20 inch Schedule 10S pipe Dimensions

Dimensions

Published dimensions for 20 inch Schedule 10S pipe.
Trade size	NPS 20 · DN 500
Schedule	Schedule 10S
Standard	ASME B36.19M (stainless steel pipe)
Outside diameter	20.000" · 508.00 mm
Wall thickness	0.218" · 5.54 mm
Inside diameter	19.564" · 496.92 mm
Weight, plain end	not published

NPS 20 schedule 10s in numbers

NPS 20 schedule 10s pipe measures 20.000 in (508.00 mm) across the outside with a 0.218 in wall, so the bore is 19.564 in (496.92 mm). That bore gives a flow area of 300.6 in² and holds 15.62 US gallons per foot (193.9 litres per metre). The outside diameter is 91.7 times the wall, and the steel itself has a cross-section of 13.55 in². One trade size up, NPS 22 in the same schedule carries 1.21 times the flow area.

Schedule 5 is the next lighter wall at NPS 20: 0.188 in, 0.030 in thinner, which opens the bore to 19.624 in and adds 0.6% to the flow area.

Schedule 10 is the next heavier wall at NPS 20: 0.250 in, 0.032 in thicker, which narrows the bore to 19.500 in and cuts 0.7% from the flow area.

Next trade size up in this schedule: NPS 22 schedule 10s, bore 21.564 in.

Worked out from the dimensions

Section properties and capacity of 20 inch Schedule 10S pipe, computed from the outside diameter and bore.
Flow area	300.6 in²
Capacity	15.62 US gal/ft · 193.9 L/m
Metal area	13.55 in²
Moment of inertia	662.8 in⁴
Section modulus	66.28 in³
Radius of gyration	6.994 in
Outside surface	5.236 ft² per foot

Plain geometry of a hollow circle with OD = 20.000 in and ID = 19.564 in: flow area π/4·ID², metal area π/4·(OD² − ID²), moment of inertia π/64·(OD⁴ − ID⁴), section modulus I ÷ (OD/2), radius of gyration √(I ÷ metal area), capacity flow area × 12 ÷ 231 (231 in³ to the US gallon). Nominal dimensions, so mill tolerance and corrosion allowance are not included.

Why 20 inch pipe is not 20 inches

Nominal Pipe Size is a label, not a measurement. NPS 20 pipe has an outside diameter of 20.000 inches, and it keeps that outside diameter in every schedule made. What the schedule number changes is the wall: at schedule 10s the wall is 0.218 inches, so the bore comes out at 19.564 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 20

Same outside diameter of 20.000 inches throughout - only the wall and the bore move.

Every other published schedule for NPS 20.
Schedule	Wall (in)	ID (in)	Weight (lb/ft)
Schedule 5 · 5S	0.188	19.624	39.82
Schedule 10	0.250	19.500	52.70
Schedule 40	0.594	18.812	123.23
Schedule 60	0.812	18.376	166.56
Schedule 80	1.031	17.938	209.06
Schedule 100	1.281	17.438	256.34
Schedule 120	1.500	17.000	296.65
Schedule 140	1.750	16.500	341.41
Schedule 160	1.969	16.062	379.53
Standard wall (STD) · 20, 40S	0.375	19.250	78.67
Extra strong (XS) · 30, 80S	0.500	19.000	104.23

Frequently asked questions

What is the wall thickness of 20 inch schedule 10s pipe?

0.218 inches (5.54 mm). The outside diameter is 20.000 inches (508.00 mm) whatever the schedule, so this wall leaves an inside diameter of 19.564 inches.

What is the inside diameter of 20 inch schedule 10s pipe?

19.564 inches (496.92 mm). Inside diameter is outside diameter minus twice the wall: 20.000 - 2 x 0.218 = 19.564 inches.

Is 20 inch pipe actually 20 inches?

No. NPS 20 is a trade size, not a measurement. The pipe measures 20.000 inches across the outside and 19.564 inches across the bore in this schedule. Only the outside diameter is fixed across schedules.

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 B36.19M (stainless 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 2 independent published sources:

Dimensions of steel and stainless steel pipes, ASME B36.10 and ASME B36.19 - Wermac, edition not stated (read 2026-08-27)
Nominal Pipe Size - Wikipedia, revision read 2026-08-27 (read 2026-08-27)

Sources disagree here. Published tables split on the last digit here - 5.54 mm (b3610m-wermac), 5.537 mm (b3610m-wikipedia). The figure printed is 0.218 in (5.54 mm), carried by the majority of the sources. The two readings describe the same wall: they differ by less than a thousandth of an inch, far inside the mill tolerance of minus 12.5 percent on wall thickness.

Last-digit inch walls across the whole table: 0.594, 0.688, 0.719, 0.844, 0.938, 1.094, 1.219, 1.438, 1.969, 2.344 in (b3610m-fbc) against 0.593, 0.687, 0.718, 0.843, 0.937, 1.093, 1.218, 1.437, 1.968, 2.343 in (b3610m-wikipedia). Two families of inch figures are in circulation, one a thousandth of an inch below the other, and they come from rounding the millimetre wall the standard tabulates rather than from any difference in the pipe. The higher family is what the majority of the sources read here carry and is what this site prints; the affected rows say so individually. Nothing turns on the choice: the wall tolerance is minus 12.5 percent, which at a half-inch wall is sixty times the gap.

NPS 14 extra strong (XS): 0.469 in (b3610m-fbc) against 0.500 in (b3610m-etb) against 0.500 in (b3610m-wikipedia). 0.500 in is printed here. Two of the three inch sources give it, both millimetre sources give 12.70 mm which is 0.500 in, and extra strong is a 0.500 in wall at every size from NPS 12 up. The 0.469 in reading looks like a misplaced row in that one chart, but it is recorded rather than deleted.

20 inch Schedule 10S pipe