Quick answer
A plumbing pipe schedule is a standard number, such as Schedule 40 or Schedule 80, that sets how thick a pipe’s wall is for a given nominal size, while the outside diameter stays the same, so a higher schedule means a thicker wall, a smaller inside bore and a higher pressure rating.
Schedules apply to iron pipe size (IPS) pipe such as steel, PVC and ABS. Copper tube uses Types K, L and M instead.
Quick facts
The key facts about Plumbing Pipe Schedule, with sources:
- What stays fixed
- Outside diameter, so fittings fit across schedules 1
- Common plastic schedules
- PVC Schedule 40, 80 and 120 (ASTM D1785) 2
- 2-inch PVC example
- Sch 40: 0.154 in wall; Sch 80: 0.218 in wall 1
- Heat matters
- PVC pressure ratings fall with temperature; max 140°F 1
- Copper instead
- Types K, L and M wall series, not schedules 5
Key takeaways
- Pipe schedule is a wall-thickness series; the higher the number, the thicker the wall.
- The outside diameter stays the same across schedules, so the inside gets smaller as the wall grows.
- A higher schedule usually means a higher pressure rating, but larger sizes rate lower.
- Plastic pipe ratings drop as water gets hotter; PVC tops out at 140°F per one maker’s spec.
- Copper tube does not use schedules; it uses Types K, L and M.
What a pipe schedule number measures
Pipe is named by a nominal size, such as 2-inch, that is not its actual measured diameter.
ASME’s steel pipe standard notes that for pipe 12 inches and smaller, the outside diameter is numerically larger than the size name 4.
A 2-inch PVC pipe, for example, has an outside diameter of 2.375 inches 1.
The schedule then sets the wall. ASTM D1785 covers PVC pipe made in Schedule 40, 80 and 120 sizes and pressure-rated for water 2.
Because the outside diameter is fixed by size, a thicker wall eats into the inside.
A Harrison Plastic spec lists 2-inch Schedule 40 PVC with a 2.047-inch average inside diameter and Schedule 80 with 1.913 inches 1.
That is why a Schedule 40 fitting and a Schedule 80 pipe of the same size can fit together: the outside matches. The difference is wall strength, inside flow area and pressure rating.
How to read a pipe’s schedule and rating
- Find the print line: Plastic pipe is marked along its length with material, size, schedule and standard, such as "PVC Sch 40 ASTM D1785" 2.
- Note the nominal size: This sets the outside diameter, not the inside 4.
- Note the schedule: This sets the wall and inside diameter 1.
- Look up the pressure rating: Ratings depend on schedule and size; one maker lists 2-inch Sch 40 PVC at 280 psi and Sch 80 at 400 psi at 73°F 1.
- Adjust for heat: Multiply by the maker’s temperature factor if the water is warmer than 73°F 1.
- Check the use: Pressure pipe, drain pipe and threaded joints each have their own rules 26.
Max working pressure at temperature = Rated pressure at 73°F × Derating factor
Rated pressure at 73°F- From the maker’s table for that size and schedule
Derating factor- 1.00 at 73°F down to 0.22 at 140°F in one maker’s table
Harrison Plastic’s own example: 10-inch Schedule 80 PVC at 120°F is 230 psi × 0.40 = 92 psi 1.
Source: [1]
Which schedules and wall systems appear in home plumbing
| System | Used for | Standard |
|---|---|---|
| PVC Schedule 40 | Pressure pipe and drain pipe | ASTM D1785 (pressure) 2 |
| PVC Schedule 80 | Higher pressure and threaded joints | ASTM D1785 2 |
| PVC Schedule 120 | Heaviest common PVC wall | ASTM D1785 2 |
| ABS Schedule 40 DWV | Drain, waste and vent lines | ASTM D2661 3 |
| Steel pipe schedules | Steel and galvanized pipe | ASME B36.10M dimensions 4 |
| Copper Types K, L, M | Copper water tube; not schedules | Copper Tube Handbook 5 |
Example: 2-inch PVC, Schedule 40 vs Schedule 80
All figures are from Harrison Plastic’s published Schedule 40 and 80 PVC dimension tables, for water at 73°F, non-shock 1.
