Steel NB Pipe Dimensions

NB (Nominal Bore) pipe sizing is a reference number that loosely tracks a pipe's internal bore, but — like DN — shouldn't be read as an exact bore measurement, since the actual internal diameter varies with wall thickness/schedule even within the same NB size. This chart gives outside diameter, wall thickness, and bore dimensions for standard steel NB pipe sizes in both inches and millimetres.

For matching flange dimensions at a given size, see our Flange Dimensions pages (indexed by the equivalent DN size); for stainless steel pipe, see our Stainless Steel NB Pipe chart.

Dimensional Chart for Nominal Bore Pipe in both Inches and millimetres.

Dimensions shown are in mm, if you wish to convert to Inches, please use our universal converter.

If you are interested in different sections why not try these?

NOMINAL BORE PIPE DIMENSIONS

Nominal Pipe Size Inches	Nominal Pipe Size mm	OD Inches	OD mm	Schedule Designations ANSI/ASME	Wall Thickness Inches	Wall Thickness mm	Lbs/Ft	Kg/M
1/8	6	0.405	10.3	10/10S	0.049	1.24	0.1863	0.28
1/8	6	0.405	10.3	STD/40/40S	0.068	1.73	0.2447	0.36
1/8	6	0.405	10.3	XS/80/80S	0.095	2.41	0.3145	0.47
1/4	8	0.54	13.7	10/10S	0.065	1.65	0.3297	0.49
1/4	8	0.54	13.7	STD/40/40S	0.088	2.24	0.4248	0.63
1/4	8	0.54	13.7	XS/80/80S	0.119	3.02	0.5351	0.8
3/8	10	0.675	17.1	10/10S	0.065	1.65	0.4235	0.63
3/8	10	0.675	17.1	STD 40/40S	0.091	2.31	0.5676	0.84
3/8	10	0.675	17.1	XS 80/80S	0.126	3.2	0.7388	1.1
1/2	15	0.84	21.3	5/5S	0.065	1.65	0.5383	0.8
1/2	15	0.84	21.3	10/10S	0.083	2.11	0.671	1
1/2	15	0.84	21.3	STD 40/40S	0.109	2.77	0.851	1.27
1/2	15	0.84	21.3	XS 80/80S	0.147	3.73	1.088	1.62
1/2	15	0.84	21.3	160	0.188	4.78	1.309	1.95
1/2	15	0.84	21.3	XX	0.294	7.47	1.714	2.55
3/4	20	1.05	26.7	5/5S	0.065	1.65	0.6838	1.02
3/4	20	1.05	26.7	10/10S	0.083	2.11	0.8572	1.28
3/4	20	1.05	26.7	STD/40/40S	0.113	2.87	1.131	1.68
3/4	20	1.05	26.7	XS/80/80S	0.154	3.91	1.474	2.19
3/4	20	1.05	26.7	160	0.219	5.56	1.944	2.89
3/4	20	1.05	26.7	XX	0.308	7.82	2.441	3.63
1	25	1.315	33.4	5/5S	0.065	1.65	0.8678	1.29
1	25	1.315	33.4	10/10S	0.109	2.77	1.404	2.09
1	25	1.315	33.4	STD/40/40S	0.133	3.38	1.679	2.5
1	25	1.315	33.4	XS/80/80S	0.179	4.55	2.172	3.23
1	25	1.315	33.4	160	0.25	6.35	2.844	4.23
1	25	1.315	33.4	XX	0.358	9.09	3.659	5.45
1 1/4	32	1.66	42.2	5/5S	0.065	1.65	1.107	1.65
1 1/4	32	1.66	42.2	10/10S	0.109	2.77	1.806	2.69
1 1/4	32	1.66	42.2	STD/40/40S	0.14	3.56	2.273	3.38
1 1/4	32	1.66	42.2	XS/80/80S	0.191	4.85	2.997	4.46
1 1/4	32	1.66	42.2	160	0.25	6.35	3.765	5.6
1 1/4	32	1.66	42.2	XX	0.382	9.7	5.214	7.76
1 1/2	40	1.9	48.3	5/5S	0.065	1.65	1.274	1.9
1 1/2	40	1.9	48.3	10/10S	0.109	2.77	2.085	3.1
1 1/2	40	1.9	48.3	STD/40/40S	0.145	3.68	2.718	4.05
1 1/2	40	1.9	48.3	XS/80/80S	0.2	5.08	3.631	5.4
1 1/2	40	1.9	48.3	160	0.281	7.14	4.859	7.23
1 1/2	40	1.9	48.3	XX	0.4	10.16	6.408	9.54
2	50	2.375	60.3	5/5S	0.065	1.65	1.604	2.39
2	50	2.375	60.3	10/10S	0.109	2.77	2.638	3.93
2	50	2.375	60.3	STD/40/40S	0.154	3.91	3.653	5.44
2	50	2.375	60.3	XS/80/80S	0.218	5.54	5.022	7.47
