Plumbing Calculators
Drain Slope Calculator
Calculate required drain pipe slope and total fall over a run length using standard plumbing code minimums that vary by pipe diameter.
Drain Vent Pipe Size Calculator
Find a reference recommended drain vent pipe diameter based on total drain fixture units (DFU) in a plumbing system.
Dripping Faucet Water Waste Calculator
Calculate how many gallons of water a dripping faucet wastes per day and per year based on drip frequency.
Faucet Flow Rate Calculator
Calculate your faucet's actual flow rate in gallons per minute using a simple container-and-timer test.
Grease Trap Sizing Calculator
Estimate a recommended grease trap size for a commercial kitchen based on meals served per day and wastewater flow.
Hot Water Wait Time Calculator
Calculate how long you'll wait for hot water to arrive at a fixture based on pipe length, diameter, and flow rate.
PEX Pipe Thermal Expansion Calculator
Calculate how much a run of PEX pipe will expand based on its length and the expected temperature change.
Pipe Flow Calculator
Calculate flow rate in GPM from pipe diameter and water velocity using the continuity equation, with a reference table of capacity by common pipe sizes.
Pipe Insulation Thickness Calculator
Calculate recommended pipe insulation thickness based on pipe diameter and your local climate zone.
Pipe Pressure Drop Calculator
Calculate friction pressure drop through a pipe using the Hazen-Williams equation, with C-factors for PVC, copper, and cast iron or steel pipe.
Pipe Size Calculator
Determine the minimum pipe diameter needed to deliver a required flow rate without exceeding a target maximum velocity, to prevent noise and water hammer.
Pipe Volume Calculator
Calculate the water volume held inside a pipe from its diameter and length, in gallons or liters, using either imperial or metric unit inputs.
Septic Tank Size Calculator
Look up the standard minimum septic tank capacity by bedroom count, based on common state and IAPMO/UPC plumbing code sizing tables for new systems.
Sump Pump Sizing Calculator
Convert a basin fill-rate test into groundwater inflow rate and a recommended sump pump horsepower tier for accurate, property-specific sizing.
Toilet Water Usage Calculator
Calculate daily and annual water usage from toilet flushing based on gallons per flush and household size.
Water Heater Recovery Time Calculator
Calculate how long it takes a water heater to fully recover (reheat) after being depleted, based on tank capacity and recovery rate.
Water Heater Size Calculator
Find the recommended storage water heater tank capacity for a household based on standard sizing guidance by number of occupants and usage patterns.
Water Pressure Calculator
Convert between water column height and static pressure in either direction using the standard 0.433 psi per foot hydrostatic constant for water.
Water Softener Salt Usage Calculator
Calculate how many pounds of salt your water softener uses per month based on water hardness and daily usage.
Water Tank Size Calculator
Size a storage or cistern tank from household size, daily per-person water use, and required storage reserve days for wells and off-grid systems.
Water Has to Go Somewhere, Correctly
Plumbing systems depend on getting pipe size, pressure, and slope right — too small a pipe restricts flow, too little slope on a drain lets waste settle instead of flowing out. These ten calculators cover pipe sizing and water system math.
Water Heater Size by Household
| Household Size | Typical Tank Size |
|---|---|
| 1-2 people | ~30-40 gallons |
| 3-4 people | ~40-50 gallons |
| 5+ people | ~50-80 gallons |
Peak usage patterns matter as much as headcount — a household that runs the dishwasher, washing machine, and a shower back-to-back needs more capacity (or a tankless system) than the same size household with more staggered usage. Size your own with the Water Heater Size Calculator.
Popular Plumbing Calculators
- Pipe Size Calculator — determines minimum pipe diameter needed for a target flow rate.
- Drain Slope Calculator — checks whether a drain line's slope meets the standard 1/4 inch per foot guideline.
- Septic Tank Size Calculator — estimates required septic tank capacity from household size and usage.
Related: HVAC Calculators, Construction Calculators.