Plumbing Calculators
17 free professional-grade tools. Code-referenced plumbing calculators — UPC & IPC pipe sizing, drainage, gas
Water Supply
Water Supply Fixture Unit (WSFU) Calculator — UPC & IPC
Add up water supply fixture units (WSFU) for residential or commercial buildings. The total WSFU load feeds directly into pipe sizing via Hunter’s curve or the IAPMO/ASPE Water Demand Calculator.
Hot Water Recirculation Pump Calculator — ASPE PDH Vol. 2
Size a domestic hot water recirculation pump by loop heat loss and pipe friction. Enter loop length, heat loss per foot, temperature drop, and return-line pipe size to get required flow (gpm) and pump head (ft).
PEX Manifold Sizing Calculator — UPC 604 / ASTM F876
Size a PEX manifold feed or home-run trunk from WSFU load. Converts fixture units to gpm, selects the smallest PEX tube whose actual inside diameter keeps velocity at or below the 8 ft/s UPC 604 limit, and reports Hazen-Williams friction loss.
Water Demand Calculator — IAPMO/ASPE WDC (UPC Appendix M)
Estimate peak domestic water demand (gpm) from total WSFU using the IAPMO/ASPE Water Demand Calculator envelope (UPC Appendix M). Compares the modern WDC method to the legacy Hunter curve for pipe sizing.
Water Pressure Drop Calculator — Hazen-Williams
Calculate water pressure drop (psi) and flow velocity in copper, PEX, CPVC, PVC, or galvanized steel pipe using the Hazen-Williams equation. Enter flow, length, material, and pipe size.
Drainage & Sewage
Manning Equation Drainage Flow Calculator — Partial-Full Pipe
Calculate gravity drainage flow rate (cfs & gpm) in a partially full pipe using Manning’s equation. Enter pipe size, material, slope, and depth-of-flow ratio.
Drainage Fixture Unit (DFU) Calculator — IPC Table 709.1
Add up drainage fixture units (DFU) for residential or commercial buildings. The total DFU load feeds into horizontal drainage pipe sizing via IPC Table 710.1 / UPC Table 710.1.
Drainage Pipe Sizing Calculator — IPC Table 710.1 / UPC
Size horizontal drainage and sewer pipe by total Drainage Fixture Units (DFU) and slope. Returns the minimum pipe size per IPC Table 710.1 / UPC Table 710.1 for 1/8, 1/4, or 1/2 inch per foot slopes.
Roof Drain & Rainwater Leader Sizing Calculator — IPC 1106
Size roof drains, vertical leaders, and horizontal rainwater piping by code-tabulated roof area and rainfall intensity per IPC Table 1106.1/1106.2, UPC 1105–1108, and ASME A112.6.4.
Storm Drainage Calculator — Rational Method + Pipe Sizing
Calculate storm water runoff (cfs and gpm) by the Rational Method and size the horizontal storm drain pipe using Manning’s equation. Enter drainage area, rainfall intensity, runoff coefficient, pipe material, and slope.
Trapezoidal Channel Flow Calculator — Manning Open Channel
Calculate flow capacity (cfs) and velocity (ft/s) of a trapezoidal open channel using Manning’s equation. Enter bottom width, flow depth, side slope, channel slope, and lining material.
Gas & Hot Water
Natural Gas Pipe Sizing Calculator — UPC 1208.4 / IPC 402.4
Size natural-gas piping (Schedule 40 steel) by the UPC Table 1208.4.1 longest-run method. Enter the total connected CFH load and longest run to get the minimum pipe size at 0.5 psi inlet pressure.
Pipe Friction & Equivalent Length Calculator — Crane TP-410
Sum the equivalent length (L/D method) of valves and fittings on a pressurized water line and compute the total Hazen-Williams friction loss. Based on Crane Technical Paper 410 and ASPE PEDH Vol. 2.
Pipe Thermal Expansion Calculator — ΔL = α·L·ΔT
Calculate linear thermal expansion (inches) and restrained-pipe stress (psi) for copper, steel, PEX, CPVC, and PVC. Enter pipe length and temperature change to size expansion offsets and expansion loops.
Water Heater Sizing Calculator — First Hour Rating (FHR)
Size a storage water heater by ASHRAE First Hour Rating. Enter tank volume, BTU input, and recovery efficiency, then compare the result to peak-hour hot water demand for showers, dishwasher, and laundry.
Wastewater & Pumps
Septic Tank Sizing Calculator — EPA 40 CFR 503 / UPC 725
Estimate minimum septic tank capacity by bedroom count per the EPA / UPC / HUD baseline formula. Includes daily wastewater flow estimate and 2-day detention volume for solids settling. Always verify with local health department rules.
Sump Pump Sizing Calculator — Total Dynamic Head & HP
Size a sump or sewage ejector pump by inflow (gpm), static lift, and discharge pipe friction. Returns Total Dynamic Head (TDH), flow velocity, and estimated motor horsepower per IPC 912 and Crane TP-410.