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

PVC Schedule 40 and 80 dimensions, sharing steel-pipe outside diameters
NPS	OD (in)	Sch 40 wall	Sch 40 ID	Sch 80 wall	Sch 80 ID
1/2	0.840	0.109	0.6220	0.147	0.5460
3/4	1.050	0.113	0.8240	0.154	0.7420
1	1.315	0.133	1.0490	0.179	0.9570
1-1/4	1.660	0.140	1.3800	0.191	1.2780
1-1/2	1.900	0.145	1.6100	0.200	1.5000
2	2.375	0.154	2.0670	0.218	1.9390
2-1/2	2.875	0.203	2.4690	0.276	2.3230
3	3.500	0.216	3.0680	0.300	2.9000
4	4.500	0.237	4.0260	0.337	3.8260
6	6.625	0.280	6.0650	0.432	5.7610
8	8.625	0.322	7.9810	0.500	7.6250

Take the table with you — CSV · JSON

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