Steel Pipe Schedules and Dimensions

The nominal bore is loosely related to the i/d of the pipe, there are different wall thicknesses or schedules available for each size, the o/d stays constant for each NB.

The heavier the schedule of pipe, the smaller the bore.

Here we have both imperial and metric units.

Imperial

Inches
NB	OD (Inches)	Pipe Schedule
NB	OD (Inches)	SCH 5	SCH 10	SCH 20	SCH 30	SCH 40	SCH 60	SCH 80	SCH 100	SCH 120	SCH 160
3/4	1.05	0.065	0.11	X	0.095	0.113	X	X	0.17	X	0.219
1	1.315	0.065	0.11	X	0.114	0.133	X	X	0.2	X	0.25
1 1/2	1.9	0.065	0.11	X	0.125	0.145	X	X	0.225	X	0.281
2	2.375	0.065	0.12	X	X	0.154	X	X	0.25	X	0.344
2 1/2	2.875	0.083	0.12	X	X	0.203	X	X	0.3	X	0.375
3	3.5	0.083	0.12	X	X	0.216	X	X	0.35	X	0.438
4	4.5	0.083	0.12	X	X	0.237	X	X	0.437	X	0.531
5	5.563	0.109	0.12	X	X	0.258	X	X	0.5	X	0.625
6	6.625	0.109	0.13	X	X	0.28	X	X	0.562	X	0.719
8	8.625	0.109	0.15	0.25	0.277	0.322	0.406	0.5	0.593	0.719	0.906
10	10.75	0.134	0.17	0.25	0.307	0.365	0.5	0.594	0.718	0.843	1.125
12	12.75	0.156	0.18	0.25	0.33	0.406	0.562	0.687	0.843	1.0	1.312
14	14.0	0.156	0.25	0.312	0.375	0.437	0.593	0.75	0.937	1.093	1.406