Garden Hose Thread Size Chart: GHT, NPT, M22 & BSP

Every "this adapter does not fit" problem starts with the same confusion: the size printed on a fitting is almost never the size you measure with a caliper. A 3/4" garden hose thread is not 3/4" across. A 3/4" pipe thread is not either — and the two are within twelve thousandths of an inch of each other while being completely incompatible.

This page is the reference to bookmark. Measure first, look up second, buy once.

The Master Chart

Measure outside diameter of the male threads with a caliper, then count threads per inch (or measure the pitch in millimetres). Those two numbers identify almost every fitting you will meet in a garden, on an RV, or behind a pressure washer.

Thread standard	Nominal size	Actual male OD	TPI	Pitch	Tapered?	Seals with
GHT (garden hose)	3/4"	1.0625" / 26.99 mm	11.5	2.21 mm	No — parallel	Rubber washer
GHT	5/8"	0.9375" / 23.81 mm	11.5	2.21 mm	No — parallel	Rubber washer
NPT (pipe)	1/2"	0.840" / 21.34 mm	14	1.81 mm	Yes — 1:16	PTFE tape / dope
NPT	3/4"	1.050" / 26.67 mm	14	1.81 mm	Yes — 1:16	PTFE tape / dope
NPT	1"	1.315" / 33.40 mm	11.5	2.21 mm	Yes — 1:16	PTFE tape / dope
NPS (straight pipe)	1/2"	0.840" / 21.34 mm	14	1.81 mm	No — parallel	Washer or gasket
NPS	3/4"	1.050" / 26.67 mm	14	1.81 mm	No — parallel	Washer or gasket
BSPP (British)	G 3/4"	26.44 mm	14	1.81 mm	No — parallel	Washer or O-ring
M22 (pressure washer)	M22 × 1.5	22.0 mm	—	1.5 mm	No — parallel	O-ring / washer

Figures are nominal per ASME B1.20.7 (GHT) and B1.20.1 (NPT/NPS). Real parts run a thousandth or two either way — always confirm by thread pitch, never by diameter alone.

Why 3/4" GHT and 3/4" NPT Drive Everyone Crazy

Look at the chart again: 3/4" GHT measures 1.0625" and 3/4" NPT measures 1.050". They differ by 0.0125 inch — about the thickness of three sheets of paper. Hold the two side by side and they look identical.

They are not. GHT runs at 11.5 threads per inch; NPT runs at 14. Start threading one into the other and you get about two turns of suspiciously easy movement, then it binds, then it either strips or jams crooked. If you force it, you ruin both parts.

There is a second difference that matters more in practice: GHT is parallel and seals with a washer; NPT is tapered and seals with thread sealant. Even if the pitch matched, a tapered thread in a straight coupling would bottom out before sealing.

The practical takeaway: never adapt by force, and never adapt with tape. Match the thread, then seal it the way that thread is designed to seal. Our full walkthrough on how to tell GHT from NPT covers the visual tells; the NPT-to-GHT adapter collection covers the real conversions.

How to Identify a Thread in Three Steps

Step 1 — Measure the outside diameter

Close a caliper across the crest of the male threads. If you do not own calipers, a printable thread gauge works, or compare against a known fitting. Write down the number in millimetres — millimetres are easier to match against the chart than fractional inches.

Step 2 — Get the pitch

Count how many thread crests fall in one inch and divide: 11.5 TPI means you count 11 or 12 crests in an inch. Alternatively lay a ruler across the threads and measure crest-to-crest in millimetres — 2.21 mm is GHT, 1.81 mm is NPT/NPS/BSP, 1.5 mm is M22.

Step 3 — Decide tapered or straight

Run a caliper along the length: measure the OD near the end and again four or five threads back toward the shoulder. If the number grows, it is tapered (NPT). If it stays the same, it is parallel (GHT, NPS, BSPP, M22).

Only if both diameter and pitch and taper match should the two parts be threaded together.

