Piping

Pipe Size Chart (NPS)

Nominal pipe size is a label, not a measurement. This table gives the dimensions that actually matter — outside diameter, wall, bore and flow area.

Below 14″, NPS does not equal any real dimension: 2″ pipe has a 2.375″ OD and a 2.067″ bore in Sch 40. Going from Schedule 40 to 80 shrinks the bore about 7.4% but cuts flow area about 14.1% — the area penalty is roughly double the diameter penalty.

Nominal pipe size to outside diameter, wall thickness, inside diameter and flow area by schedule

1/8	Sch 10	0.405	0.049	0.3070	0.0740	0.187
1/8	Sch 40	0.405	0.068	0.2690	0.0568	0.245
1/8	Sch 80	0.405	0.095	0.2150	0.0363	0.315
1/4	Sch 10	0.540	0.065	0.4100	0.1320	0.330
1/4	Sch 40	0.540	0.088	0.3640	0.1041	0.425
1/4	Sch 80	0.540	0.119	0.3020	0.0716	0.536
3/8	Sch 10	0.675	0.065	0.5450	0.2333	0.424
3/8	Sch 40	0.675	0.091	0.4930	0.1909	0.568
3/8	Sch 80	0.675	0.126	0.4230	0.1405	0.740
1/2	Sch 10	0.840	0.083	0.6740	0.3568	0.672
1/2	Sch 40	0.840	0.109	0.6220	0.3039	0.852
1/2	Sch 80	0.840	0.147	0.5460	0.2341	1.089
1/2	Sch 160	0.840	0.188	0.4640	0.1691	1.311
3/4	Sch 10	1.050	0.083	0.8840	0.6138	0.858
3/4	Sch 40	1.050	0.113	0.8240	0.5333	1.132
3/4	Sch 80	1.050	0.154	0.7420	0.4324	1.475
3/4	Sch 160	1.050	0.219	0.6120	0.2942	1.946
1	Sch 10	1.315	0.109	1.0970	0.9452	1.405
1	Sch 40	1.315	0.133	1.0490	0.8643	1.681
1	Sch 80	1.315	0.179	0.9570	0.7193	2.174
1	Sch 160	1.315	0.250	0.8150	0.5217	2.847
1-1/4	Sch 10	1.660	0.109	1.4420	1.6331	1.807
1-1/4	Sch 40	1.660	0.140	1.3800	1.4957	2.275
1-1/4	Sch 80	1.660	0.191	1.2780	1.2828	3.000
1-1/4	Sch 160	1.660	0.250	1.1600	1.0568	3.769
1-1/2	Sch 10	1.900	0.109	1.6820	2.2220	2.087
1-1/2	Sch 40	1.900	0.145	1.6100	2.0358	2.721
1-1/2	Sch 80	1.900	0.200	1.5000	1.7671	3.635
1-1/2	Sch 160	1.900	0.281	1.3380	1.4061	4.864
2	Sch 10	2.375	0.109	2.1570	3.6542	2.641
2	Sch 40	2.375	0.154	2.0670	3.3556	3.657
2	Sch 80	2.375	0.218	1.9390	2.9529	5.027
2	Sch 160	2.375	0.344	1.6870	2.2352	7.470
2-1/2	Sch 10	2.875	0.120	2.6350	5.4532	3.535
2-1/2	Sch 40	2.875	0.203	2.4690	4.7878	5.799
2-1/2	Sch 80	2.875	0.276	2.3230	4.2383	7.669
2-1/2	Sch 160	2.875	0.375	2.1250	3.5466	10.023
3	Sch 10	3.500	0.120	3.2600	8.3469	4.336
3	Sch 40	3.500	0.216	3.0680	7.3927	7.584
3	Sch 80	3.500	0.300	2.9000	6.6052	10.264
3	Sch 160	3.500	0.438	2.6240	5.4078	14.339
3-1/2	Sch 10	4.000	0.120	3.7600	11.1036	4.978
3-1/2	Sch 40	4.000	0.226	3.5480	9.8868	9.119
3-1/2	Sch 80	4.000	0.318	3.3640	8.8880	12.518
4	Sch 10	4.500	0.120	4.2600	14.2531	5.619
4	Sch 40	4.500	0.237	4.0260	12.7303	10.802
4	Sch 80	4.500	0.337	3.8260	11.4969	14.999
4	Sch 160	4.500	0.531	3.4380	9.2833	22.533
5	Sch 10	5.563	0.134	5.2950	22.0202	7.778
5	Sch 40	5.563	0.258	5.0470	20.0058	14.633
5	Sch 80	5.563	0.375	4.8130	18.1937	20.800
5	Sch 160	5.563	0.625	4.3130	14.6100	32.997
6	Sch 10	6.625	0.134	6.3570	31.7391	9.299
6	Sch 40	6.625	0.280	6.0650	28.8903	18.994
6	Sch 80	6.625	0.432	5.7610	26.0667	28.604
6	Sch 160	6.625	0.719	5.1870	21.1311	45.400
8	Sch 10	8.625	0.148	8.3290	54.4848	13.413
8	Sch 40	8.625	0.322	7.9810	50.0270	28.584
8	Sch 80	8.625	0.500	7.6250	45.6635	43.434
8	Sch 160	8.625	0.906	6.8130	36.4558	74.770
10	Sch 10	10.750	0.165	10.4200	85.2757	18.673
10	Sch 40	10.750	0.365	10.0200	78.8543	40.526
10	Sch 80	10.750	0.594	9.5620	71.8104	64.498
10	Sch 160	10.750	1.125	8.5000	56.7450	115.769
12	Sch 10	12.750	0.180	12.3900	120.5681	24.191
12	Sch 40	12.750	0.406	11.9380	111.9317	53.582
12	Sch 80	12.750	0.688	11.3740	101.6053	88.725
12	Sch 160	12.750	1.312	10.1260	80.5315	160.443
14	Sch 10	14.000	0.250	13.5000	143.1388	36.752
14	Sch 40	14.000	0.438	13.1240	135.2765	63.509
14	Sch 80	14.000	0.750	12.5000	122.7185	106.246
16	Sch 10	16.000	0.250	15.5000	188.6919	42.098
16	Sch 40	16.000	0.500	15.0000	176.7146	82.859
16	Sch 80	16.000	0.844	14.3120	160.8757	136.762
18	Sch 10	18.000	0.250	17.5000	240.5282	47.443
18	Sch 40	18.000	0.562	16.8760	223.6809	104.778
18	Sch 80	18.000	0.938	16.1240	204.1905	171.108
20	Sch 10	20.000	0.250	19.5000	298.6477	52.789
20	Sch 40	20.000	0.594	18.8120	277.9456	123.242
20	Sch 80	20.000	1.031	17.9380	252.7190	209.093
24	Sch 10	24.000	0.250	23.5000	433.7361	63.481
24	Sch 40	24.000	0.688	22.6240	402.0024	171.477
24	Sch 80	24.000	1.219	21.5620	365.1472	296.902

