← AskMachinist · Guides · Calculator · 🔎 Search

Pipe Schedule Chart: OD and Wall Thickness

Guide · Updated October 28, 2026

Nominal pipe size (NPS) is a name, not a measurement. From 1/8 through 12 in, the outside diameter of a given NPS is fixed and is larger than the name, so 1 in pipe is really 1.315 in OD. The schedule number sets the wall thickness, so a heavier schedule keeps the same OD and makes the bore smaller. From NPS 14 up, the OD equals the nominal size. The values below are from ASME B36.10M for welded and seamless steel pipe; stainless pipe to B36.19M shares the ODs and, for these sizes, the 40S and 80S walls match Schedule 40 and 80.

Need an exact reference size?

Build any gage block stack with the free Gage Block Calculator. Free, no login.

Step by step

Measure the OD: Mic or caliper the outside of the pipe away from any weld bead or threads.
Find the NPS: Match the OD to the chart; the OD identifies the size regardless of schedule.
Measure the wall: Use a tube micrometer or ball mic on an end, or an ultrasonic thickness gage in the middle of a run.
Identify the schedule: Compare the wall with the Schedule 40 and 80 columns.
Calculate the ID: ID = OD − 2 × wall.
Check weight if needed: lb/ft = 10.69 × (OD − wall) × wall for carbon steel.

Schedule 40 and 80 chart (ASME B36.10M)

NPS 1/8: OD 0.405, Sch 40 wall 0.068, Sch 80 wall 0.095
1/4: OD 0.540, 0.088, 0.119
3/8: OD 0.675, 0.091, 0.126
1/2: OD 0.840, 0.109, 0.147
3/4: OD 1.050, 0.113, 0.154
1: OD 1.315, 0.133, 0.179
1-1/4: OD 1.660, 0.140, 0.191
1-1/2: OD 1.900, 0.145, 0.200
2: OD 2.375, 0.154, 0.218
2-1/2: OD 2.875, 0.203, 0.276
3: OD 3.500, 0.216, 0.300
3-1/2: OD 4.000, 0.226, 0.318
4: OD 4.500, 0.237, 0.337
5: OD 5.563, 0.258, 0.375
6: OD 6.625, 0.280, 0.432
8: OD 8.625, 0.322, 0.500
10: OD 10.750, 0.365, 0.500 (XS)
12: OD 12.750, 0.406, 0.500 (XS)

All dimensions are in inches. Standard (STD) weight equals Schedule 40 through NPS 10, and Extra Strong (XS) equals Schedule 80 through NPS 8. At 10 and 12 in they split: Schedule 80 is 0.594 and 0.688 in wall while XS stays at 0.500 in.

Heavier walls

Schedule 160 walls for small sizes are 1/2 in: 0.188, 3/4: 0.219, 1: 0.250, 1-1/2: 0.281, 2: 0.344 in. Double extra strong (XXS) is about twice the XS wall: 1/2 in XXS is 0.294 and 2 in XXS is 0.436 in. Heavy wall pipe is handy stock for bushings and spacers because the bore is already close to size.

Formulas

ID = OD − 2t
Steel weight, lb/ft = 10.69 × (OD − t) × t (OD and t in inches)
Metal area = π × (OD − t) × t
Flow area = π × ID² ÷ 4

The 10.69 constant comes from steel density of 0.2836 lb/in³ times 12 in times π. For aluminum pipe multiply the steel weight by about 0.35, and for stainless by about 1.02.

Worked example: 2 in Schedule 40

OD 2.375, wall 0.154. ID = 2.375 − 0.308 = 2.067 in, which matches the B36.10M table. Weight = 10.69 × (2.375 − 0.154) × 0.154 = 10.69 × 2.221 × 0.154 = 3.66 lb/ft, matching the published 3.65 lb/ft.

In Schedule 80, ID = 2.375 − 0.436 = 1.939 in and weight = 10.69 × 2.157 × 0.218 = 5.03 lb/ft.

Worked example: making a bushing from 1 in Schedule 80

OD 1.315, wall 0.179, so ID = 0.957 in. To finish a bushing at 1.250 OD × 1.000 ID you need to turn 0.0325 in per side off the outside and bore 0.0215 in per side out of the inside, leaving 0.125 in wall. Mill-run pipe walls can vary by −12.5% from nominal under the pipe specs, so check the actual wall before relying on it and indicate the bore, since pipe is not always concentric.

Pipe size versus tube size

Pipe is called out by NPS and schedule. Tubing is called out by actual OD and wall, such as 1.000 OD × 0.065 wall. A 1 in pipe fitting will not fit 1 in OD tube. Hydraulic tubing uses tube OD and dash numbers, which are a separate system.

Common problems

Treating NPS as the OD, assuming wall from schedule without measuring (mill tolerance is often −12.5% on wall), confusing Schedule 80 with XS at 10 in and up, and measuring the wall at a pipe end that has been chamfered or reamed. Check walls with a tube mic or ultrasonic gage.

FAQ

What is the OD of 1 inch pipe?

1.315 in for every schedule.

What is the wall of 2 inch Schedule 40 pipe?

0.154 in, giving a 2.067 in ID.

Is Schedule 40 the same as standard wall?

Yes through NPS 10 in carbon steel per ASME B36.10M.

How do I check a tube micrometer?

Check the gage itself before trusting a measurement: gage blocks set mics, calipers and indicators; build any stack free at gageblockcalc.com.

Related guides and calculators

Build your stack in seconds

The free Gage Block Calculator finds the fewest-block combination for inch and metric sets, with wear blocks. No login.

Questions? Ask a machinist.

General shop information only — follow your drawing, tool maker's data and your quality system.