Threaded Pipe (NPT)

Threaded Pipe (NPT) Dimensions

Look up American National Standard taper pipe thread data for threaded pipe and fittings — threads per inch, pitch, hand-tight engagement and tap drill sizes.

Quick Thread Lookup

ASME B1.20.1

Interactive geometry reference for American National Standard taper pipe threads (NPT).

ASME B1.20.1 NPT Taper (1:16)

Hover over dimension cards or diagram markers to highlight key engagement planes.

Nominal Pipe Size (NPS)OD: 2.3750 in

Pipe OD (D)Outer Dia

2.3750 in

Pitch E₀: 2.2690 in

Threads / inTPI

11.5 threads/in

Pitch P: 0.08696 in

Hand-tight (L₁)5.01 turns

0.4360 in

Pitch E₁: 2.2963 in

Effective (L₂)8.70 turns

0.7565 in

Pitch E₂: 2.3163 in

Wrench Make-up (L₃)Internal

0.2609 in

3.00 threads beyond L₁

Tap Drill Minor (K₀)Tap Info

2.1995 in

Small-end minor diameter

Dimensions Unit

NPT thread dimensions (ASME B1.20.1)

Complete Table 2 geometry · scroll horizontally to view all 24 published columns

Showing 24 of 24 sizes

ASME B1.20.1 NPT taper pipe thread dimensions
Basic geometry					Hand-tight engagement			Effective external thread			Wrench make-up					External thread completion					Thread form
NPS	D (in)	TPI, n	P (in)	E₀ (in)	L₁ (in)	L₁ threads	E₁ (in)	L₂ (in)	L₂ threads	E₂ (in)	L₂−L₁ (in)	L₂−L₁ threads	L₃ (in)	L₃ threads	E₃ (in)	V (in)	V threads	L₄ (in)	L₅ (in)	E₅ (in)	h (in)	ΔØ/turn (in)	K₀ (in)
1/16"	0.3125	27	0.03703704	0.27118	0.1600	4.32	0.28118	0.2611	7.05	0.28750	0.1011	2.73	0.1111	3.00	0.26424	0.1285	3.47	0.3896	0.1870	0.28287	0.02963	0.00231	0.2415
1/8"	0.4050	27	0.03703704	0.36351	0.1615	4.36	0.37360	0.2639	7.13	0.38000	0.1024	2.76	0.1111	3.00	0.35656	0.1285	3.47	0.3924	0.1898	0.37537	0.02963	0.00231	0.3338
1/4"	0.5400	18	0.05555556	0.47739	0.2278	4.10	0.49163	0.4018	7.23	0.50250	0.1740	3.13	0.1667	3.00	0.46697	0.1928	3.47	0.5946	0.2907	0.49556	0.04444	0.00347	0.4329
3/8"	0.6750	18	0.05555556	0.61201	0.2400	4.32	0.62701	0.4078	7.34	0.63750	0.1678	3.02	0.1667	3.00	0.60160	0.1928	3.47	0.6006	0.2967	0.63056	0.04444	0.00347	0.5675
1/2"	0.8400	14	0.07142857	0.75843	0.3200	4.48	0.77843	0.5337	7.47	0.79178	0.2137	2.99	0.2143	3.00	0.74504	0.2479	3.47	0.7815	0.3909	0.78286	0.05714	0.00446	0.7014
3/4"	1.0500	14	0.07142857	0.96768	0.3390	4.75	0.98887	0.5457	7.64	1.00178	0.2067	2.89	0.2143	3.00	0.95429	0.2479	3.47	0.7935	0.4029	0.99286	0.05714	0.00446	0.9106
1"	1.3150	11.5	0.08695652	1.21363	0.4000	4.60	1.23863	0.6828	7.85	1.25631	0.2828	3.25	0.2609	3.00	1.19733	0.3017	3.47	0.9845	0.5089	1.24544	0.06957	0.00543	1.1441
1-1/4"	1.6600	11.5	0.08695652	1.55713	0.4200	4.83	1.58338	0.7068	8.13	1.60131	0.2868	3.30	0.2609	3.00	1.54083	0.3017	3.47	1.0085	0.5329	1.59044	0.06957	0.00543	1.4876
1-1/2"	1.9000	11.5	0.08695652	1.79609	0.4200	4.83	1.82234	0.7235	8.32	1.84131	0.3035	3.49	0.2609	3.00	1.77978	0.3017	3.47	1.0252	0.5496	1.83044	0.06957	0.00543	1.7266
2"	2.3750	11.5	0.08695652	2.26902	0.4360	5.01	2.29627	0.7565	8.70	2.31630	0.3205	3.69	0.2609	3.00	2.25272	0.3017	3.47	1.0582	0.5826	2.30543	0.06957	0.00543	2.1995
2-1/2"	2.8750	8	0.12500000	2.71953	0.6820	5.46	2.76216	1.1375	9.10	2.79063	0.4555	3.64	0.2500	2.00	2.70391	0.4338	3.47	1.5712	0.8875	2.77500	0.10000	0.00781	2.6195
