Schedule 40 and Schedule 80 steel pipe share the same outside diameter at a given nominal pipe size (NPS), but Sch 80 has a thicker wall and a smaller inside diameter. For NPS 2, the nominal walls are 0.154 in (3.91 mm) and 0.218 in (5.54 mm), respectively. Use the charts below to compare dimensions and calculated pipe weight before checking a drawing or specifying a connection.
The tables cover 13 common sizes from NPS 1/2 through NPS 12. Inch values are based on ASME B36.10-2022, with metric equivalents and nominal plain-end steel weights. Additional sections explain STD/XS, stainless steel S-schedules and the limits of comparing steel and PVC schedules.
Pipe Schedule Chart: Schedule 40 and Schedule 80 Dimensions
Select the NPS or corresponding DN, then read across to compare OD, nominal wall thickness and calculated ID. All dimensions in this first table are inches. Sch 40 and Sch 80 refer to steel pipe under ASME B36.10.
| NPS | DN | OD | Sch 40 Wall | Sch 40 ID | Sch 80 Wall | Sch 80 ID |
|---|---|---|---|---|---|---|
| 1/2 | 15 | 0.840 | 0.109 | 0.622 | 0.147 | 0.546 |
| 3/4 | 20 | 1.050 | 0.113 | 0.824 | 0.154 | 0.742 |
| 1 | 25 | 1.315 | 0.133 | 1.049 | 0.179 | 0.957 |
| 1-1/4 | 32 | 1.660 | 0.140 | 1.380 | 0.191 | 1.278 |
| 1-1/2 | 40 | 1.900 | 0.145 | 1.610 | 0.200 | 1.500 |
| 2 | 50 | 2.375 | 0.154 | 2.067 | 0.218 | 1.939 |
| 2-1/2 | 65 | 2.875 | 0.203 | 2.469 | 0.276 | 2.323 |
| 3 | 80 | 3.500 | 0.216 | 3.068 | 0.300 | 2.900 |
| 4 | 100 | 4.500 | 0.237 | 4.026 | 0.337 | 3.826 |
| 6 | 150 | 6.625 | 0.280 | 6.065 | 0.432 | 5.761 |
| 8 | 200 | 8.625 | 0.322 | 7.981 | 0.500 | 7.625 |
| 10 | 250 | 10.750 | 0.365 | 10.020 | 0.594 | 9.562 |
| 12 | 300 | 12.750 | 0.406 | 11.938 | 0.688 | 11.374 |
Source: ASME B36.10-2022, Table 2-1. OD and nominal wall thickness follow the standard. Inside diameters are calculated as OD − 2 × wall thickness and are not guaranteed bore sizes.
Pipe Schedule Chart in Millimeters
This companion chart gives the metric equivalents. Wall thicknesses are rounded to 0.01 mm and calculated IDs to 0.1 mm. Metric OD figures are displayed using the standard rounded values; use consistent unrounded values where a design calculation requires greater precision.
| NPS | DN | OD (mm) | Sch 40 Wall (mm) | Sch 40 ID (mm) | Sch 80 Wall (mm) | Sch 80 ID (mm) |
|---|---|---|---|---|---|---|
| 1/2 | 15 | 21.3 | 2.77 | 15.8 | 3.73 | 13.9 |
| 3/4 | 20 | 26.7 | 2.87 | 20.9 | 3.91 | 18.8 |
| 1 | 25 | 33.4 | 3.38 | 26.6 | 4.55 | 24.3 |
| 1-1/4 | 32 | 42.2 | 3.56 | 35.1 | 4.85 | 32.5 |
| 1-1/2 | 40 | 48.3 | 3.68 | 40.9 | 5.08 | 38.1 |
| 2 | 50 | 60.3 | 3.91 | 52.5 | 5.54 | 49.3 |
| 2-1/2 | 65 | 73.0 | 5.16 | 62.7 | 7.01 | 59.0 |
| 3 | 80 | 88.9 | 5.49 | 77.9 | 7.62 | 73.7 |
| 4 | 100 | 114.3 | 6.02 | 102.3 | 8.56 | 97.2 |
| 6 | 150 | 168.3 | 7.11 | 154.1 | 10.97 | 146.3 |
| 8 | 200 | 219.1 | 8.18 | 202.7 | 12.70 | 193.7 |
| 10 | 250 | 273.1 | 9.27 | 254.5 | 15.09 | 242.9 |
| 12 | 300 | 323.9 | 10.31 | 303.2 | 17.48 | 288.9 |
What Does Sch Mean in Pipe Size?