| Measure | Schedule 40 | Schedule 80 |
|---|---|---|
| Outside diameter | 2.375 in 1 | 2.375 in 1 |
| Average inside diameter | 2.047 in 1 | 1.913 in 1 |
| Minimum wall | 0.154 in 1 | 0.218 in 1 |
| Weight per foot | 0.720 lb 1 | 0.984 lb 1 |
| Max working pressure, 73°F | 280 psi 1 | 400 psi 1 |
| Max working pressure, 120°F (× 0.40) | 112 psi | 160 psi |
Three lessons. The outside is identical, so fittings interchange by size. Schedule 80 gives up about 0.13 inch of inside diameter for a wall about 40 percent thicker (0.218 vs 0.154).
And heat cuts the rating hard: at 120°F both pipes keep only 40 percent of their room-temperature rating, by the same maker’s factor 1. The 120°F row is our arithmetic from those published figures.
Where the schedule shows up on pipe and on quotes
Look at the print line on PVC, ABS and steel pipe in a basement, crawlspace or under a sink. ABS drain pipe is made to Schedule 40 iron pipe sizes under ASTM D2661 3. PVC pressure and drain pipe are often marked Schedule 40 or 80.
On a quote, you may see "Sch 40 PVC" for a drain line or irrigation main, or "Sch 80" for a threaded nipple, a pump connection or exposed pipe. Our pipe materials guide compares the materials themselves.
You will not see schedule on copper or PEX. Copper is sold by Type K, L or M 5. PEX uses its own copper-tube-size system with a dimension ratio instead of a schedule.
What a heavier schedule gains and gives up
What a heavier schedule gives
What a schedule number does not tell you
Schedule alone does not give a pressure rating, because the rating falls as the pipe gets bigger even though the schedule stays the same.
In Harrison’s Schedule 40 PVC table the wall grows from 0.109 inch at 1/2-inch to 0.280 inch at 6-inch, but the bore grows faster, so the rating drops from 590 psi to 180 psi 1.
Ratings also change with temperature, as the chart above shows, and with material.
The four figures below come straight from that table. Read them as a warning against assuming a big Schedule 40 main is as strong as the small Schedule 40 nipple on the same job.
It also does not tell you what the pipe is approved for. ASTM D1785 covers PVC pipe pressure-rated for water 2, while drain pipe is made to other standards.
Plumbing codes list which standards each use allows; a pipe that is the right schedule can still be the wrong material for hot water or for drinking water.
And it does not tell you copper wall thickness, because copper uses Types K, L and M, with Type K the thickest and Type M the thinnest for any size 5.
- 590 psi1/2-inch0.109-in minimum wall
- 280 psi2-inch0.154-in minimum wall
- 220 psi4-inch0.237-in minimum wall
- 180 psi6-inch0.280-in minimum wall
Water, non-shock, at 73°F; one manufacturer’s table. Source: [1]
What drives the cost of a heavier schedule
We do not list prices; fair numbers need dated local quotes.
A heavier schedule uses more material per foot, so the pipe and fittings cost more. On most home jobs, labor, access and fittings count for more than the pipe itself.
Drivers include the length of run, pipe size, whether threaded or solvent joints are used, whether the line is buried or exposed, and whether code requires a heavier wall for that use.
For how plumbing quotes are built, see our plumbing cost guide, and for whole-house supply lines see our repipe cost estimator.
How a plumber chooses a schedule
- Start with the use: Drain, vent, pressure water, buried service or exposed line.
- Check the code: Which materials and standards are listed for that use where you live 6.
- Check pressure and temperature: Apply the maker’s derating if the water is warm 1.
- Check joints: Threaded plastic joints need Schedule 80 or heavier 61.
- Check flow: A thicker wall shrinks the bore; size up if needed. Our fixture unit calculator helps estimate demand.
- Match fittings: Use fittings rated for the same schedule and pressure.
