What is the outside diameter of 3/4 copper pipe?

0.875 in, for Type K, L and M alike. Copper tube's outside diameter is always the size plus 1/8 in, per the Copper Tube Handbook.

What is the inside diameter of 3/4 PEX?

0.671 in for PEX CTS SDR 9, worked from IPC Table E202.1. 3/4 in Type L copper is 0.785 in, so the PEX has about 73% of the copper's flow area.

What is the difference between Type K, L and M copper?

Wall thickness. At 3/4 in the walls are 0.065, 0.045 and 0.032 in, so the bores are 0.745, 0.785 and 0.811 in. The outside diameter is the same, 0.875 in.

How many gallons are in 100 feet of pipe?

3/4 in Type L copper holds 2.51 gallons per 100 ft and 1/2 in Type L holds 1.21. The calculator gives it for every pipe here.

Is 1/2 inch pipe really 1/2 inch?

No. 1/2 in copper is 0.625 in outside and 0.545 in inside in Type L. The size is a name, not a measurement.

Is CPVC the same size as copper?

CTS CPVC is: it shares copper's outside diameter. Schedule 40 and 80 CPVC are iron pipe size, which is larger outside and does not fit copper fittings.

Home › Plumbing › Pipe Size Chart

Pipe Size Chart

CDA Copper Tube Handbook Tables 14.2a to 14.2c, and IPC Table E202.1 for plastic

A 3/4 in PEX pipe and a 3/4 in copper pipe are not the same size inside. PEX's bore is 0.671 in and Type L copper's is 0.785 in, so the PEX carries 27% less area, about the bore of 5/8 in copper. The chart below gives outside and inside diameters, wall thickness and water volume for copper from the Copper Development Association's handbook, and inside diameters for PEX, CPVC and PE-RT worked from the plumbing code's own water-weight table.

Look up a pipe

Pipe

Copper size

Plastic nominal size

Flow, for velocity (zero to skip)

gpm

Copper uses the copper size list; the plastics use the nominal size list.

Specification summary

Generated from on . Reopen that address to reproduce these figures exactly.

Entered

Result

Worked example

3/4 in Type L copper against 3/4 in PEX, at 8 gpm.

Copper. OD 0.875 in, ID 0.785 in, wall 0.045 in, 2.51 gal per 100 ft (Table 14.2b).
PEX. Bore 0.671 in from IPC Table E202.1.
Velocity at 8 gpm. 5.3 ft/s in the copper, 7.3 ft/s in the PEX.

The same flow runs 37% faster in the PEX, because its bore is smaller.

The formula

Copper is read from the handbook. Plastic bore is worked back from the water per foot:

bore = √(fluid ounces per ft × 1.8047 × 4 ÷ (12 × π)) velocity = gpm × 0.3208 ÷ area in sq in

1.8047: cubic inches in a US fluid ounce
0.3208: converts gpm and square inches to feet per second

Copper outside diameter is always the size plus 1/8 in; the handbook says so.

Where the numbers come from

Copper is the Copper Development Association's Copper Tube Handbook, publication A4015-26/24, Tables 14.2a, 14.2b and 14.2c.

Plastic bores are worked from IPC 2018 Table E202.1, read as adopted in San Antonio, which prints the water each foot of pipe holds. Run the same arithmetic on its copper rows and it reproduces the handbook's inside diameters for all 18 copper cells to within 0.001 in, which is why the method is trusted for the plastics.

Copper tube: Type K, L and M

CDA Copper Tube Handbook Tables 14.2a to 14.2c, inches; volume from Table 14.2b
Size	OD	ID Type K	ID Type L	ID Type M	Wall K	Wall L	Wall M	Type L gal per 100 ft
1/4 in	0.375	0.305	0.315	-	0.035	0.030	-	0.40
3/8 in	0.500	0.402	0.430	0.450	0.049	0.035	0.025	0.75
1/2 in	0.625	0.527	0.545	0.569	0.049	0.040	0.028	1.21
5/8 in	0.750	0.652	0.666	-	0.049	0.042	-	1.74
3/4 in	0.875	0.745	0.785	0.811	0.065	0.045	0.032	2.51
1 in	1.125	0.995	1.025	1.055	0.065	0.050	0.035	4.29
1 1/4 in	1.375	1.245	1.265	1.291	0.065	0.055	0.042	6.55
1 1/2 in	1.625	1.481	1.505	1.527	0.072	0.060	0.049	9.25
2 in	2.125	1.959	1.985	2.009	0.083	0.070	0.058	16.10
2 1/2 in	2.625	2.435	2.465	2.495	0.095	0.080	0.065	24.80
3 in	3.125	2.907	2.945	2.981	0.109	0.090	0.072	35.40
3 1/2 in	3.625	3.385	3.425	3.459	0.120	0.100	0.083	47.80
4 in	4.125	3.857	3.905	3.935	0.134	0.110	0.095	57.10
5 in	5.125	4.805	4.875	4.907	0.160	0.125	0.109	97.10
6 in	6.125	5.741	5.845	5.881	0.192	0.140	0.122	139.00
8 in	8.125	7.583	7.725	7.785	0.271	0.200	0.170	244.00
10 in	10.125	9.449	9.625	9.701	0.338	0.250	0.212	378.00
12 in	12.125	11.315	11.565	11.617	0.405	0.280	0.254	545.00

The outside diameter is the same for all three types at a given size, always 1/8 in more than the size. What changes is the wall: K is thickest, M thinnest, so a Type M pipe has the largest bore. A dash means the handbook lists no Type M at 1/4 or 5/8 in.