Common Conversions and the Part That Does Them

You have	You need	Use
3/4" GHT male (hose end)	1/2" NPT male (pipe)	3/4" GHT male to 1/2" NPT male adapter
3/4" GHT male (hose end)	3/4" NPT male (pipe)	3/4" GHT male to 3/4" NPT male adapter
3/4" GHT female (coupling)	3/4" NPT female (pipe)	GHT female to NPT female adapter
Shallow well pump, 1" NPT	Standard garden hose	1" NPT male to 3/4" GHT male adapter
Pressure washer gun, M22	3/4" GHT hose	M22 female to 3/4" GHT male adapter
Pressure washer hose, M22	3/4" GHT female	M22 female to 3/4" GHT female adapter
Hose bib	1/4" drip irrigation tubing	GHT to 1/4" tubing adapter

Unsure which direction you need? Browse by thread family instead: everything with hose threads lives in GHT connectors and couplers, and everything that crosses to pipe threads lives in adapters, fittings and valves.

Sizes People Get Wrong

• "3/4 inch" on a hose is the bore, not the thread. The thread is 1-1/16" across. Ordering by the number on the box instead of the measured diameter is the single biggest source of wrong parts.
• 5/8" hoses still use 3/4" GHT couplings. The 5/8" refers to the tube bore; the fitting is standard GHT on almost all US residential hoses.
• M22 comes in two flavours. M22 with a 14 mm bore and M22 with a 15 mm bore look the same and do not always interchange. Measure the bore, not just the thread.
• BSP fittings are not NPT. British and European equipment often uses BSPP at 14 TPI — the same pitch as NPT but a different thread angle (55° vs 60°) and a different diameter. They will start and then weep.
• Barb sizes are hose bore, not thread. A 5/8" barb goes inside a 5/8" hose and still ends in a standard 3/4" GHT coupling.

Two Places the Chart Matters Most

RV utility bays

An RV wet bay is the hardest place on earth to connect a hose, because the thread is rarely the actual problem — clearance is. Even when you have identified the thread correctly, a coupling that cannot be squared up against the spigot will not seal, and you will chase a phantom leak for an afternoon. The fix is geometry rather than thread conversion: an elbow moves the connection out where a wrench can reach it. A 45° brass elbow handles a shallow offset, and a 90° elbow handles a spigot that sits flush to a wall. Both keep full flow, which matters when you are running a blow-out or filling a fresh tank on a schedule.

Pressure washer hookups

Pressure washer connections are the other repeat offender, because three standards show up on the same machine. The pump inlet is usually standard 3/4" GHT. The gun or lance side is frequently M22 × 1.5. And some commercial units use quick-connect couplers on top of whichever thread the machine shipped with. Before ordering, check whether your M22 fitting has a 14 mm or 15 mm bore — the thread is identical and the bore is not, and a mismatched bore will seat and then weep under pressure. If you are connecting a washer to a standard hose, start with the M22 to 3/4" GHT adapter rather than improvising with tape.

Frequently Asked Questions

What size thread is a standard garden hose?

3/4" GHT, also written 3/4-11.5 NH. The measured outside diameter of the male thread is 1.0625" (26.99 mm) at 11.5 threads per inch, and it is a straight thread that seals with a rubber washer.

Is 3/4" GHT the same as 3/4" NPT?

No. The diameters are within 0.0125" of each other, but GHT is 11.5 TPI parallel and NPT is 14 TPI tapered. They will not seal together and can damage each other if forced.

Why does my hose fit the faucet but not the pipe?

Outdoor faucets are made with hose threads on the spout; plumbing pipe is NPT. You need an adapter that converts thread family, not just diameter — see the conversion table above.

Do I need Teflon tape on garden hose threads?

No. GHT seals with the washer inside the coupling. Tape adds bulk, stops the coupling seating fully, and sheds debris into nozzles. Tape belongs on tapered NPT threads.