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Plumbing

What it's for

A rough-in takeoff from a fixture count. Set how many of each fixture the house has and you get the total drainage fixture units, a main drain size, a fittings estimate, a riser drawing, and a material list of drain, stack, supply and vent pipe. It is an estimate for pricing and ordering. One line on the results card passes or fails: the main supply size. It does not lay out or size the branches.

Step by step

The example is the screen as it opens: one of each fixture, two hose bibbs, two stories, 60' 0" from the main to the farthest fixture, a 1 main supply and 40–49 psi.

Plumbing inputs: FIXTURES with TOILET 1, BATHROOM SINK 1, KITCHEN SINK 1, BATHTUB 1, SHOWER 1, WASHER 1, DISHWASHER 1, UTILITY SINK 1 and HOSE BIBB 2, then STORIES 2, MAIN TO FARTHEST FIXTURE 60' 0" and MAIN SUPPLY SIZE 1, with WATER PRESSURE and WASTE FACTOR below the fold. The answer bar reads 16 DFU, a green 1" main supply carries 16.3 w.s.f.u. at 72' 0" developed (IRC Table AP201.1, 40–49 psi), and 3 in main drain. 1 2 3 4
Steps 1–4. Step 1 is the whole FIXTURES list, one − + row per fixture.
  1. Under FIXTURES, set the count of each with − and +: TOILET, BATHROOM SINK, KITCHEN SINK, BATHTUB, SHOWER, WASHER, DISHWASHER, UTILITY SINK and HOSE BIBB. The list is fixed. Set a fixture to 0 if the job has none.
  2. STORIES — how many floors have plumbing. It multiplies the supply pipe run and nothing else. The example is 2.
  3. MAIN TO FARTHEST FIXTURE — the pipe route from where the main comes in to the fixture farthest from it, measured the way the pipe will run. The example is 60' 0".
  4. MAIN SUPPLY SIZE — 1/2, 3/4, 1, 1 1/4 or 1 1/2. It names the supply pipe row in MATERIALS, and the results card checks it against the fixtures. The example is 1.
  5. WATER PRESSURE — the lowest static pressure at the meter: 30–39, 40–49, 50–60 or over 60 psi. Ask the water utility or put a gauge on a hose bibb. Take off 0.5 psi for every foot the highest fixture sits above the meter. The example is 40–49 psi.
  6. WASTE FACTOR — extra pipe and fittings, in steps of 5%. The example is 10%.
  7. Read RESULTS: 16 DFU, 3 in main drain, 33 fittings estimated, and the green line 1" main supply carries 16.3 w.s.f.u. at 72' 0" developed (IRC Table AP201.1, 40–49 psi).
  8. Tap BASIS & WHAT WAS ASSUMED to see which code tables the fixture units and the drain size come from.
  9. Scroll down to the riser drawing.
  10. Read MATERIALS for the order.

Reading the results

Plumbing scrolled to the results: MAIN SUPPLY SIZE 1, WATER PRESSURE 40–49 psi picked among 30–39, 40–49, 50–60 and Over 60 psi, and WASTE FACTOR 10%. RESULTS reads 3 in main drain; 33 fittings estimated; Fall over 60' 0": 7-1/2" at 1/8"/ft (IRC P3005.3, IPC 704.1); 1' 3" at 1/4"/ft (UPC 708.1); and the green 1" main supply carries 16.3 w.s.f.u. at 72' 0" developed (IRC Table AP201.1, 40–49 psi), then the BASIS & WHAT WAS ASSUMED row and the link Check before you cut · Measure twice. The top of the DWV riser drawing begins under them, with VTR and 1 WC 3 DFU Σ3. The answer bar keeps 16 DFU and the green supply line, cut off at 72'…. 5 6 7 8
Steps 5–8: the pressure and the waste, then the counts and the supply check, and the basis row.
Plumbing scrolled to the end of the riser: the DWV RISER drawing shows a branch for each fixture labelled with its DFU and a running total, from 1 WC 3 DFU Σ3 down to 1 US 2 DFU Σ16, 2 HB 0 DFU · NO DWV dashed, a 3 IN drain to SEWER dimensioned 60' 0", and the notes 16 DFU · 1 WC · DRAIN 3 IN — 3 IN MIN, ANY WC; FALL 1' 3" @ 1/4"/FT UPC · 7-1/2" @ 1/8"/FT IRC/IPC; DRAIN 66 LF = MAIN→FARTHEST +10% · VENT 45 PROXY; SCHEMATIC RISER — NOT ISOMETRIC · Σ = RUNNING DFU; BRANCH ORDER NOT BY STOREY — ONLY BASE Σ ENGINE-TRUE, over the title strip DWV RISER, 16 DFU · 3 IN MAIN DRAIN, NOT TO SCALE. MATERIALS begins: Main drain 3 in — 3 in min with any WC; 4 in over 3 WCs (UPC 703.2) — verify local code, 66 lin ft; Supply pipe 1, 132 lin ft; Assorted fittings, 33 pcs; Stack pipe 3 in — ~10' a storey + 2' through the roof, 25 lin ft; and Vent pipe 2 in — rough proxy, 45 lin ft. 9 10
Steps 9 and 10: the riser drawing, then the order with waste added.

