One pipe run, many questions: what flow the bore delivers, whether the velocity sits in its band, how much pressure the friction spends, and what the pump pays. Every section reads the same inputs — so the numbers can never quietly disagree with each other the way figures copied from three different websites do.
This is the engine the whole site runs on. Its left panel solves volumetric and mass flow together — Q = A·v and ṁ = ρ·Q — from any of four cross-sections: circular pipe, rectangular duct, a half-full open channel through its hydraulic diameter, or an area you define yourself. Its right panel reports what the flow costs: Reynolds number and regime, Darcy–Weisbach head loss with the Colebrook–White friction factor, pressure drop for the run and per 100 m, and the pump power to overcome it.
The presets do the tedious part. Nineteen fluids arrive with density and viscosity corrected to your operating temperature; standard schedules — NPS Sch 40/80, PVC Sch 40/80, copper Type K/L/M, PEX CTS, hose — fill the true inside diameter the moment you pick one; gases convert between SCFM, Nm³/h, and ACFM at your line conditions. Every result keeps both unit systems visible, and nothing hides behind an account.
Reach for it when…
Q = A·v and ṁ = ρ·Q solved together: enter any two of area, velocity, and flow, and the third follows on the same keystroke.
Circular pipe, rectangular duct, half-full open channel, or a custom area — non-round sections are handled through Dₕ = 4A/P.
Water, diesel, glycerin, honey, mercury, molten PLA; air, natural gas, nitrogen, CO₂, hydrogen, propane — density and viscosity move with your operating temperature.
SCFM and Nm³/h at reference conditions, converted live to ACFM at your line pressure and temperature — no chart, no mental arithmetic.
NPS Schedule 40/80, PVC Sch 40/80, copper Type K/L/M, PEX CTS, and hose presets fill the true ID instead of a nominal guess.
Regime detection, Darcy–Weisbach loss with the Colebrook–White friction factor from your material's roughness, ΔP for the run and per 100 m, and pump power.
Home main line, drip tape, aquarium, garden hose, HVAC duct, gutter, gas line, 3D-printer nozzle — each with its recommended velocity band and a warning when you leave it.
Six directions, ordered the way a flow problem unfolds — the geometry first, then the fluid, then the conditions, then what the flow costs. Each card links to the home-page section where that capability lives today, inside the main calculator and its reference sections.
Nominal size is a label, not a dimension — a 1-inch line is never 1.000 inches inside. This direction covers the schedule system, measuring true inside diameter, and the hydraulic diameter that lets one engine handle round pipe, rectangular duct, and open channel alike.
See the size presetsDensity and viscosity are the two numbers every result inherits, and both move with temperature. From chilled water to honey to molten PLA, the 19 presets carry values corrected to your operating conditions — and a custom row accepts your own fluid entirely.
Meet the fluid presetsA cubic metre of gas is only defined once you name its pressure and temperature. SCFM, Nm³/h, and ACFM answer the same question at three reference states — the engine converts between them from your operating conditions using the ideal-gas law.
Convert SCFM and ACFMVelocity is where sizing decisions live: too slow and solids settle, too fast and the line hammers, erodes, and roars. Reynolds number turns the same velocity into a flow regime — laminar, transitional, or turbulent — that decides which friction law applies.
Check the velocity bandsEvery metre of pipe charges rent in pressure. Darcy–Weisbach with the Colebrook–White friction factor prices that rent from length, roughness, and velocity — and the pump-power line converts the head loss into the watts you actually pay for.
Price the pressure dropA drip emitter, a gutter downspout, and a 3D-printer nozzle obey the same equation at wildly different scales. Nine scenario presets load the geometry, the fluid, and a recommended velocity band, so the answer arrives with its engineering context attached.
Browse the scenariosNarrow, job-specific calculators that share the same engine — each with its own presets, warnings, and worked examples. They ship into the registry below as they are finished.
Calculate flow rate from pressure and pipe diameter — Darcy-Weisbach iteration, Hazen-Williams water formula, orifice equation with C-value table.
Open calculatorDarcy-Weisbach pressure drop calculation from flow rate — Colebrook-White friction factor with pipe roughness table, local losses, and pump power.
Open calculatorSize a pipe from flow rate using target velocity bands, d = √(4Q/πv), and schedule selection — Sch40 vs Sch80 ID comparison.
Open calculatorCalculate flow rate through orifices, nozzles, and valves — Q = C_d·A·√(2ΔP/ρ), C_d tables, critical gas flow, Cv/Kv correlation.
Open calculatorCompressed air flow rate calculator: ACFM/SCFM conversion, Darcy-Weisbach gas density correction, header sizing, and compressor FAD.
