Drain, stack and vent pipe sizes from drainage fixture units, plus trap arms, cleanouts and cost.
Estimates are planning aids, not a professional quote. Double-check quantities and product coverage — and any local code or permit requirements — before you buy.
⚠ Almost every jurisdiction requires a permit and a rough-in inspection — usually a water or air pressure test with every opening plugged — before any of this can be covered by drywall, insulation or a slab pour.
⚠ 3 water closets is what sizes this stack to 4", not the 20 DFU load — a 3" stack carries 48 DFU and would swallow this house easily. The binding rule is the water-closet cap: the UPC allows two on a 3" branch, and the IPC allows only two where the closets are rated 3.5 gpf or more but permits more with modern 1.28–1.6 gpf fixtures. So if you're in an IPC jurisdiction installing low-flow toilets, or your bathrooms don't actually share one vertical stack, a plumber may well be able to run 3" here — worth asking before you buy the larger pipe, since it's the biggest line on this list.
| Plumbing & Heating | $383–$518 |
| Connectors & Brackets | $121–$163 |
| Fasteners & Hardware | $24–$32 |
| Roofing | $19–$25 |
| Total | $546–$738 |
Excludes tools, delivery, tax and permit fees. Labor not included — this is a DIY materials estimate.
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About this calculator
Enter the bathrooms, kitchen sinks and laundry hookup a house needs and the DWV Rough-In Calculator sizes the drain-waste-vent system the way a plumber actually specs one: every fixture is converted to drainage fixture units (DFU), and that total is run through the same horizontal-branch-and-stack capacity table the code uses to pick a 1-1/2", 2", 3" or 4" main stack — not a guess based on room count.
It also checks the one rule DIYers get wrong most often — how far a fixture's trap can sit from its vent connection before the trap arm is too long to pass inspection — and prices out the branch pipe, individual vents, closet flanges, P-traps, cleanouts and roof flashing that go with it in either ABS or PVC. Open advanced options to set your actual run lengths, stack height and climate.
Step by step
A step-by-step walkthrough to go with your plan above. Follow the product instructions and any local code or permit requirements as you work.
List every drain, water closet and vent connection the house needs and run it through the calculator to get stack diameter, branch sizes and fitting counts before you buy anything.
Run the stack vertically from the lowest branch connection up through the roof in one continuous diameter, keeping it as close to plumb and as centrally located to the fixture groups as framing allows.
Tie the toilet's 3" branch into the stack with a sanitary wye, holding 1/4" per foot of fall, and set the closet flange at the finished floor height before anything else in that bay is closed up.
Connect lavatories, the kitchen sink, the washer standpipe and any floor drains with sanitary tees, keeping every trap arm within its code-allowed distance to its vent connection.
Run a vent riser from each fixture's branch tee up into the vent system, connecting back into the main stack above the highest fixture's drain connection.
Set one at the base of the stack and one at the upstream end of every branch, in a location that stays accessible after the walls and floors are finished.
Strap horizontal pipe at least every 4 ft and clamp the vertical stack at each floor level so nothing sags or pulls a joint apart once the system is loaded with water.
Cap or plug every open end, bring the system up to the water or air pressure your code requires, and hold it for the inspection window before any of it gets covered.
Equip the job
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Interior & Finishing
Answers
Every fixture is assigned a drainage fixture unit (DFU) value — a toilet is 3, a lavatory is 1, a tub/shower, kitchen sink, washer standpipe or floor drain are each 2 — and the total is checked against the code's capacity table for horizontal branches and stacks. As a stack, that table allows 4 DFU on 1-1/2", 10 on 2", 48 on 3" and 240 on 4". For a single-family house the DFU total almost never decides anything: a 2.5-bath home runs about 20 DFU, well inside a 3" stack. What actually picks the size is the toilet — its fixed 3" minimum trap rules out anything smaller, and a separate code cap on how many toilets one 3" branch may serve is what pushes a larger house to 4".
The trap arm is the horizontal run of drain pipe from a fixture's trap to the point it connects to a vent, and code caps how long that run can be before the trap loses its ability to hold water and reliably seal against sewer gas. The limit is tied to the pipe's diameter, and the two model codes differ more here than almost anywhere else: the UPC allows 30 in on a 1-1/4" lavatory arm and 6 ft on a 3" toilet arm, while the IPC allows 5 ft and 12 ft for the same two and exempts toilets from a maximum entirely. This page checks against the tighter UPC figures so a passing layout works under either. It's one of the most common rough-in inspection failures regardless of code, because it's easy to route a sink drain the same long distance you'd route a toilet without realizing the sink's allowance is a fraction as long.
This calculator assumes yes, which is the conservative, easiest-to-inspect approach and what it prices by default — a short vent riser from each fixture's branch up into the vent system. In practice, many codes allow wet venting, where one fixture's drain pipe is also used to vent another fixture within a limited distance, which can cut down the vent pipe and fittings a real installation needs. That's a layout decision worth making with a plumber once the walls are open, not something to guess at the planning stage.
Both are code-approved in most jurisdictions and perform the same job — the real difference is installation. ABS solvent-welds in one step with just cement; PVC needs a primer pass first (usually required to be the purple, visually-inspectable formula) before the cement goes on, which is an extra step at every joint. Regional availability and local code amendments can rule one out entirely — some jurisdictions restrict ABS below a slab or above grade — so confirm which your inspector accepts before you buy pipe.
At minimum, one at the base of the main stack where it turns horizontal, plus one at the upstream (highest) end of every horizontal branch serving a fixture group — a bathroom, the kitchen, the laundry standpipe. This calculator counts one cleanout per fixture group's branch on top of the mandatory base-of-stack cleanout. Cleanouts have to be accessible after the walls close, so plan their location before you frame anything over them.
Solvent-welding ABS or PVC is genuinely learnable, and many owner-builders do their own DWV rough-in. The part that trips people up isn't the gluing — it's holding 1/4" per foot of fall on every horizontal run, getting stack and vent sizing right, and passing the water or air pressure test with an inspector present before anything gets covered. Most jurisdictions require a permit and that inspection regardless of who does the work, so budget for it either way.