What is the outside diameter of 1/2 inch pipe?

A 1/2″ pipe or NPT male thread is 0.840″ across the outside; 2″ pipe is 2.375″. The pipe size is a name, not a measurement.

How many threads per inch on 3/4 NPT?

14 threads per inch (3/4-14 NPT, ASME B1.20.1). 1/2″ is also 14; 1″ through 2″ are 11½.

What size drill for a 1/2 NPT tap?

A 23/32″ drill, per our pipe thread chart (drilled hole, no taper reamer).

How long is a 1/2 inch close nipple?

About 1-1/8″ (steel close nipple, per the Smith-Cooper and Anvil nipple charts) — threaded its whole length.

How far does a 1/2 NPT thread go in hand tight?

Hand-tight engagement L1 is 0.320″; the effective thread length L2 is 0.5337″ (ASME B1.20.1). The joint is then made up with a wrench.

What is the wall thickness of 1 inch Schedule 40 and Schedule 80 pipe?

Standard (Schedule 40): 0.133″. Extra heavy (Schedule 80): 0.179″. The OD is the same (1.315″); the heavier wall is on the inside.

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Pipe Thread Sizes (NPT)

NPT taper pipe threads 1/8″ to 6″: threads per inch, pipe OD, hand-tight engagement and thread length, tap drills, pipe and nipple walls, close nipple lengths.

An NPT thread (American National Standard Taper Pipe Thread, ASME B1.20.1) is the thread on pipe, nipples and threaded pipe fittings. It tapers 1 in 16 on the diameter (3/4″ per foot), so the male end wedges into the female as it is tightened. A pipe size is a name, not a measurement: a 1/2″ pipe is 0.840″ across the outside, and standard and extra heavy pipe of one size share that outside diameter — the heavier wall is on the inside. The thread is called out by size and threads per inch, as 1/2-14 NPT.

The letters match the table columns. L1 and L2 are measured from the end of the pipe. Not to scale.

NPT pipe thread sizes — ASME B1.20.1 (inches)
Pipe size	Threads per inch	Pipe OD (D)
1/8″	27	0.405″
1/4″	18	0.540″
3/8″	18	0.675″
1/2″	14	0.840″
3/4″	14	1.050″
1″	11½	1.315″
1-1/4″	11½	1.660″
1-1/2″	11½	1.900″
2″	11½	2.375″
2-1/2″	8	2.875″
3″	8	3.500″
3-1/2″	8	4.000″
4″	8	4.500″
5″	8	5.563″
6″	8	6.625″

D = outside diameter of the pipe, basic, inches — the size to measure on a male thread. A dash: our sources differ — give us a call.

Thread engagement — hand-tight and effective thread length
Pipe size	Hand-tight L1	Effective thread L2
1/8″	0.1615″	0.2639″
1/4″	0.2278″	0.4018″
3/8″	0.240″	0.4078″
1/2″	0.320″	0.5337″
3/4″	0.339″	0.5457″
1″	0.400″	0.6828″
1-1/4″	0.420″	0.7068″
1-1/2″	0.420″	0.7235″
2″	0.436″	0.7565″
2-1/2″	0.682″	1.1375″
3″	0.766″	1.2000″
3-1/2″	0.821″	1.2500″
4″	0.844″	1.3000″
5″	0.937″	1.4063″
6″	0.958″	1.5125″

Basic lengths, inches, from the end of the pipe (ASME B1.20.1). L1 = how far the threads engage screwed together by hand; L2 = the length of full-form thread on the male end.

Tap drills for NPT pipe taps
Thread	Tap drill
1/8-27 NPT	—
1/4-18 NPT	7/16″
3/8-18 NPT	37/64″
1/2-14 NPT	23/32″
3/4-14 NPT	59/64″
1-11½ NPT	1-5/32″
1-1/4-11½ NPT	1-1/2″
1-1/2-11½ NPT	1-47/64″
2-11½ NPT	2-7/32″
2-1/2-8 NPT	2-5/8″
3-8 NPT	3-1/4″
3-1/2-8 NPT	—
4-8 NPT	4-1/4″
5-8 NPT	—
6-8 NPT	—

Drill size for tapping without a taper pipe reamer. A dash: our sources differ (1/8″: letter R or Q) or only one lists it — give us a call. Drill decimals: drill size chart.

Pipe and nipple wall thickness — standard and extra heavy
Pipe size	OD	Standard (Sch 40)	Extra heavy (Sch 80)
1/8″	0.405″	0.068″	0.095″
1/4″	0.540″	0.088″	0.119″
3/8″	0.675″	0.091″	0.126″
1/2″	0.840″	0.109″	0.147″
3/4″	1.050″	0.113″	0.154″
1″	1.315″	0.133″	0.179″
1-1/4″	1.660″	0.140″	0.191″
1-1/2″	1.900″	0.145″	0.200″
2″	2.375″	0.154″	0.218″
2-1/2″	2.875″	0.203″	0.276″
3″	3.500″	0.216″	0.300″
3-1/2″	4.000″	0.226″	0.318″
4″	4.500″	0.237″	0.337″
5″	5.563″	0.258″	0.375″
6″	6.625″	0.280″	0.432″

Nominal wall, inches, steel and stainless pipe (ASME B36.10 / B36.19). Brass pipe walls differ and aren’t on this chart.

Close nipple lengths — steel pipe nipples
Pipe size	Close nipple length
1/8″	3/4″
1/4″	7/8″
3/8″	1″
1/2″	1-1/8″
3/4″	1-3/8″
1″	1-1/2″
1-1/4″	1-5/8″
1-1/2″	1-3/4″
2″	2″
2-1/2″	2-1/2″
3″	2-5/8″
3-1/2″	—
4″	2-7/8″
5″	—
6″	—

Nominal overall length, inches, per the Smith-Cooper and Anvil steel nipple charts. A dash: only one of our sources lists it — give us a call.

Good to know

NPT seals with a sealant. The taper makes the joint tight, but an NPT joint is made pressure-tight with a thread sealant — pipe dope or PTFE tape on the male thread. Screw it in by hand, then make it up with a wrench.

Size a thread by its outside diameter. Measure across the outside of a male thread (or a pipe end) and find the OD in the table; the pipe size and threads per inch are on the same row. Several sizes share a thread count, so the OD is what tells them apart.

Quick answers

What is the outside diameter of 1/2 inch pipe?: A 1/2″ pipe or NPT male thread is 0.840″ across the outside; 2″ pipe is 2.375″. The pipe size is a name, not a measurement.
How many threads per inch on 3/4 NPT?: 14 threads per inch (3/4-14 NPT, ASME B1.20.1). 1/2″ is also 14; 1″ through 2″ are 11½.
What size drill for a 1/2 NPT tap?: A 23/32″ drill, per our pipe thread chart (drilled hole, no taper reamer).
How long is a 1/2 inch close nipple?: About 1-1/8″ (steel close nipple, per the Smith-Cooper and Anvil nipple charts) — threaded its whole length.
How far does a 1/2 NPT thread go in hand tight?: Hand-tight engagement L1 is 0.320″; the effective thread length L2 is 0.5337″ (ASME B1.20.1). The joint is then made up with a wrench.
What is the wall thickness of 1 inch Schedule 40 and Schedule 80 pipe?: Standard (Schedule 40): 0.133″. Extra heavy (Schedule 80): 0.179″. The OD is the same (1.315″); the heavier wall is on the inside.

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