The headline is the total drainage fixture units: each fixture's count times its unit value, added up. A hose bibb has no drain, so it adds nothing. The drawing shows every fixture's value and the running total, from 1 WC 3 DFU Σ3 to 1 US 2 DFU Σ16 in the example.

The main drain line is the size picked for the building drain from the total and from how many toilets there are. The first note under the drawing says why. In the example: 16 DFU · 1 WC · DRAIN 3 IN — 3 IN MIN, ANY WC. Any toilet makes the drain at least 3 in. With no toilet, a 2 in drain carries up to 21 DFU laid at 1/4"/ft (IRC 2021 Table P3005.4.2), so the drain is 2 in up to 21 DFU and 3 in above that. A 3 in drain carries 36 DFU even at 1/8"/ft. Over 36 DFU, or with more than three toilets (the UPC's limit), it is 4 in. With no fixture that drains, the line reads supply only — no DWV and the drain and vent rows leave the material list.

Big loads. A 4 in building drain carries 180 DFU at 1/8"/ft, 216 at 1/4"/ft and 250 at 1/2"/ft (IRC 2021 Table P3005.4.2, the same as IPC Table 710.1(1)). From 181 to 216 DFU the results add a line, 4 in at 1/4"/ft min — no 1/8"/ft over 180 DFU (IRC P3005.4.2), the cut sheet adds a Drain Slope row, and the drawing prints only the 1/4"/ft fall: FALL … @ 1/4"/FT UPC/IPC — NO 1/8 OVER 180 DFU. Over 216 DFU the main drain is 5 in, with the rule OVER 216 DFU on the drawing; a 5 in drain carries that load at 1/8"/ft too (IPC Table 710.1(1)). Up to 250 DFU a 4 in drain is still allowed if it is laid at 1/2"/ft, so from 217 to 250 DFU the results and the cut sheet add Or 4 in at 1/2"/ft — carries 250 DFU (IRC P3005.4.2). Loads that big are small multifamily work, so have the drain designed.

The main supply line checks MAIN SUPPLY SIZE. It adds up the water-supply fixture units of your fixtures (IRC 2021 Table P2903.6: toilet 2.2, bathroom sink 0.7, hose bibb 2.5, the rest 1.4 each), takes your run times 1.2 for the fittings, and reads IRC Appendix AP Table AP201.1 at your WATER PRESSURE. The line is green when your size carries the load and red when it is too small, naming the size the table asks for. With a 3/4 supply the example reads 3/4" main supply too small: 16.3 w.s.f.u. at 72' 0" developed needs 1". Past the table, over 500' developed or past its largest pipe, the line turns amber and says to size the supply by engineering. Appendix AP is binding only where your jurisdiction adopts it, but the IRC asks for a supply sized from demand either way (P2903.7).

Fittings estimated is a rule of thumb, a few fittings for every fixture, with waste added. Treat it as a starting count.

BASIS & WHAT WAS ASSUMED names the IPC tables the fixture units and the drain size are taken from, and the value used for a washer standpipe. The next says every fixture is counted on its own: the tables also give group values, such as a whole bathroom group, that total less, so this total is on the safe side. Then come how the main supply is checked, that MATERIALS are the main runs only, and the trap-to-vent table. If you work to a different code, check your own table.

The drawing is a schematic riser: the stack with its vent through the roof (VTR), a branch for each fixture, and the building drain running to the sewer with your run dimensioned. The fixture tags are WC toilet, LAV bathroom sink, KS kitchen sink, TUB, SH shower, WM washer, DW dishwasher, US utility sink and HB hose bibb. With a 3 in, 4 in or 5 in drain the drawing prints the fall over your run twice, once for each model code, and labels them (with a 2 in drain both codes agree and it prints one fall, and over 180 DFU on a 4 in drain only the 1/4"/ft fall is allowed, so it prints that one): FALL 1' 3" @ 1/4"/FT UPC · 7-1/2" @ 1/8"/FT IRC/IPC in the example (the IRC's slope rule, P3005.3, is the IPC's). On a long run the note runs out of room and keeps the slope without the second fall, so the results card always gives both: Fall over 60' 0": 7-1/2" at 1/8"/ft (IRC P3005.3, IPC 704.1); 1' 3" at 1/4"/ft (UPC 708.1). The boxed inset shows a fixture's trap arm running to its vent, headed IRC TABLE P3105.1; BASIS prints that table, the longest trap arm by trap size: 1-1/4" 5', 1-1/2" 6', 2" 8', 3" 12', 4" 16'. Two notes say the riser is schematic, not isometric, and that the branches are not arranged by story. Only the total at the base is a calculated figure. Pinch to zoom, drag to move around, double-tap to reset, or tap the expand button at its top right for the whole screen. See Reading the drawing.

MATERIALS, with waste added and rounded up:

The buttons wait for your own numbers: SHARE PDF and the list icon in it stay dimmed, and a tap on SAVE only answers Enter your job's numbers first. After that SHARE PDF shares the riser, the counts, your fixtures and the materials, the list icon at the right end of the same button shares the material list alone, and SAVE puts the result in History. The PDF footer reads Estimate — verify dimensions and local code before cutting/ordering. Your local code and your inspector govern pipe sizes, slope and venting.

Plumbing is a Pro calculator. The PDF and History are Pro too. Pro is a one-time purchase. See Free and Pro.

Common mistakes