Sch stands for Schedule, the standardized wall-thickness designation used with nominal pipe size. A pipe marked NPS 2 Sch 40 has a nominal outside diameter of 2.375 in (60.3 mm) and a nominal wall thickness of 0.154 in (3.91 mm).
Three measurements matter when you read a pipe schedule chart.
NPS (Nominal Pipe Size). A dimensionless size designation, not a measured diameter.
OD (Outside Diameter). The external diameter of the pipe. It stays the same across schedules at one NPS.
Wall thickness. The nominal distance between the outer and inner pipe surfaces. It is what the schedule number changes.
The nominal inside diameter (ID) follows from the other two:
ID = OD − 2 × Wall Thickness
A Schedule number identifies a nominal wall-thickness series; it is not a pressure rating. Allowable pressure depends on material properties, design temperature, corrosion allowance, product specification and the governing piping code.
How to Read the Chart
Suppose a drawing calls for NPS 2 Sch 80. Find NPS 2 in the table: the OD is 2.375 in and the Sch 80 wall is 0.218 in. The nominal ID is 2.375 − (2 × 0.218) = 1.939 in. For the same NPS in Sch 40, the nominal ID is 2.067 in. That gap matters when you check internal clearance, hydraulic capacity or the transition to another component.
If you need to identify an existing pipe by measurement, see how to measure pipe size.
Schedule 40 vs Schedule 80: Wall Thickness, Bore and Weight
For NPS 2, the Sch 80 wall is about 41.6% thicker than Sch 40 (0.218 versus 0.154 in). Its nominal internal cross-sectional area is about 12.0% smaller. Neither percentage predicts a corresponding change in flow rate: that requires the fluid properties and the full piping-system conditions.
Schedule 40 vs Schedule 80 Pipe Weight
Sch 80 generally weighs more at the same NPS because more steel surrounds the bore. For carbon steel, ASME B36.10-2022 uses the following nominal plain-end weight formula, where OD and t are in inches and W is in lb/ft:
W = 10.69 × (OD − t) × t
For NPS 2 Sch 40: 10.69 × (2.375 − 0.154) × 0.154 ≈ 3.66 lb/ft. To convert to metric, multiply lb/ft by 1.48816 to get kg/m.
| NPS | Sch 40 (lb/ft) | Sch 40 (kg/m) | Sch 80 (lb/ft) | Sch 80 (kg/m) |
|---|---|---|---|---|
| 1/2 | 0.85 | 1.27 | 1.09 | 1.62 |
| 3/4 | 1.13 | 1.68 | 1.48 | 2.20 |
| 1 | 1.68 | 2.50 | 2.17 | 3.23 |
| 1-1/4 | 2.27 | 3.39 | 3.00 | 4.46 |
| 1-1/2 | 2.72 | 4.05 | 3.63 | 5.41 |
| 2 | 3.66 | 5.44 | 5.03 | 7.48 |
| 2-1/2 | 5.80 | 8.63 | 7.67 | 11.41 |
| 3 | 7.58 | 11.28 | 10.26 | 15.27 |
| 4 | 10.80 | 16.07 | 15.00 | 22.32 |
| 6 | 18.99 | 28.26 | 28.60 | 42.56 |
| 8 | 28.58 | 42.53 | 43.43 | 64.63 |
| 10 | 40.52 | 60.30 | 64.49 | 95.97 |
| 12 | 53.57 | 79.73 | 88.71 | 132.02 |
Nominal calculated carbon-steel plain-end weights, excluding couplings and fittings. Minor differences in the last digit may arise from rounding; actual weight also depends on material density and permitted dimensional variations.
Schedule 40 vs Schedule 80 PVC: Is the Difference the Same?
PVC pipe also uses Schedule 40 and Schedule 80 designations. ASTM D1785 covers specified PVC pressure-pipe materials and schedules, but the steel dimensions above must not be used as PVC design dimensions. A PVC pipe’s pressure rating depends on its material classification, nominal size, temperature and the manufacturer’s rated product. Larger sizes generally have lower ratings within a given PVC pipe series. Threaded or otherwise modified connections can impose additional limitations; always use the appropriate PVC pipe and fitting specifications.
STD, XS, Sch 40 and Sch 80: Are They the Same?
