🔧Plumbing Calculator PRO
WSFU per IPC · Drain & vent sizing · Water heater · Material breakdown
Pipe Schematic — updates as you type
Supply and drain runs. Fixture units size the pipes; length and fittings drive material cost.
1 Rooms & Fixtures
2WSFU Summary (IPC Table E103.3)
| Fixture | Cold WSFU | Hot WSFU | Total Qty | DFU |
|---|---|---|---|---|
| Totals |
3 Supply Pipe Sizing
4 Drain & Vent Sizing
5 Water Heater Sizing
6 Pipe Lengths & Insulation
7 Material Breakdown
| Category | Item | Qty / Length | Unit Price | Subtotal |
|---|---|---|---|---|
8 Pricing & Labour
Labour
Results
Supply System
Drain System
Fixtures
Cost Breakdown
⚠️ Pre-Export Checklist
- All rooms and fixtures counted correctly
- Pipe lengths measured on-site
- Local plumbing code verified (IPC / UPC)
- Water pressure tested at source
- Drain slope confirmed (¼" per foot)
- Water heater type and capacity selected
- Insulation requirements reviewed
- Material prices confirmed with supplier
Plumbing Sizing Reference Guide
📐 WSFU Formulas & IPC Reference ▼
WSFU Values (IPC Table E103.3)
Cold WSFU — Bathroom group (1.0), Kitchen sink (1.0), Clothes washer (2.0), Hose bib (2.5)
Hot WSFU — Kitchen sink (1.0), Clothes washer (1.0), Dishwasher (1.0)
DFU — Toilet (3), Sink (2), Shower (2), Bathtub (3), Washer (3), Dishwasher (2), Hose bib (1)
Main Supply Sizing Formula
Supply size = f(total WSFU, supply pressure)
At 45 psi: ≤8 WSFU = ¾", 9–20 WSFU = 1", 21–48 WSFU = 1¼", 49–135 WSFU = 1½"
Drain Pipe Sizing (IPC Table 709.1)
Drain size = f(total DFU)
≤3 DFU = 2", 4–36 DFU = 3", 37–216 DFU = 4"
Vent Sizing (IPC Table 916.1)
Vent pipe must be ≥ ½ the drain size or 1½" minimum. Most residential vents: 2"–3"
🔥 Water Heater Sizing Worked Example ▼
Example: 2-bathroom house
Fixtures: 2 toilets, 3 sinks, 2 showers, 1 tub, 1 washer, 1 dishwasher
- Peak demand = 3 showers × 2.5 GPM + 1 sink × 2 GPM = 9.5 GPM simultaneous
- Tank Size = (showers × 20 gal) + (sinks × 4 gal) + (washer × 15 gal) = 71 gal → 80 gallon tank
- BTU = 80 gal × 8.33 lb/gal × (120°F − 50°F) × 1.2 safety ÷ 1 hr = 56,000 BTU/hr
- Recovery rate = 56,000 ÷ (8.33 × 70°F rise × 1 hr) = 96 GPH
Tankless Alternative
For 3 simultaneous fixtures at 7.5 GPM with 70°F rise:
BTU = 7.5 × 8.33 × 70 × 1.2 = 5,248 BTU/min →~200,000 BTU tankless unit
❌ Common Mistakes to Avoid ▼
- Ignoring peak demand — sizing only for normal use fails when guests run multiple fixtures
- Wrong drain slope — too steep causes solids to settle; too flat causes standing water. Always ¼" per foot for pipes ≤3"
- Omitting vent sizing — undersized vents cause gurgling and sewer gas entry
- No shutoff valves — every fixture needs a local shutoff for maintenance
- Pipe material mismatch — never mix copper and galvanized (dielectric corrosion)
- Neglecting expansion tanks — required on closed-loop systems with water heaters
- Not insulating hot pipes — wastes energy and increases wait time for hot water
💡 Pro Tips ▼
- PEX is faster, cheaper, and more flexible for residential supply lines; copper is preferred for commercial
- Run pipes through framing before drywall to minimize visible pipe runs
- Use manifold systems (home run) with PEX for easier future maintenance
- Support horizontal runs every 4–6 ft for supply, every 4 ft for drain (per code)
- Insulate all hot water pipes with R-3 foam — saves 3–5% on energy bills
- Label all shutoff valves during install — future you will be grateful
- Test with pressure gauge before closing walls — 60 psi for 15 min, max 1 psi drop
- Photograph rough-ins before closing walls for insurance and future reference
Plumbing — 3D Preview
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حاسبات مرتبطة
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Adjustments (applies to exports)
Contingency is added as a separate line on the exported cost summary. Waste % is printed as an advisory reminder.
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| Item | Pinned | Current | Change |
|---|---|---|---|
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✅Method, Sources & Review
Maintained by theBuildingCalc methods desk· Last reviewedSeptember 23, 2026. This calculator implements the standards and references below; every figure can be rechecked against the formulas and worked example on this page.
Results are estimates, not engineering advice. Verify against local codes and licensed professionals for structural, electrical, and gas work. See ourTerms. Spotted an error? Report it— corrections ship with the next review.