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3-Piece Bathroom Rough-In Estimator

Estimate supply lines, drain pipes, and fittings for a standard toilet, sink, and shower rough-in using IPC pipe sizing rules.

Fixture Distances

Enter distance from the main soil stack or manifold to each fixture.

Supply Lines (1/2")

75 ft
Total Length (Inc. 20% Routing Waste)
Toilet Drain (3" or 4" PVC)8 ft
Vanity/Shower (1.5" or 2" PVC)27 ft
1/2" Hot Water (PEX)32.4 ft
1/2" Cold Water (PEX)42 ft

Estimated Fittings

Sanitary Tees3
90° Elbows12
Angle Stop Valves3
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What is 3-Piece Bathroom Rough-In: IPC Pipe Sizing and Supply Layout?

A standard 3-piece bathroom (toilet, vanity sink, shower/tub) requires different pipe sizes for each fixture based on Drain Fixture Units (DFU) assigned by the International Plumbing Code (IPC). The supply side uses either copper or PEX in ½-inch minimum diameter to each fixture. This estimator calculates material take-off quantities — pipe lengths, fitting counts, and stub-out materials — based on the distance from your main stack or manifold to each fixture location.

Mathematical Foundation

IPC Drain Fixture Units (DFU) & Minimum Pipe Sizing
Toilet: min. 3\" drain. Vanity: 1.5\". Shower: 2\". Stack: 3\" or 4\"
Toilet(WC)Toilet (WC)= Assigned 3–6 DFU depending on flush volume. IPC Table 709.1 requires minimum 3-inch drain from the toilet flange to the stack. Most jurisdictions require 4-inch underground.
Lavatory(Vanity)Lavatory (Vanity)= Assigned 1–2 DFU. Minimum 1.5-inch P-trap and drain arm; 1.25-inch drain stopper assembly. P-trap must be within 24 inches of the vent.
Shower/TubShower/Tub= Assigned 2 DFU for a single shower. Minimum 2-inch drain and trap. Combined shower/tub counts as 3 DFU in some jurisdictions.
Supply Line Routing Buffer (20% Factor)
Lpipe=Ldirect×1.20L_{pipe} = L_{direct} \times 1.20
LpipeL_pipe= Actual pipe length to order (linear feet)
LdirectL_direct= Straight-line distance from manifold or stack to fixture stub-out
1.201.20= 20% routing factor — accounts for joist penetrations, stud bay routing, vertical drops, and horizontal offsets to properly locate stub-outs

Laws & Principles

  • Hot vs. Cold Supply Routing: Cold water runs to all three fixtures (toilet tank, vanity, and shower). Hot water runs to only two (vanity and shower/tub) — toilets use cold water only. Factor this into supply pipe runs: your cold supply trunk is longer than hot. In a manifold (home run) system, each fixture gets its own dedicated line from the manifold.
  • PEX vs. Copper Trade-Off: PEX (A or B) is flexible and can sweep around corners at gentle radius bends without fittings, reducing fitting count by 30–50% vs. copper on a typical bath rough-in. Copper requires hard 90° elbows (sweated) at every direction change. PEX costs approximately 30–50% less per linear foot than copper but requires crimp/clamp fittings at stub-outs and manifold connections. Use copper in exposed locations (above ground, visible) and where local code requires it.
  • Drain Venting Requirements: IPC requires every fixture trap to be vented within a maximum developed length from the trap weir: lavatory = 5 ft (1.5-inch pipe); shower = 6 ft (2-inch); toilet = 6 ft (3-inch). A wet-vent arrangement — where one fixture's drain also serves as the vent pipe for nearby fixtures — reduces vent pipe labor but must be sized for both drain and vent DFU simultaneously. This estimator assumes a standard wet-vent configuration for compact bathrooms.