STD means Standard Weight and XS means Extra Strong. They remain common in older drawings and purchasing documents. STD matches Sch 40 through NPS 10, while XS matches Sch 80 through NPS 8. Above these sizes, the designations diverge; XXS and Sch 160 are separate options outside the scope of these charts.
| Designation | Matches | Larger Sizes |
|---|---|---|
| STD | Same nominal wall as Sch 40 through NPS 10 | 0.375 in above NPS 10 |
| XS | Same nominal wall as Sch 80 through NPS 8 | 0.500 in above NPS 8 |
NPS 12 shows the split clearly: Sch 40 has a 0.406 in wall while STD has 0.375 in, and Sch 80 has 0.688 in while XS has 0.500 in. When you replace pipe specified as STD or XS, use the actual designation rather than substituting Sch 40 or Sch 80.
Does Schedule 40S Equal Schedule 40?
Not at every size. ASME B36.19-2022 specifies wrought stainless steel pipe with schedule designations such as 5S, 10S, 40S and 80S. At many NPS values, Sch 40S and 80S match the corresponding steel-pipe wall thicknesses, but the differences shown below matter at larger sizes.
| NPS | Designation | Wall Thickness |
|---|---|---|
| 12 | Sch 40 | 0.406 in |
| 12 | Sch 40S | 0.375 in |
| 12 | Sch 80 | 0.688 in |
| 12 | Sch 80S | 0.500 in |
At NPS 10, 80S is 0.500 in versus 0.594 in for Sch 80. Keep the S suffix and cite the correct dimensional standard when specifying stainless pipe. LILY’s stainless steel unthreaded pipe and pipe fittings category is a relevant starting point for product selection; the applicable product-level dimensions and material grade still need checking.
NPS, DN and Manufacturing Tolerances
NPS and DN are corresponding nominal size designations. They are not direct measurements or exact inch-to-millimeter conversions. NPS 2 corresponds to DN 50 with an OD of 60.3 mm, NPS 4 to DN 100 with 114.3 mm, and NPS 6 to DN 150 with 168.3 mm.
The charts show nominal dimensions. For certain products covered by ASTM A53 or ASTM A106, specified minimum wall thickness may be 12.5% below nominal; do not apply that allowance to every pipe material or specification. Actual tolerances and any purchase-order requirements are governed by the relevant product standard. A calculated nominal ID is therefore not a guaranteed minimum or maximum bore.
How to Specify Pipe and Fittings by Schedule
A clear purchase description identifies the nominal size, schedule, material, manufacturing method and applicable standards. For example: “Pipe, NPS 2, Sch 80, seamless, ASTM A106 Grade B, dimensions per ASME B36.10.” This is a specification example, not a claim about the stock of a particular LILY product.
Then select a connection appropriate to the pipe and system:
Butt-weld connections require compatible wall thickness and end preparation. Browse the iron and steel unthreaded pipe and pipe fittings category for relevant unthreaded product families; check the actual joining style for each product.
Threaded connections need sufficient wall thickness and the specified mating thread form. See the NPT thread chart for thread size and pitch, and confirm the connection specification separately.
Socket-weld and flanged connections use their own dimensional and rating conventions. Fitting class is not simply another name for the pipe schedule or a pressure in psi.
For an overview of common joining methods and fitting types, see our Types of Pipe Fittings guide, which provides additional context for selecting connections and pipe fittings.
LILY also groups pipe fittings by material, connection and duty category. Compare a selected item’s technical details with the drawing; a matching NPS alone does not confirm pressure-temperature suitability.
Frequently Asked Questions
Can Schedule 40 and Schedule 80 steel pipes be connected?
Yes, provided the joint is designed for the two pipe ends and operating conditions. For example, at NPS 2 the nominal wall difference is 0.064 in (0.218 − 0.154 in). A butt-weld joint may need a suitable transition or weld preparation under the applicable piping code.
Can I use a Schedule 80 fitting on Schedule 40 pipe?
It can be appropriate, but the answer depends on the fitting type and joint design. Matching NPS does not make the fitting and pipe interchangeable in every connection. Verify the fitting rating, mating geometry, joining procedure and the pressure-temperature limits of the assembled system.
Technical References
ASME B36.10-2022 — Welded and Seamless Wrought Steel Pipe. Reference for nominal steel pipe dimensions, wall thicknesses and calculated pipe weights.
ASME B36.19-2022 — Welded and Seamless Wrought Stainless Steel Pipe. Reference for stainless steel S-schedule dimensions.
ASTM D1785 — Standard Specification for Poly(Vinyl Chloride) (PVC) Plastic Pipe, Schedules 40, 80, and 120. Reference for the PVC schedule discussion.
Need Help Matching a Pipe or Fitting?
For a product match or quotation, contact LILY Bearing. Include the pipe NPS, schedule, material specification, end connection, operating conditions and any drawing or existing part number.
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