Free Plumbing Calculators
Free plumbing calculators for pipe sizing, flow rate, drainage slope, hot water tanks, and gas lines. Instant code-aware estimates for plumbers and DIY.
14 free calculators · No account required
Pipe Sizing & Pressure Drop Calculator
Calculate pipe velocity and pressure drop using Hazen–Williams for PEX, Copper, and PVC.
- Velocity and pressure drop from GPM and pipe length
- PEX, Copper Type L, and PVC Sch 40 lookup tables
Water Flow Rate Calculator (PSI → GPM)
Convert water pressure (PSI) into volumetric flow rate (GPM) instantly based on pipe size and connection types.
- PSI to GPM using Bernoulli discharge formula
- Standard pipe inside diameter lookup (1/2" to 1-1/2")
Hot Water Tank Sizing Calculator
Calculate the ideal residential hot water tank capacity (First Hour Rating) based on occupants, simultaneous fixtures, and energy source.
- First Hour Rating / peak demand sizing method
- Occupant, shower, and appliance concurrent load inputs
Drainage Slope Calculator (Code-Compliant)
Calculate minimum drainage pipe slope and total fall based on UPC/IPC plumbing code thresholds.
- IPC/UPC minimum slope lookup by pipe diameter
- Total fall calculation from run length and slope
Copper Pipe Expansion Calculator
Calculate the thermal linear expansion of copper pipes and determine the required expansion loop leg length and support interval movement.
- CDA linear expansion coefficient (9.3 × 10⁻⁶ in/in/°F)
- Standard Type K/L/M outside diameter lookup (1/2" to 2")
Water Hammer Pressure Calculator
Calculate transient shockwave surge pressure from water hammer using the Joukowsky equation based on pipe material, GPM, and valve closing speed.
- Joukowsky surge equation with material wave speed lookup
- Fluid velocity from GPM and inner pipe diameter
Irrigation Zone Flow Calculator
Calculate total irrigation zone flow rates across custom spray heads, rotors, and drip loops to match valve and main line capacities.
- Spray, rotor, and drip emitter GPM summing engine
- Valve size safe flow defaults with optional supply override
Well Pump Sizing Calculator
Calculate required well pump flow rate (GPM), Total Dynamic Head (TDH), and motor horsepower to size commercial submersible or jet pumps.
- AWWA fixture and bedroom minimum GPM baselines
- TDH from vertical lift, pressure head, and pipe friction
Sump Pump Capacity Calculator
Calculate required sump pump sizing, pit volume capacity, and total dynamic head to ensure reliable basement flood protection.
- Live inflow test or basement area estimation modes
- Pit volume geometry with safety multiplier profiles
PEX Bend Radius Calculator
Calculate minimum allowable bend radius for PEX-A, PEX-B, and PEX-C tubing under various thermal states to prevent permanent plumbing wall kinking.
- CTS outside diameter lookup (3/8" to 1") with ASTM F876 bend multipliers
- PEX-A, PEX-B, and PEX-C cross-linking class selection
Gas Pipe Sizing Calculator (BTU Load + Equivalent Length)
Size residential or commercial gas lines using the International Fuel Gas Code sizing parameters based on multi-appliance BTU loads and equivalent fitting lengths.
- IFGC Table 402.4(1) black iron capacity lookup at 0.5 in. w.c.
- Multi-appliance BTU load summation with add/remove rows
Fixture Unit (DFU) to GPM Converter
Convert plumbing fixture units (DFU/WSFU) to fluid design velocities in GPM utilizing piece-wise IPC and UPC Hunter's Curve regressions.
- Piece-wise IPC and UPC Hunter's Curve interpolation engine
- Multi-appliance fixture matrix with editable DFU and quantity rows
Rainwater Harvesting & Gutter Flow Calculator
Calculate total rainwater harvesting potential in gallons alongside peak storm runoff velocities in GPM to specify IPC code-compliant gutter and downspout sizes.
- Roof catchment runoff GPM from regional design storm intensity
- Rainwater harvest volume from storm accumulation depth
Thermal Expansion Tank Sizing Calculator
Calculate required water heater expansion tank sizes and fluid acceptance volume parameters utilizing temperature swing density dynamics and Boyle's Law.
- Volumetric water thermal expansion from cold supply to setpoint
- Boyle's Law acceptance factor from pre-charge and relief pressures
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