Step-by-Step Example Walkthrough

" Roughing in a bathroom where the toilet is 8 ft from the stack, vanity is 12 ft, and shower is 15 ft from the stack. "

  1. Toilet drain: 8 ft of 3-inch PVC (or ABS) from flange to stack connection. Add a 3×3×3 wye at the stack.
  2. Vanity drain: 12 ft of 1.5-inch PVC to the P-trap stub-out. Add 1.5-inch P-trap, cleanout, and vent tie-in.
  3. Shower drain: 15 ft of 2-inch PVC to 2-inch P-trap (built into shower pan). Add 2-inch cleanout fitting.
  4. Cold supply (all 3 fixtures): (8 + 12 + 15) × 1.20 routing factor = 42 ft of ½-inch PEX or ½-inch Type M copper.
  5. Hot supply (vanity + shower only): (12 + 15) × 1.20 = 32.4 ft of ½-inch hot supply.
Final Result: Material list: 8 ft of 3-inch PVC, 12 ft of 1.5-inch PVC, 15 ft of 2-inch PVC, 42 ft of cold ½-inch PEX, 32.4 ft of hot ½-inch PEX, plus associated P-traps, wye fittings, and cleanouts. Add 10% overage for waste and cuts.

Quick Answer: What pipe sizes do I need for a 3-piece bathroom rough-in?

Per the International Plumbing Code (IPC), a standard 3-piece bathroom rough-in requires: Toilet drain: 3″ minimum (4″ underground in most jurisdictions); Vanity drain: 1.5″ with a P-trap within 24″ of the vent; Shower drain: 2″ with integral P-trap at the shower base. Supply lines to all three fixtures use ½″ minimum (copper or PEX) with separate hot and cold runs — cold goes to all three fixtures; hot goes only to the vanity and shower. The 20% routing factor (L × 1.2) accounts for the real-world path of pipe through joists, stud bays, and vertical drops when calculating material quantities from your manifest distances to each fixture.

Bathroom Rough-In Pipe Sizing Reference (IPC)

Fixture Drain Size (IPC Min.) Supply (Hot/Cold) Rough-In Dimension
Toilet (WC) 3″ (4″ underground) ½″ cold only (toilet fill valve) Flange center: 12″ from finished wall (standard); 10″ or 14″ for non-standard. Cold stub-out: 6″ left of flange, 6″ above floor (IPC R308.3)
Vanity / Lavatory 1.5″ drain arm ½″ hot + ½″ cold Drain center: 17″–19″ above subfloor (for standard 8″ offset connection). Supplies: 21″ AFF, 4″ apart centered on drain
Shower (stand-alone) 2″ integral P-trap ½″ hot + ½″ cold (or ¾″ to shower valve) Drain center: per shower pan layout. Valve stub-outs: 48″–60″ AFF, 6″ apart. Showerhead: 72″–80″ AFF
Tub/Shower Combo 1.5″ or 2″ drain ½″ hot + ½″ cold (or ¾″ to mixing valve) Drain offset from wall: per tub model (typically 15″–16″ from head wall). Valve stub-outs: 28″–32″ AFF; spout: 14″–18″ AFF
AFF = Above Finished Floor. All supply heights are finished floor reference — add subfloor thickness if measuring from subfloor during rough-in (typically 0.75″–1.25″ for ¾″ plywood). Verify with fixture manufacturer rough-in sheet before cutting supply locations. IPC minimums; local amendments may require larger pipe sizes. Underground drain outside the building footprint typically requires 4″ minimum per UPC.

Pro Tips & Rough-In Mistakes

Do This

  • ✓Confirm the toilet's rough-in dimension before cutting the closet flange location — most toilets are 12″, but 10″ and 14″ rough-ins exist. The rough-in dimension is measured from the finished wall surface (not the framing) to the center of the toilet flange. A 12″ toilet on a 10″ rough-in won't fit; a 10″ toilet on a 12″ rough-in will leave a visible gap behind the toilet. Always pull the toilet's spec sheet before cutting. For new construction, set the flange at 12″ from the face of the wall framing + the finished wall thickness (tile + backer + drywall = typically 1″–1.5″ total, so set the flange at 13″–13.5″ from the stud face).
  • ✓Set drain stub-outs to the rough height before closing walls, then cut to final height after flooring is installed. A common rookie mistake is cutting drain arms to finished height during rough-in before tile/hardwood flooring is installed. Flooring adds 0.5″–1.5″ of height — your supply stub-outs and drain arms will be at the wrong height post-flooring. Rough-in stub-outs approximately 2″ above final estimated finished floor height, then trim to exact specification after all flooring is complete and before setting fixtures.