How to keep scheduled pipe within its rating
- Keep the print line visible where you can; it is the record of what was installed.
- Do not run plastic pressure pipe above its rated temperature; PVC’s max is 140°F in Harrison’s spec 1.
- Avoid threading Schedule 40 plastic; Harrison says the wall is too thin 1.
- Support plastic pipe as the maker directs so it does not sag.
- When repairing, match size, schedule and material.
Which pipe problems need a plumber
- Threaded Schedule 40 plastic fittings that weep or crack.
- PVC pressure pipe on a hot water line, or near a water heater.
- Plastic pipe that is soft, bulging or discolored near heat.
- Pipe with no print line on a pressure line, so its rating is unknown.
- Repairs that mix schedules or materials with no listed transition.
Pressure, heat and burst risk
Plastic pipe used above its pressure or temperature rating can split without warning. Harrison’s spec puts PVC’s maximum service temperature at 140°F and cuts its rating to 22 percent at that heat 1.
Never use PVC pressure pipe on a water heater outlet or a relief valve discharge unless the code and maker allow it, and never cap a relief valve line.
For a leak or burst, see our plumbing emergencies guide.
Which standards and codes set pipe schedules
ASTM D1785: PVC plastic pipe, Schedules 40, 80 and 120, pressure-rated for water; covers dimensions, sustained pressure, burst and marking 2.
ASTM D2661: ABS Schedule 40 drain, waste and vent pipe and fittings 3.
ASME B36.10M: dimensions of wrought steel pipe, welded or made without a seam; for pipe 12 inches and smaller, outside diameters are larger than the size number 4.
California Plumbing Code, 2025 edition (in force 1 January 2026), §705.1.3: threaded ABS joints need a minimum of Schedule 80 pipe, unchanged from 2022 6. Other materials and codes have their own rules; check the code your jurisdiction adopted.
How schedule compares with copper types and nominal size
| System | What it controls | Main difference |
|---|---|---|
| Pipe schedule (Sch 40, 80) | Wall thickness at a fixed outside diameter 1 | Used for IPS pipe: steel, PVC, ABS |
| Copper Type K, L, M | Wall thickness; OD is size plus 1/8 inch 5 | Separate system for copper tube |
| ABS DWV | Schedule 40 iron pipe size walls 3 | A drain product, not rated like pressure pipe |
| Nominal size | The name, such as 2-inch | Not the actual inside or outside measure 4 |
What people get wrong about pipe schedules
- Myth A 2-inch pipe is 2 inches across.
- Reality 2-inch iron pipe size measures 2.375 inches outside 1.
- Myth Schedule 80 has a bigger outside diameter.
- Reality Outside diameter is the same; the inside shrinks 1.
- Myth Schedule 40 PVC is rated the same at every size.
- Reality One maker lists 590 psi at 1/2-inch and 220 psi at 4-inch 1.
- Myth Any plastic pipe can be threaded.
- Reality Thread only Schedule 80 or heavier, per Harrison and California’s ABS rule 16.
- Myth Copper has schedules too.
- Reality Copper uses Types K, L and M 5.
How local codes and climate change the schedule choice
Codes decide which schedule and material each job needs, and they vary by state. California’s code, for example, requires Schedule 80 or heavier for threaded ABS joints 6.
Climate matters too: a buried line in a hot climate or a line near a water heater sees warmer water, and PVC loses rating fast with heat 1.
Ask your building department which standards it accepts for a buried water service or drain.
When pipe schedule matters to you and what to buy
It matters when you buy repair parts, when a quote names a schedule, or when a line will carry pressure, heat or threads. Match the size, schedule and material of what is there, and check the rating at your water temperature.
For drain work, Schedule 40 is common; for threaded plastic and higher pressure, Schedule 80. For supply lines, the material choice usually matters more than the schedule; our repiping service page covers that choice. The guide below sorts the five situations homeowners meet most.
Questions about Plumbing Pipe Schedule
What schedule pipe is used in residential plumbing?
Drain, waste and vent lines are usually Schedule 40 plastic, such as ABS made to ASTM D2661 or PVC DWV.
