Both calculators involve gallons per minute, but they answer different questions. The flow rate converter changes the units of a volumetric flow you already know — say, from gallons per minute to liters per minute — using exact, defined unit relationships. The PSI to GPM calculator starts from pressure and opening size and estimates how much water would flow through a circular opening under ideal assumptions. One translates a rate; the other estimates a rate from physics.
What each calculator does
The flow rate converter takes a nonnegative flow value and converts it among four units: cubic meters per second, liters per minute, U.S. gallons per minute, and cubic feet per minute. Every input passes through m³/s using the factors 0.001 ÷ 60 for L/min, 0.003785411784 ÷ 60 for US gal/min, and 0.3048³ ÷ 60 for ft³/min, then divides by the target factor. The result is rounded for display — m³/s to six decimals and the other units to three. The page’s worked example shows 25 US gal/min converting to 94.6352946 L/min before rounding, with the same input shown as 3.342 ft³/min.
The PSI to GPM calculator is not a unit converter. It estimates water flow through a circular opening from three inputs: upstream pressure, exit pressure, and opening diameter. It converts the diameter to feet, computes the circular area, and finds the ideal velocity as the square root of the pressure drop times 32.174 ft/s², 144, and 2, divided by 62.4 lb/ft³ — the standard-gravity, water-density constants. Velocity times area gives cubic feet per second, and multiplying by 448.83 converts that to gallons per minute. With the default inputs of 60 psi upstream, 14.7 psi exit, and a 1-inch opening, the ideal flow is about 200.78 gpm, alongside the pressure drop, area, velocity, and cubic-feet-per-second outputs.
Side-by-side
| Flow rate converter | PSI to GPM calculator | |
|---|---|---|
| Inputs | Flow value plus source and target units | Upstream pressure, exit pressure, opening diameter |
| Primary output | The same flow in the selected unit | Ideal water flow in gpm, plus pressure drop, area, velocity, and cfs |
| Nature of the result | Exact unit conversion with defined volume factors | Ideal Bernoulli-style estimate for water through a circular opening |
| Units supported | m³/s, L/min, US gal/min, ft³/min | Gallons per minute and cubic feet per second from the estimate |
| Assumptions | None beyond the unit definitions | Water, no friction, no nozzle coefficient, no elevation change |
| Typical uses | Converting a known pump or meter rate for reports and specs | First-pass estimate for tanks, short outlets, nozzles, and opening comparisons |
| Domain rules | Rejects negative flow values | Requires upstream pressure to exceed exit pressure |
When to use which
Use the flow rate converter when you already have a flow number — from a pump label, meter reading, or spec sheet — and need it expressed in different units. Its result is exact unit arithmetic, so it is the right tool for reports, conversions between metric and US flow units, and any task where the rate itself is known.
Use the PSI to GPM calculator when your data is pressure and a circular opening, not an existing flow reading. It is explicitly an ideal upper-bound estimate: pipe roughness, hose length, valves, elbows, and nozzle shape usually lower real flow, sometimes by a large margin. Treat it as a comparison and rough-sizing tool for short outlets and test rigs, not as the final answer for municipal service lines, irrigation zones, fire protection, or long hoses.
Limits and disclaimer
The flow rate converter handles volume-per-time only — it does not convert pressure or mass flow, and it rejects negative values. The PSI to GPM calculator bakes water density into its constants, so it is not valid for compressed air, steam, or natural gas, and it shows a validation message when upstream pressure is not greater than exit pressure. Its rounded constants (32.174, 62.4, 144, 448.83) are common engineering approximations, and the result is an estimate, not a measurement. Neither page replaces professional pipe-sizing, pump-selection, or pressure-engineering work.