Interior plumbing cost & sizing calculators
Free, no-signup interior-plumbing calculators for homeowners, DIYers and buyers — water-heater sizing & cost, water-supply pipe sizing, drain / waste / vent sizing, fixtures & water use, gas piping & appliance load, and whole plumbing-project cost. Every tool works on the prices you enter and shows its formula, a worked example and a reference table.
Water Heater — Sizing & Cost
The traffic anchor: size a tank by peak-hour demand or first-hour rating, size a tankless unit from GPM and temperature rise, work out recovery rate, estimate installation cost, compare tank vs tankless, check heat-pump savings and size a thermal-expansion tank.
All Water Heater — Sizing & Cost tools →Water Supply & Pipe Sizing
The technical long-tail: supply pipe size from fixture units, water pressure and elevation head, friction / pressure loss, water volume in the pipe and time-to-hot, a bucket-test flow rate, and peak demand from WSFU.
All Water Supply & Pipe Sizing tools →Drain, Waste & Vent
Interior drainage only: total drainage fixture units, drain pipe size from DFU, drain slope and fall, vent pipe size, trap-arm length, and drain cleaning / snaking / hydro-jet cost.
All Drain, Waste & Vent tools →Fixtures & Water Use
Everyday water: daily household water use, old vs low-flow toilet savings, faucet / shower aerator savings, the cost per shower, water-supply fixture units, and how much a dripping faucet or running toilet wastes.
All Fixtures & Water Use tools →Gas Piping & Appliance Load
Gas math for planning only: total appliance gas load in BTU/hr, gas pipe size from BTU and run length, BTU ↔ CFH conversion, a gas line run cost, and capacity vs allowable pressure drop. Gas work is licensed-professional only.
All Gas Piping & Appliance Load tools →Plumbing Project Cost & Repair
Budget from your own quotes: whole-house repipe cost, bathroom / kitchen rough-in cost, plumbing repair cost, a PEX vs copper comparison, a cost-per-fixture normalizer, and a project budget allocator.
All Plumbing Project Cost & Repair tools →Water Heater — Sizing & Cost
Water Supply & Pipe Sizing
Drain, Waste & Vent
Fixtures & Water Use
Gas Piping & Appliance Load
Plumbing Project Cost & Repair
Built for the whole interior-plumbing project — and to stay correct forever
PipeCalcs gathers the calculations homeowners, DIYers and buyers reach for across an interior plumbing project — water heater → supply pipe sizing → drain, waste & vent → fixtures & water use → gas piping → plumbing project cost — in one focused hub, in US units, without signup, with transparent formulas. Every tool shows not just the answer but the underlying formula, a worked example and a reference table.
Because the tools rest on timeless plumbing math (tankless BTU/hr = GPM × 500 × temperature rise; recovery GPH = BTU/hr × efficiency ÷ (8.34 × ΔT); pressure head = psi × 2.31; pipe volume = 0.0408 × diameter² × length; drain fall = length × slope; gas CFH = BTU/hr ÷ heating value; cost = quantity × your unit price) and stable conventions (7.48 gallons per cubic foot; 1 psi = 2.31 ft of head; nat-gas 1000 / propane 2516 BTU per cubic foot; WSFU → peak-GPM, DFU → pipe-size and gas-capacity planning bands), they stay correct with no maintenance — no material or service price list, no labor-rate database, no regional cost index, no live loan rate. Cost tools use the prices you enter from your own quotes and bills. More at Sources & formulas, Methodology and About. Planning a whole-room remodel budget? That is a different job — see the sibling site RenovationCalcs.
Estimates, not bids. Every cost result is a planning estimate — get itemized written quotes from licensed plumbers. Pipe, drain, vent and gas sizing follows standard conventions, but your local plumbing code and inspector govern — confirm with a licensed plumber and pull the required permits. All gas work must be done by a licensed professional with a permit and inspection. Savings and comparison tools are illustrative math on your figures, not financial advice.