Schedule 80 shows up where plastic is threaded or needs a higher rating, such as pump connections.
Most supply lines in homes are copper, PEX or CPVC, which use their own sizing systems rather than schedules.
What is the difference between Schedule 40 and Schedule 80?
Schedule 80 has a thicker wall than Schedule 40 at the same size. For 2-inch PVC, one maker lists a 0.154-inch wall and 280 psi rating for Schedule 40 versus 0.218 inch and 400 psi for Schedule 80, at 73°F. Both have a 2.375-inch outside diameter, so they use the same fittings.
Can Schedule 40 and Schedule 80 fittings be mixed?
They fit, because the outside diameter is the same for a given size. The joint’s pressure rating is limited by its weakest part, so a Schedule 40 fitting on Schedule 80 pipe lowers the rating. Match parts to the pressure the line needs and follow your code.
Is Schedule 40 PVC good for hot water?
No. PVC loses pressure rating quickly as water warms. Harrison Plastic’s derating table drops PVC to 40 percent of its rating at 120°F and 22 percent at 140°F, its maximum service temperature. Hot water lines use materials rated for heat, such as CPVC, PEX or copper.
Why is 2-inch pipe not 2 inches?
Pipe sizes are nominal names, not measurements. ASME’s steel pipe standard notes that pipe 12 inches and smaller has an outside diameter larger than its size number. A 2-inch iron pipe size has a 2.375-inch outside diameter, and its inside depends on the schedule.
Does copper pipe have a schedule?
No. Copper water tube uses Types K, L and M. The Copper Tube Handbook says the outside diameter is always 1/8 inch larger than the size name, and Type K has the thickest wall, then Type L, then Type M, for any size.
Can you thread Schedule 40 PVC?
It is not recommended. Harrison Plastic says Schedule 40 walls are too thin to thread and to thread only Schedule 80 or heavier, with a 50 percent cut in the pressure rating. California’s code likewise requires at least Schedule 80 for threaded ABS joints.
What schedule is ABS drain pipe?
ABS drain, waste and vent pipe is made to Schedule 40 iron pipe sizes under ASTM D2661. Cellular core ABS pipe under ASTM F628 is also made to Schedule 40 sizes. Drain pipe flows by gravity, so it is not rated like pressure pipe.
Sources
- Harrison Plastic, Schedule 40/80 PVC Pipe and Fitting Specifications (manufacturer spec; copy hosted by InspectApedia), retrieved .
- ASTM D1785, Standard Specification for PVC Plastic Pipe, Schedules 40, 80, and 120 (scope, ASTM store), retrieved .
- ASTM D2661, ABS Schedule 40 Plastic Drain, Waste, and Vent Pipe and Fittings (scope, ASTM store), retrieved .
- ASME B36.10M, wrought steel pipe dimensions standard (description page, ASME), retrieved .
- Copper Development Association, Copper Tube Handbook (CDA Publication A4015-26/24), retrieved .
- California Plumbing Code, 2025 edition, §705.1 ABS Pipe and Joints, incl. §705.1.3 Threaded Joints (GoCodebook public copy), retrieved .
Expert review
Written by the HyrePlumber Research team. Not yet reviewed by an outside expert. We say so rather than imply a review that has not happened; see our editorial policy.
How the numbers were checked: Dimensions, pressure ratings, temperature derating and threading guidance are from one manufacturer’s published PVC spec (Harrison Plastic), labeled as such; the 120°F row in the example is our arithmetic from its factors.
Scope of PVC and ABS schedules is from ASTM D1785 and D2661 summaries; steel pipe sizing from ASME’s B36.10M description; copper wall types from the Copper Development Association handbook. The threading rule is from the 2025 California Plumbing Code (re-read 2026-10-13, unchanged from 2022).
Harrison’s Schedule 40 and 80 tables and derating factors were re-read from the PDF text on 2026-10-13. Steel pipe wall values and PEX SDR figures were not loaded and are not given. No prices are given.
Suggest a correction. We fix errors and say what changed.