2	50	2.375	60.3	160	0.344	8.74	7.462	11.11
2	50	2.375	60.3	XX	0.436	11.07	9.029	13.44
2 1/2	65	2.875	73	5/5S	0.083	2.11	2.475	3.68
2 1/2	65	2.875	73	10/10S	0.12	3.05	3.531	5.26
2 1/2	65	2.875	73	STD/40/40S	0.203	5.16	5.793	8.62
2 1/2	65	2.875	73	XS/80/80S	0.276	7.01	7.661	11.4
2 1/2	65	2.875	73	160	0.375	9.53	10.01	14.9
2 1/2	65	2.875	73	XX	0.552	14.02	13.69	20.37
3	80	3.5	88.9	5/5S	0.083	2.11	3.029	4.51
3	80	3.5	88.9	10/10S	0.12	3.05	4.332	6.45
3	80	3.5	88.9	STD/40/40S	0.216	5.49	7.576	11.27
3	80	3.5	88.9	XS/80/80S	0.3	7.62	10.25	15.25
3	80	3.5	88.9	160	0.438	11.13	14.32	21.31
3	80	3.5	88.9	XX	0.6	15.24	18.58	27.65
3 1/2	90	4	101.6	5/5S	0.083	2.11	3.472	5.17
3 1/2	90	4	101.6	10/10S	0.12	3.05	4.973	7.4
3 1/2	90	4	101.6	STD 40/40S	0.226	5.74	9.109	13.56
3 1/2	90	4	101.6	XS 80/80S	0.318	8.08	12.5	18.6
3 1/2	90	4	101.6	XX	0.636	16.15	22.85	34.01
4	100	4.5	114.3	5/5S	0.083	2.11	3.915	5.83
4	100	4.5	114.3	10/10S	0.12	3.05	5.613	8.35
4	100	4.5	114.3	STD 40/40S	0.237	6.02	10.79	16.06
4	100	4.5	114.3	XS 80/80S	0.337	8.56	14.98	22.29
4	100	4.5	114.3	120	0.438	11.13	19	28.28
4	100	4.5	114.3	160	0.531	13.49	22.51	33.5
4	100	4.5	114.3	XX	0.674	17.12	27.54	40.99
5	125	5.563	141.3	5/5S	0.109	2.77	6.349	9.45
5	125	5.563	141.3	10/10S	0.134	3.4	7.77	11.56
5	125	5.563	141.3	STD 40/40S	0.258	6.55	14.62	21.76
5	125	5.563	141.3	XS 80/80S	0.375	9.53	20.78	30.93
5	125	5.563	141.3	120	0.5	12.7	27.04	40.24
5	125	5.563	141.3	160	0.625	15.88	32.96	49.05
5	125	5.563	141.3	XX	0.75	19.05	38.55	57.37
6	150	6.625	168.3	5/5S	0.109	2.77	7.585	11.29
6	150	6.625	168.3	10/10S	0.134	3.4	9.289	13.82
6	150	6.625	168.3	120	0.562	14.27	36.39	54.16
6	150	6.625	168.3	160	0.719	18.26	45.35	67.49
8	200	8.625	219.1	10/10S	0.148	3.76	13.6	19.94
8	200	8.625	219.1	20	0.25	6.35	22.36	33.28
8	200	8.625	219.1	30	0.277	7.04	24.7	36.76
8	200	8.625	219.1	STD/40/40S	0.322	8.18	28.55	42.49
8	200	8.625	219.1	60	0.406	10.31	35.64	53.04
8	200	8.625	219.1	XS/80/80S	0.5	12.7	43.39	64.58
8	200	8.625	219.1	100	0.594	15.09	50.95	75.83
8	200	8.625	219.1	120	0.719	18.26	60.71	90.35
8	200	8.625	219.1	140	0.812	20.62	67.76	100.84
8	200	8.625	219.1	XX	0.875	22.23	72.42	107.78

FREQUENTLY ASKED QUESTIONS

Is NB the same as DN?

They're closely related and often used interchangeably in casual conversation — NB (Nominal Bore) is the traditional imperial-derived reference, while DN (Nominal Diameter) is the metric/ISO equivalent. For a given nominal size, the two typically correspond, but always check the specific standard being referenced for exact dimensions rather than assuming an automatic match.

Why doesn't the actual bore match the NB size exactly?

NB is a nominal reference, not a precise bore measurement — the actual internal diameter depends on wall thickness (schedule), which varies with pressure rating even at the same nominal size. Always check the dimensional chart for the actual bore rather than assuming NB equals bore.

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