Avoid This

  • ✗Don't run the toilet drain pipe with insufficient slope — IPC requires ¼″ drop per foot (2% grade) for 3-inch drain pipes. Insufficient slope (<1⁄8″/ft) allows solids to settle in the pipe and create chronic clogs. Excessive slope (>1⁄2″/ft) causes liquids to run ahead of solids (called “self-scouring” failure) — leaving waste behind. The IPC minimum is ¼″ per foot for pipes 3″ and smaller. On a 12-foot toilet drain run, total drop should be 3 inches from the flange to the stack connection. If your floor framing doesn't allow this grade to the stack, you may need a pressure-assist toilet or a sewage ejector pump (macerator) if the drain must run uphill.
  • ✗Don't connect the P-trap to the drain arm at any distance beyond the IPC maximum trap-to-vent distance. IPC Table 909.1 limits the maximum distance between a fixture trap's weir and the vent connection: lavatory = 5 feet (with 1.5″ pipe); shower = 6 feet (with 2″ pipe); toilet = 6 feet (with 3″ pipe). Exceeding this distance creates siphoning: when the trap drains, negative pressure pulls water out of the P-trap, breaking the seal and allowing sewer gases (including hydrogen sulfide and methane) to enter the occupied space. The solution is either relocating the vent tie-in closer to the fixture, or using an air admittance valve (AAV) — permitted in most jurisdictions for single fixtures in remote locations.

Frequently Asked Questions

Should I use PEX or copper for bathroom supply lines?

Both are code-compliant; the choice depends on cost, skill, and local conditions. PEX advantages: flexible (fewer fittings), faster to install (crimp or clamp with inexpensive tools), 30–50% cheaper per foot than copper, freeze-resistant (expands rather than splits on freezing), corrosion-resistant in aggressive water chemistry. Copper advantages: rigid (easier to maintain exact stub-out locations), estimated 50+ year service life when properly installed, traditional code acceptance everywhere, no potential for rodent damage (PEX can be gnawed), better performance in high-UV exposure locations. PEX-A (expansion) is the premium type but requires an expansion tool; PEX-B (crimp) is most common. For concealed rough-in work, PEX is generally preferred by speed-focused plumbers. For visible or exterior locations, copper or CPVC is typical. Always verify with your local AHJ (Authority Having Jurisdiction) — a small number of municipalities still restrict PEX for domestic water.

What is the standard toilet rough-in distance?

The standard rough-in is 12 inches from the finished wall to the center of the toilet flange. This is the most common specification, used by the vast majority of residential toilets sold in North America. However, 10-inch and 14-inch rough-ins exist for renovation work where the existing drain cannot be relocated. When buying a toilet for an existing rough-in: measure the distance from the finished wall to the center of the floor bolts (or to the existing flange center if the toilet is removed). Buy a toilet with that matching rough-in dimension. Note that IBC accessibility requirements (ADA) for commercial bathrooms require 18 inches of centerline clearance from a side wall and 60 inches of clearance from the opposite wall — this affects rough-in location when designing accessible bathrooms.

How deep should bathroom rough-in pipes be set below the slab?

For slab-on-grade construction, underground drain pipes are typically set 12–18 inches below the slab surface to allow for pipe slope, fittings, and concrete coverage above the pipe. The toilet flange sits at or slightly above the finished floor level — the drain pipe from the flange drops to the underground run at the required ¼″/ft slope. IPC requires minimum 2 inches of concrete cover over drain pipes in slabs. For a typical 3-inch toilet line running 10 feet before joining the main 4-inch line, the pipe drops 2.5 inches over the run (10 ft × ¼″/ft), plus fitting depths. The toilet flange must be set at the correct height relative to the finished floor: top of flange should be flush with or up to ¼″ above the finished floor surface — use a flange extender if the finished tile is thicker than anticipated. Getting this wrong requires slab-jack cutting to correct, which is expensive.

Do I need a permit for a bathroom rough-in?

Yes — virtually all new bathroom rough-in work requires a plumbing permit and inspections at multiple stages. Typical inspection stages: (1) Underground rough-in: before the concrete slab is poured (for slab construction); (2) Above-ground rough-in: after all supply and drain pipes are installed and pressure-tested, but before walls are closed; (3) Final inspection: after all fixtures are set, connected, and functional. Rough-in inspection typically requires a pressure test: supply lines at 80–100 PSI for 15 minutes with no drop; drain pipes filled with water (test plug at the lowest point) for a timed leak check. Working without a permit creates homeowner liability, insurance coverage issues, and potential sale-blocking title defects. In most states, a licensed plumber is required to pull the permit and perform the rough-in work (though homeowners may be permitted to perform work on their own primary residence in some jurisdictions).

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