Open calculatorGarden hose GPM flow rate by nominal size (5/8″ 3/4″ 1″), water pressure, and hose length. Drip and sprinkler budget.
Open calculatorIn the meantime, the single engine already answers these jobs: pick a scenario preset on the applications section of the home page and the inputs, the fluid, and the velocity band load together.
The test of a shared engine is simple: run the same pipe through every lens and the story has to stay consistent. Here is 40 ft of 1″ Type L copper carrying water at 20 °C, targeted at the 1.5 m/s a domestic supply line should see — through the figures it meets on the way to a verdict. Every number traces back to the same inputs, and you can reproduce each one in the tool that names it.
532.7 mm²
A = πd²/4 for the 26.0 mm true inside diameter of 1″ Type L copper. The schedule preset fills it — no chart lookup, no nominal guess.
0.80 L/s · 12.7 GPM
Q = A·v at the 1.5 m/s the engine targets for domestic water supply — the same velocity the application preset recommends for a home branch.
0.80 kg/s
ṁ = ρ·Q with water density corrected to 20 °C — the left-hand panel of the calculator, solved from the same inputs with no re-entry.
≈39,000 · Turbulent
Re = ρvD/μ lands far past the Re 4,000 boundary, so the Colebrook–White friction factor — not the laminar 64/Re shortcut — governs the loss.
≈11.6 kPa over 40 ft
Darcy–Weisbach with f ≈ 0.022 for drawn copper roughness — about 95 kPa per 100 m, shown both for the full run and normalised per 100 m.
PASS · mid-range
1.5 m/s sits inside the 1.0–2.5 m/s domestic supply band — slow enough to avoid water hammer, fast enough to keep sediment moving.
Same line, every lens, every timePhoto: UnsplashThe classic failure is not one bad number — it is two good numbers that were never talking. A flow taken from a generic chart, a velocity assumed from a nominal diameter, a pressure drop scaled from a different fluid. Each is an honest estimate made in isolation; stacked together they produce a branch that starves a shower, a drip zone that never equalises, or a pump that cavitates.
Sharing one engine is the structural fix. The schedule that set your diameter also sets your area; the fluid preset that set your density also set your Reynolds number; the velocity that sized your flow also priced your friction. When the definitions are shared, the mistakes get caught by arithmetic instead of by the commissioning crew.
See more worked examplesFind the question you are holding, follow the row, open the section. Every destination is one click away — and back to the main calculator when the next question starts.
Every tool has a guide behind itPhoto: UnsplashEvery capability on this page has a matching set of guides that explain the ideas behind its inputs — why nominal and true diameter differ, how temperature rewrites viscosity, where SCFM and ACFM part ways, and what a Reynolds number is really telling you about the line.
The guides and the tools are written as a pair: the reading explains why a number moves, the tool shows how far it moves. If a result ever surprises you, the guide library is the fastest way to find out whether the surprise is the math or the measurement.
Browse the guide libraryYes — every tool on this page is free, requires no account, and has no usage caps or paywalled fields. The site is a reference toolset, not a lead-generation funnel: nothing gates a result, and no result is emailed to anyone.
One engine, several lenses. The flow result, the gas conversions, the Reynolds check, and the friction loss all read the same diameter, fluid, and velocity data you enter, so a figure from one section is always consistent with the others. There is no second copy of the math to drift out of date — and no re-typing your line when you switch sections.
Volumetric and mass flow from any cross-section, gas flow at standard and actual conditions (SCFM, Nm³/h, ACFM), Reynolds number with regime detection, Darcy–Weisbach pressure drop with the Colebrook–White friction factor, and pump power. Dedicated calculators for narrower jobs are queued in the registry below and will appear there automatically as they ship.
The 19 presets carry reference density and viscosity for each fluid — water, diesel, glycerin, honey, mercury, molten PLA, air, natural gas, nitrogen, CO₂, hydrogen, propane, and more — corrected to your operating temperature and pressure. Real fluids vary with composition, so the preset is a starting point and a custom density or viscosity you enter yourself is the authority.
Yes. Switch the unit system and the inputs and outputs all move together — millimetres, litres per second, and kilograms per hour in, or GPM and SCFM if the specification you were handed is imperial. Both unit sets stay visible on results, so a metric drawing can still be checked against an imperial nameplate.
Please do. Send the calculation you keep doing by hand — what inputs you start from, what result you need out — through the contact page. Requests that describe a real, repeated flow problem go to the top of the queue, and the toolset grows the same way the guide library does: from questions that were worth writing down.
Pick a pipe size, pick a fluid, set the velocity — the engine returns the flow rate, the Reynolds regime, the pressure drop, and the pump power in one keystroke. Free, private, and instant.