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Tank, pipe, friction, tankless, and well-pump calculators
How much a tank holds, how much a run of pipe holds, how much head the flow gives up, what a tankless heater has to deliver, the duty point a well pump has to meet, and the GPM a bucket or a pipe is moving.
Tank Volume Calculator
Tank volume calculator for vertical and horizontal cylinders and rectangular tanks, with a dipstick chart for a partly full horizontal tank.
Pipe Volume Calculator
Pipe volume calculator by nominal size. Schedule 40 and 80 steel, copper types K, L, and M, and SDR-9 PEX.
Friction Loss Calculator
Friction loss calculator using Hazen–Williams and Darcy–Weisbach, plus fittings as equivalent length.
Tankless Water Heater Size Calculator
Tankless water heater size from simultaneous fixture flow and temperature rise. Gas input in BTU/h, or electric kilowatts and amps. A sizing estimate, not gas-pipe or wire sizing.
Well Pump Size Calculator
Well pump planning size from flow and total dynamic head. Duty point, friction loss, and a horsepower to check on a manufacturer curve. Not a pump selection and not a wire size.
Flow Rate Calculator
Flow rate calculator for a bucket test, pipe velocity, and free discharge from an open outlet. Not a fire-flow test and not a medical calculator.
How these calculators work
A vertical cylinder is the circle times the fill height. A rectangular tank is length times width times fill. A horizontal cylinder uses the circular segment: the area of the filled part of the circle, times the length. The dipstick chart repeats that at each tenth of the diameter. Gallons are cubic feet times 7.48052.
Pipe volume uses an inside diameter from a published table. Steel is ASME B36.10 Schedule 40 and Schedule 80. Copper is ASTM B88 types K, L, and M. PEX is ASTM F876 SDR-9, wall equal to the outside diameter divided by 9. The stamp on the tube wins if it disagrees. Friction loss runs Hazen–Williams, with a C factor, and Darcy–Weisbach with the Swamee–Jain friction factor. Fittings are added as an equivalent length. A published K or Cv for that fitting wins. The well-pump page reuses that Hazen–Williams line for the drop pipe and the run to the house.
Tankless size is simultaneous fixture flow times the temperature rise. Output is 500 × gpm × °F rise. Gas input divides by thermal efficiency and flags a single residential unit above 199,900 BTU/h. Electric input is kilowatts and amps only, with no breaker or wire recommendation. The well-pump page adds pumping level, elevation, pressure-switch head, and that friction into total dynamic head, then a horsepower to check on a manufacturer curve.
Flow rate is a bucket test, pipe velocity times area, or free discharge from an open outlet. The open-outlet formula is not a fire-flow test. Velocity bands are guidance, not code.