PEX, CPVC and PE-RT inside diameters

Bore in inches worked from IPC Table E202.1 water weights
Nominal	PEX CTS SDR 9	CPVC CTS SDR 11	CPVC Sch 40	CPVC Sch 80	PE-RT SDR 9	PEX-AL-PEX
3/8 in	0.350	-	0.473	-	0.350	0.347
1/2 in	0.475	0.489	0.602	0.529	0.475	0.501
3/4 in	0.671	0.715	0.804	0.724	0.671	0.806
1 in	0.865	0.921	1.029	0.935	0.865	1.032
1 1/4 in	1.055	1.125	1.360	1.256	1.055	1.275
1 1/2 in	1.245	1.329	1.590	1.476	1.245	1.630
2 in	1.629	1.739	2.047	1.913	1.629	2.028

CTS means copper tube size: the plastic is made to copper's outside diameter so it fits the same fittings, and the thicker plastic wall comes out of the bore. At 3/4 in, PEX's 0.671 in bore is 73% of Type L copper's area, almost exactly the 0.666 in bore of 5/8 in Type L. That is why the plumbing code's sizing tables step PEX up a size where copper would not need it.

Schedule 40 and 80 CPVC are iron pipe size, a larger outside diameter, which is why their bores run bigger than the CTS column at the same nominal size.

One volume in the handbook does not fit its own bore

Every row of the handbook's copper tables was checked three ways: outside diameter minus two walls against the inside diameter, the bore against the printed area, and the area against the printed volume. All pass except two volumes in the Type L table, 14.2b.

4 in Type L is printed at 0.571 gallons per foot. Its own 3.905 in bore holds 0.622, and the table gives 4 in Type K, which has a smaller bore, 0.608. A thicker pipe cannot hold more water, so the Type L figure is the one that is wrong. 5/8 in Type L is printed at 0.0174 against 0.0181 from its bore.

The calculator flags both when you pick them. For anything measured by volume, such as how long hot water takes to arrive, use the bore.

Frequently asked questions

What is the outside diameter of 3/4 copper pipe?: 0.875 in, for Type K, L and M alike. Copper tube's outside diameter is always the size plus 1/8 in, per the Copper Tube Handbook.
What is the inside diameter of 3/4 PEX?: 0.671 in for PEX CTS SDR 9, worked from IPC Table E202.1. 3/4 in Type L copper is 0.785 in, so the PEX has about 73% of the copper's flow area.
What is the difference between Type K, L and M copper?: Wall thickness. At 3/4 in the walls are 0.065, 0.045 and 0.032 in, so the bores are 0.745, 0.785 and 0.811 in. The outside diameter is the same, 0.875 in.
How many gallons are in 100 feet of pipe?: 3/4 in Type L copper holds 2.51 gallons per 100 ft and 1/2 in Type L holds 1.21. The calculator gives it for every pipe here.
Is 1/2 inch pipe really 1/2 inch?: No. 1/2 in copper is 0.625 in outside and 0.545 in inside in Type L. The size is a name, not a measurement.
Is CPVC the same size as copper?: CTS CPVC is: it shares copper's outside diameter. Schedule 40 and 80 CPVC are iron pipe size, which is larger outside and does not fit copper fittings.

Check these numbers yourself

The Copper Tube Handbook, CDA Publication A4015-26/24Copper Development Association, 2026. Tables 14.2a, 14.2b and 14.2c, dimensions and volume of Type K, L and M tube, and the statement that outside diameter is always 1/8 in larger than the size. Read 2026-09-30.
IPC 2018 Appendix E, Table E202.1, as adopted in San AntonioInternational Plumbing Code 2018 as adopted in San Antonio, read through UpCodes. Table E202.1, fluid ounces of water per foot of pipe by material and size. Read 2026-09-13.

How every figure here is verified: Sources & Method. Who builds this: Lucas Pradella, and the method is on About. Found something wrong? Tell us and it gets fixed or removed.

Figures on this page last checked against the source documents on 2026-09-30. Codes are amended locally; confirm against the edition your jurisdiction enforces.

Related calculators

Nominal dimensions. Manufacturing tolerances apply; a fitting maker's data sheet governs the fit.