23 nominal sizes across Schedule 10 / 40 / 80 / 160 · 83 rows

Why OD stays fixed and the bore moves

For a given NPS, outside diameter is constant across every schedule — that is what lets the same fittings and threads work regardless of wall thickness. Heavier schedules add material inward, so the bore shrinks while the pipe still fits the same coupling.

The area mistake

Flow capacity goes with cross-sectional area, which scales as the square of diameter. A schedule change that looks like a 7.4% diameter reduction is a 14.1% capacity reduction. Quoting the diameter figure as though it were the flow figure is the most common error in schedule comparisons.

PVC uses the same outside diameters

PVC Schedule 40 and 80 share steel-pipe ODs by design (ASTM D1785), which is why metal and plastic fittings of the same nominal size interchange. Pressure ratings do not transfer — those depend on material and temperature.

Data source and method

Dimensions: ASME B36.10M outside diameters and wall thicknesses; ASTM D1785 for PVC.
Calculation: ID = OD − 2 × wall; flow area = π(ID/2)²; weight = metal cross-section × 12 in × 0.2836 lb/in³.
Verification: Sch 40 bore checked against five published values (NPS 1/2, 1, 2, 4, 6). All exact.

Related charts

Thread size chart — thread geometry, including the pitch conventions NPT builds on
Sheet metal gauge chart — wall thickness in the other unit system fabricators work in