NPS Pipe Outside Diameter Chart

These outside diameter values apply across the common schedule range (10, 40, 80, and heavier) for each NPS. For wall thickness and calculated bore by schedule, see the Pipe Inside Diameter Chart and Pipe Schedule Chart.

OD affects fittings, clamps, hangers, pipe supports, wall and floor penetrations, sleeves, insulation sizing, grooved couplings, saddles, and flange or component fit. Unlike inside diameter, OD is largely unaffected by schedule within a given NPS dimensional system, since schedule changes are absorbed by wall thickness instead.

ASME B36.10-2022 states that NPS 12 and smaller have outside diameters numerically larger than their nominal size.

For smaller pipe sizes, the nominal size historically related more closely to usable bore than to today’s outside diameter. As wall systems became standardized, OD remained fixed for fitting compatibility while wall thickness varied by schedule, which caused inside diameter to vary as well. The modern result is that NPS identifies a standardized pipe family, not a direct tape-measure diameter.

For bore-specific calculations, see the Pipe Inside Diameter Chart.

No. For a given NPS in the normal ASME steel-pipe system, the standardized OD stays the same while schedule changes wall thickness. For NPS 4, Schedule 40 OD equals 4.500 in and Schedule 80 OD also equals 4.500 in, but the walls and resulting inside diameters differ.

Every column matches for each NPS row. Wall thickness and bore differ between these schedules, but not the value shown here; see the Pipe Wall Thickness Chart for the wall-thickness comparison.

ASME B36.10-2022 covers welded and seamless wrought steel pipe for high or low temperature and pressure service, standardizing NPS/DN designations, outside diameters, nominal wall thicknesses, and the resulting weight relationships. ASME B36.10 is a dimensional standard; it does not by itself define every material grade or service application, since separate material specifications govern those requirements.

Pipe manufactured to material specifications such as ASTM A53 or ASTM A106 typically uses the B36.10 dimensional sizes covered in this chart. This page focuses on outside diameter, not material grade selection; for pipe weight based on these same OD and wall dimensions, see the Steel Pipe Weight Chart.

B36.19 covers welded and seamless wrought stainless steel pipe and matches the familiar B36.10 OD family at these sizes.

ASME B36.19 notes that some 10S, 40S, and 80S stainless wall thicknesses differ from B36.10 values. Those wall differences change the inside diameter, not the fundamental OD size for a given NPS.

ASME states that NPS 12 and smaller have outside diameters numerically larger than their nominal sizes.

In the conventional B36.10 size series, pipe beginning at NPS 14 has an OD numerically matching the NPS designation exactly.

This makes large-pipe sizing more intuitive than the small-NPS series covered in the previous section.

Conversion: 1 in = 25.4 mm.

The tabulated OD is the nominal standardized value. Actual manufactured pipe carries permitted dimensional tolerances depending on the pipe specification, manufacturing process, size, material, and the applicable ASTM, API, or other product standard. Do not treat a chart OD as a guaranteed micrometer reading to unlimited precision; for precision fit applications, check the specific product specification and manufacturer tolerances directly.

ASME distinguishes pipe from tube: pipe uses NPS nominal designations, while tubing is commonly designated by its actual outside diameter. As a result, 1-inch pipe has an OD of 1.315 in, while 1-inch tubing can literally have an OD of 1.000 in, depending on the tubing specification. Confirm which system applies before ordering fittings or matching components.

Tubing systems vary by product and industry, so exceptions to this general pattern exist; always confirm the governing specification for a specific tubing product.

ASTM D1785 is the active standard for PVC Schedule 40, 80, and 120 pressure pipe, describing it as an OD-controlled pipe system. PVC manufacturer catalogs commonly publish sizes that align with the familiar IPS/NPS outside diameter family.

For complete PVC-specific dimensional data including wall thickness and pressure class, see the PVC Pipe Size Chart.

For the same nominal PVC pipe size under ASTM D1785, Schedule 40 and Schedule 80 generally share the same controlled outside diameter. Schedule 80 has a thicker wall and therefore a smaller inside diameter than Schedule 40 at the same nominal size, mirroring the steel pipe relationship covered earlier on this page.

Types K, L, M, DWV, and Medical Gas copper tube are designated by standard nominal sizes, with the actual outside diameter consistently 1/8 in larger than the nominal standard size designation.

For complete copper-specific dimensional data by type, see the Copper Pipe Size Chart.

For the same nominal copper water-tube size, Types K, L, and M use the same outside diameter but different wall thicknesses. This is conceptually similar to steel pipe schedules keeping OD fixed while wall thickness varies, but applied to copper’s own dimensional system.

K/L/M/DWV copper is named by nominal standard size, where actual OD is 1/8 in larger than the label. ACR (air conditioning and refrigeration) tubing, by contrast, is designated by its actual outside diameter directly. This explains why a refrigeration technician and a plumber can use apparently different size terminology for physically related copper tubing products.

HDPE pipe can be manufactured to different OD series. IPS (Iron Pipe Size) HDPE follows the same OD family as steel pipe, while DIPS (Ductile Iron Pipe Size), sometimes called DIOD, follows the larger ductile-iron OD family.

External fit determines compatibility with couplings, grooved fittings, compression systems, clamps, saddles, restraints, and hangers. A fitting sized for 6.625 in OD cannot automatically be assumed to fit 6.900 in OD, even if both products are casually called nominal 6-inch pipe. Always confirm actual OD, not nominal size, before ordering these components.

External coatings such as galvanizing, epoxy, polyethylene coatings, or wraps can increase effective field OD beyond the standard bare-pipe value. For tight sleeves or couplings, verify manufacturer requirements rather than assuming a universal coating allowance. Real pipe can also have allowable ovality, meaning one caliper measurement may differ from another taken on a different axis; measure in multiple directions when precision matters for close-fit couplings or machining, and do not invent a universal ovality tolerance since the applicable product specification governs.