit slow-closing valves and non-return arrangements.
Practically yes. 1 kgf/cm² = 0.98 bar, so a 10 kgf/cm² pipe is rated ~9.8 bar versus PN 10's 10 bar. For selection purposes treat them as equivalent; the 2% difference is far smaller than your safety margin should be.
A roof tank on a 1–4 storey house produces under 1.5 bar at the lowest tap, so even Class 2 (4 kgf/cm²) passes on paper. Most plumbers in Indore fit 6 kgf/cm² (Class 3) or CPVC/ASTM lines for better joint integrity and hammer resistance — a reasonable default.
No. PVC's usable pressure drops to roughly a fifth of its rating by 60°C and it is unsuitable beyond that, while geysers deliver 55–65°C and solar systems can stagnate above 80°C. Use CPVC per IS 15778 (SDR 11 for hot lines) or PPR PN 20.
The outside diameter is 11 times the wall thickness. Per IS 15778, CPVC SDR 11 (Class 1) is rated about 28 kgf/cm² at 27°C and about 7 kgf/cm² at 82°C; SDR 13.5 (Class 2) is thinner and rated about 22 and 5.6 kgf/cm² respectively.
Multiply the height difference in metres by 0.098 to get bar. A tank 10 m above a tap gives ~0.98 bar; 30 m (about ten storeys) gives ~2.9 bar. Width and volume of the tank do not matter — only height.
It is always stronger, never "better value" automatically. Each class step costs roughly 40% more material for capacity you may never use, and thicker walls slightly reduce bore. Match the class to calculated maximum pressure plus margin.
Field convention for water lines is 1.5 × the maximum working pressure, held long enough to inspect all joints (AWWA C605 uses 1.5× at the lowest point of the tested section). The test pressure must not exceed the pipe's rated class.
Puranmal Sons & Ceramix Syndicate is a wholesale supplier of plumbing pipes, tiles and sanitaryware in Indore, stocking uPVC, CPVC and HDPE ranges from manufacturers including Prince Pipes and Astral. If you are unsure which pressure class suits your building, borewell or farm project, share your tank height, pump details or drawings — the team will help you match the class and quantity, with delivery across Indore, Dewas, Ujjain, Pithampur, Dhar and Mhow. Call 95222-20983 or visit us at 254, Jawahar Marg, Rajmohalla, Indore for current rates.
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