NPS is nominal
For most sizes, NPS is not the measured outside diameter. Use the standard OD.
Technical guide
Stainless Steel Pipe Size Chart
Pipe size is defined by NPS and schedule: NPS is a designation, outside diameter follows the dimensional standard, and wall thickness changes with schedule.
Dimension standardASME B36.19
Size formatNPS + schedule
Do not confusePipe NPS with tube actual OD
Decision summary
Identify pipe, standard and schedule together
A request for “two-inch stainless” is incomplete until the buyer states pipe versus tube, product specification, NPS, schedule and grade.
Schedule controls wall
A higher schedule generally indicates a thicker nominal wall for the same NPS, subject to the dimensional table.
Product standard controls material
ASME B36.19 supplies dimensions; ASTM A312/A312M or another product standard supplies manufacturing and test requirements.
Pipe is not tube
Tube is commonly ordered by actual OD and wall; do not substitute a tube size chart for an NPS schedule table.
Pressure design is separate
The chart does not determine allowable pressure. Use the governing design code, material properties, temperature and allowances.
Tolerance still applies
Nominal OD and wall are not inspection limits; use the dimensional and product-standard tolerances.
Reference table
Selected stainless pipe dimensions
Nominal dimensions below are selected planning values from the ASME B36.19 size system. Confirm the purchased standard edition and supplier availability.
| NPS | Outside diameter (in) | Schedule 5S wall (in) | Schedule 10S wall (in) | Schedule 40S wall (in) | Schedule 80S wall (in) |
|---|---|---|---|---|---|
| 1/2 | 0.840 | 0.065 | 0.083 | 0.109 | 0.147 |
| 3/4 | 1.050 | 0.065 | 0.083 | 0.113 | 0.154 |
| 1 | 1.315 | 0.065 | 0.109 | 0.133 | 0.179 |
| 1 1/4 | 1.660 | 0.065 | 0.109 | 0.140 | 0.191 |
| 1 1/2 | 1.900 | 0.065 | 0.109 | 0.145 | 0.200 |
| 2 | 2.375 | 0.065 | 0.109 | 0.154 | 0.218 |
| 3 | 3.500 | 0.083 | 0.120 | 0.216 | 0.300 |
| 4 | 4.500 | 0.083 | 0.120 | 0.237 | 0.337 |
| 6 | 6.625 | 0.109 | 0.134 | 0.280 | 0.432 |
| 8 | 8.625 | 0.109 | 0.148 | 0.322 | 0.500 |
Values are nominal inches and are not a complete reproduction of ASME B36.19. Schedule availability and permitted tolerances must be confirmed against the licensed standard and product specification.
Need a pipe size suppliers can verify?
Send NPS, schedule, grade, product standard, manufacturing route, length, ends, tests and destination.
Working method
Write the pipe requirement in a consistent order
A complete line item allows dimensional, material, test and commercial review without guessing what “stainless pipe” means.
State the product specification
Name ASTM A312/A312M, A790/A790M or the governing standard and required edition.
State grade, NPS and schedule
Use the specified TP/UNS grade, nominal pipe size and schedule from the dimensional standard.
Add manufacturing and end details
Specify seamless/welded route where required, length, end preparation, bevel, threading or flange interface.
Define tests and documents
Include hydrostatic or NDE option, PMI, heat treatment, surface, MTC, marking, inspection and packaging.
Limits and escalation
The pipe chart is not a pressure rating
Design code required
Pressure and temperature design requires the governing code, allowable stress, joint factor and corrosion allowance.
Schedule is not universal
Schedule values and availability depend on the dimensional and product standards; do not infer one material system from another.
Fittings must match
Check bore, schedule, rating, end preparation and material standard for fittings, flanges and valves.
Corrosion selection remains separate
Grade selection depends on medium, concentration, temperature, velocity, crevices, cleaning and fabrication.
Visual process context
Show the geometry and inspection context behind the pipe callout.
Reserve one image for the supplied pipe form and another for dimensional or inspection evidence.
Interactive planning aid
Look up OD, wall and nominal ID
Choose an NPS and stainless schedule from the selected table values. Calculated ID equals OD minus twice the nominal wall.
Frequently asked questions
Stainless steel pipe size FAQ
Usually no. NPS is a dimensionless nominal designation; use ASME B36.19 for the standardized outside diameter and schedule wall.
The dimensional system and applicable material/product standard must be checked. For stainless pipe, ASME B36.19 schedules with the S suffix are the primary reference.
For planning, subtract twice the nominal wall thickness from the nominal outside diameter. Actual ID varies with OD and wall tolerances.
No. Tube is commonly specified by actual outside diameter and wall thickness, while pipe uses NPS and schedule designations.
Method, sources and review
Traceable sources and review status
Official standard covering dimensions of welded and seamless wrought stainless steel pipe.
Official product specification for seamless, welded and heavily cold-worked austenitic stainless pipe.
Official general requirements used by multiple alloy and stainless pipe specifications.
Official definition that one international inch equals exactly 25.4 millimetres.
Use the licensed current dimensional and product standards for procurement and inspection. The selected rows and calculator are nominal planning aids, not pressure ratings or tolerance tables.
Pipe dimensions context
Read nominal size, schedule and pressure basis together.
A pipe size chart needs the governing standard, nominal size, schedule, actual wall, end preparation and service basis before it supports a purchase decision.
- Nominal size
- Wall schedule
- Service basis