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Pipe Size Chart
Quick answer: Nominal pipe size is a label, not a measurement. A 1″ pipe has a 1.315″ OD and a 1.049″ bore in Schedule 40. The OD stays fixed across schedules so fittings interchange — only the wall thickness and bore change.
Outside diameter, wall thickness and inside diameter for every common pipe size in Schedule 40 and 80, plus copper tube dimensions and what the size difference does to flow.
Nominal pipe size (NPS) chart
The single most confusing thing about pipe: the nominal size is not a measurement of anything. A “1 inch” pipe has a 1.315″ outside diameter and a 1.049″ inside diameter. Neither is one inch. The name is a legacy label, and the outside diameter is what stays fixed so fittings interchange across wall thicknesses.
| NPS | OD (in) | Sch 40 wall | Sch 40 ID | Sch 80 wall | Sch 80 ID |
|---|---|---|---|---|---|
| 1/8 | 0.405 | 0.068 | 0.269 | 0.095 | 0.215 |
| 1/4 | 0.540 | 0.088 | 0.364 | 0.119 | 0.302 |
| 3/8 | 0.675 | 0.091 | 0.493 | 0.126 | 0.423 |
| 1/2 | 0.840 | 0.109 | 0.622 | 0.147 | 0.546 |
| 3/4 | 1.050 | 0.113 | 0.824 | 0.154 | 0.742 |
| 1 | 1.315 | 0.133 | 1.049 | 0.179 | 0.957 |
| 1-1/4 | 1.660 | 0.140 | 1.380 | 0.191 | 1.278 |
| 1-1/2 | 1.900 | 0.145 | 1.610 | 0.200 | 1.500 |
| 2 | 2.375 | 0.154 | 2.067 | 0.218 | 1.939 |
| 2-1/2 | 2.875 | 0.203 | 2.469 | 0.276 | 2.323 |
| 3 | 3.500 | 0.216 | 3.068 | 0.300 | 2.900 |
| 4 | 4.500 | 0.237 | 4.026 | 0.337 | 3.826 |
| 6 | 6.625 | 0.280 | 6.065 | 0.432 | 5.761 |
| 8 | 8.625 | 0.322 | 7.981 | 0.500 | 7.625 |
Every row satisfies OD − (2 × wall) = ID. Schedule 80 has the same outside diameter as Schedule 40 — the extra wall thickness comes out of the bore, which is why Sch 80 flows less.
Copper is measured differently again
| Nominal | Actual OD | Type M wall | Type L wall | Type K wall |
|---|---|---|---|---|
| 1/2″ | 0.625″ | 0.028″ | 0.040″ | 0.049″ |
| 3/4″ | 0.875″ | 0.032″ | 0.045″ | 0.065″ |
| 1″ | 1.125″ | 0.035″ | 0.050″ | 0.065″ |
| 1-1/4″ | 1.375″ | 0.042″ | 0.055″ | 0.065″ |
| 1-1/2″ | 1.625″ | 0.049″ | 0.060″ | 0.072″ |
| 2″ | 2.125″ | 0.058″ | 0.070″ | 0.083″ |
Copper tube OD is always nominal + 1/8″. Type M is thinnest and cheapest (interior supply), Type L is standard for most potable water, Type K is thickest and used underground.
Choosing a schedule
- Schedule 40 PVC — the residential default for drain, waste and vent, irrigation, and cold water supply. White.
- Schedule 80 PVC — higher pressure rating, thicker wall, smaller bore. Grey. Used where pressure or physical abuse demands it.
- CPVC — rated for hot water where PVC is not. Usually cream or yellow.
- Schedule 40 steel — gas lines, structural handrail, compressed air.
Flow capacity falls off fast
Flow is roughly proportional to the bore area, and area goes with the square of the radius. Halving the diameter cuts flow to a quarter, before friction is even considered. It is why stepping a 3/4″ supply down to 1/2″ for a long run costs so much more pressure than the size difference suggests.
| NPS | Sch 40 ID | Bore area (sq in) | Relative to 1/2″ |
|---|---|---|---|
| 1/2″ | 0.622″ | 0.304 | 1.0× |
| 3/4″ | 0.824″ | 0.533 | 1.8× |
| 1″ | 1.049″ | 0.864 | 2.8× |
| 1-1/2″ | 1.610″ | 2.036 | 6.7× |
| 2″ | 2.067″ | 3.356 | 11.0× |
Frequently asked questions
What is the actual outside diameter of 1 inch pipe?
1.315 inches. Nominal pipe size is a label, not a measurement — a 1 in NPS pipe has a 1.315 in OD and, in Schedule 40, a 1.049 in inside diameter.
What is the difference between Schedule 40 and Schedule 80?
Wall thickness. Both have identical outside diameters so they share fittings, but Schedule 80 has a thicker wall and therefore a smaller bore. In 1 in pipe, Sch 40 has a 1.049 in ID while Sch 80 has 0.957 in.
Is copper pipe measured by inside or outside diameter?
Neither exactly. Copper tube is sold by a nominal size, and the actual outside diameter is always nominal plus 1/8 in — so 1/2 in copper has a 0.625 in OD. The wall thickness then varies by type M, L or K.
Can I use PVC for hot water?
No. Standard white Schedule 40 PVC softens well below household hot-water temperature and is not rated for it. Use CPVC, PEX or copper for hot supply lines.