3"	3.5000	8	0.12500000	3.34063	0.7660	6.13	3.38850	1.2000	9.60	3.41563	0.4340	3.47	0.2500	2.00	3.32500	0.4338	3.47	1.6337	0.9500	3.40000	0.10000	0.00781	3.2406
3-1/2"	4.0000	8	0.12500000	3.83750	0.8210	6.57	3.88881	1.2500	10.00	3.91563	0.4290	3.43	0.2500	2.00	3.82188	0.4338	3.47	1.6837	1.0000	3.90000	0.10000	0.00781	3.7374
4"	4.5000	8	0.12500000	4.33438	0.8440	6.75	4.38713	1.3000	10.40	4.41563	0.4560	3.65	0.2500	2.00	4.31875	0.4338	3.47	1.7337	1.0500	4.40000	0.10000	0.00781	4.2343
5"	5.5630	8	0.12500000	5.39073	0.9370	7.50	5.44929	1.4063	11.25	5.47863	0.4693	3.75	0.2500	2.00	5.37511	0.4338	3.47	1.8400	1.1563	5.46300	0.10000	0.00781	5.2907
6"	6.6250	8	0.12500000	6.44609	0.9580	7.66	6.50597	1.5125	12.10	6.54063	0.5545	4.44	0.2500	2.00	6.43047	0.4338	3.47	1.9462	1.2625	6.52500	0.10000	0.00781	6.3460
8"	8.6250	8	0.12500000	8.43359	1.0630	8.50	8.50003	1.7125	13.70	8.54063	0.6495	5.20	0.2500	2.00	8.41797	0.4338	3.47	2.1462	1.4625	8.52500	0.10000	0.00781	8.3335
10"	10.7500	8	0.12500000	10.54531	1.2100	9.68	10.62094	1.9250	15.40	10.66563	0.7150	5.72	0.2500	2.00	10.52969	0.4338	3.47	2.3587	1.6750	10.65000	0.10000	0.00781	10.4453
12"	12.7500	8	0.12500000	12.53281	1.3600	10.88	12.61781	2.1250	17.00	12.66563	0.7650	6.12	0.2500	2.00	12.51719	0.4338	3.47	2.5587	1.8750	12.65000	0.10000	0.00781	12.4328
14"	14.0000	8	0.12500000	13.77500	1.5620	12.50	13.87263	2.2500	18.00	13.91563	0.6880	5.50	0.2500	2.00	13.75938	0.4338	3.47	2.6837	2.0000	13.90000	0.10000	0.00781	13.6749
16"	16.0000	8	0.12500000	15.76250	1.8120	14.50	15.87575	2.4500	19.60	15.91563	0.6380	5.10	0.2500	2.00	15.74688	0.4338	3.47	2.8837	2.2000	15.90000	0.10000	0.00781	15.6624
18"	18.0000	8	0.12500000	17.75000	2.0000	16.00	17.87500	2.6500	21.20	17.91563	0.6500	5.20	0.2500	2.00	17.73438	0.4338	3.47	3.0837	2.4000	17.90000	0.10000	0.00781	17.6499
20"	20.0000	8	0.12500000	19.73750	2.1250	17.00	19.87031	2.8500	22.80	19.91563	0.7250	5.80	0.2500	2.00	19.72188	0.4338	3.47	3.2837	2.6000	19.90000	0.10000	0.00781	19.6374
24"	24.0000	8	0.12500000	23.71250	2.3750	19.00	23.86094	3.2500	26.00	23.91563	0.8750	7.00	0.2500	2.00	23.69688	0.4338	3.47	3.6837	3.0000	23.90000	0.10000	0.00781	23.6124

Thread basis

NPT is the American National Standard Taper Pipe Thread; the taper is 1 in 16 measured on the diameter (3/4 in per foot). Hand-tight engagement (L1) and effective external thread length (L2) are nominal ASME B1.20.1 gauge dimensions. Wrench-makeup turns beyond hand-tight are typically 2–3 turns; verify against the fitting maker and applicable make-up torque for the service. NPT provides thread sealing only with a thread sealant (tape or dope); it is not a self-sealing (metal-to-metal) thread.

L₃ is the internal-thread allowance beyond L₁ for wrench-tight engagement; L₄ is the overall external-thread length including vanish threads; L₅ is the complete external-thread length. E₀, E₁, E₂, E₃, and E₅ are pitch diameters at their corresponding reference planes. K₀ is the basic minor diameter at the small end of the pipe and is provided for tap-drill selection, not as a prescribed finished drill size.