12 inch Extra strong pipe

Dimensions

Published dimensions for 12 inch Extra strong pipe.
Trade size	NPS 12 · DN 300
Schedule	Extra strong (XS)
Standard	ASME B36.10M (welded and seamless wrought steel pipe)
Outside diameter	12.750" · 323.85 mm · designated 323.8 mm in the metric column
Wall thickness	0.500" · 12.70 mm
Inside diameter	11.750" · 298.45 mm
Weight, plain end	65.48 lb/ft · 97.44 kg/m

Cross-check: the standard plain-end weight formula W = 10.6802 x t x (OD - t) gives 65.42 lb/ft here, 0.1% from the published 65.48 lb/ft. The published figure is the one printed above.

Why 12 inch pipe is not 12 inches

Nominal Pipe Size is a label, not a measurement. NPS 12 pipe has an outside diameter of 12.750 inches, and it keeps that outside diameter in every schedule made. What the schedule number changes is the wall: at extra strong (xs) the wall is 0.500 inches, so the bore comes out at 11.750 inches.

That is the practical consequence. Fittings, flanges, supports and threading dies are sized to the outside diameter, so they fit any schedule of the same trade size. Flow, pressure drop and anything that has to pass through the pipe depend on the inside diameter, which changes with every schedule. Order by trade size and schedule; work your hydraulics from the bore.

Other schedules in NPS 12

Same outside diameter of 12.750 inches throughout - only the wall and the bore move.

Every other published schedule for NPS 12.
Schedule	Wall (in)	ID (in)	Weight (lb/ft)
Schedule 5	0.156	12.438	21
Schedule 10	0.180	12.390	24.19
Schedule 20	0.250	12.250	33.41
Schedule 30	0.330	12.090	43.81
Schedule 40	0.406	11.938	53.57
Schedule 60	0.562	11.626	73.22
Schedule 80	0.688	11.374	88.71
Schedule 100	0.844	11.062	107.42
Schedule 120	1.000	10.750	125.61
Schedule 140	1.125	10.500	139.81
Schedule 160	1.312	10.126	160.42
Standard wall (STD)	0.375	12.000	49.61
Double extra strong (XXS)	1.000	10.750	125.61
Schedule 5S	0.156	12.438	not published
Schedule 10S	0.180	12.390	not published
Schedule 40S	0.375	12.000	not published
Schedule 80S	0.500	11.750	not published

Frequently asked questions

What is the wall thickness of 12 inch extra strong (xs) pipe?

0.500 inches (12.70 mm). The outside diameter is 12.750 inches (323.85 mm) whatever the schedule, so this wall leaves an inside diameter of 11.750 inches.

What is the inside diameter of 12 inch extra strong (xs) pipe?

11.750 inches (298.45 mm). Inside diameter is outside diameter minus twice the wall: 12.750 - 2 x 0.500 = 11.750 inches.

Is 12 inch pipe actually 12 inches?

No. NPS 12 is a trade size, not a measurement. The pipe measures 12.750 inches across the outside and 11.750 inches across the bore in this schedule. Only the outside diameter is fixed across schedules.

How much does 12 inch extra strong (xs) pipe weigh?

65.48 pounds per foot plain end (97.44 kg per metre), for carbon steel. Stainless of the same dimensions runs a little lighter, and the figure excludes coatings, linings and fittings.

Where this table stops

This table runs from NPS 1/8 to NPS 24 and stops there. ASME B36.10M itself continues to NPS 80; those larger sizes are not carried here, so a size above NPS 24 is missing rather than undefined.

Where these figures come from

Dimensions are as defined by ASME B36.10M (welded and seamless wrought steel pipe). This site is an independent reference and is not affiliated with, endorsed by or approved by any standards body.

Every value on this page was cross-checked against 5 independent published sources:

ASME B36.10M pipe schedule chart - wall thickness and weights - Flange Bolt Chart, states ASME B36.10M-2018, Table 2.1 (read 2026-08-27)
ASME/ANSI B36.10/19 - carbon, alloy and stainless steel pipe dimensions - Engineering ToolBox, edition not stated (read 2026-08-27)
Dimensions of steel and stainless steel pipes, ASME B36.10 and ASME B36.19 - Wermac, edition not stated (read 2026-08-27)
ANSI / ASME B36.10M pipe dimensions chart - Ferrobend, edition not stated (read 2026-08-27)
Nominal Pipe Size - Wikipedia, revision read 2026-08-27 (read 2026-08-27)