PSI to GPM Calculator
Estimate flow in gallons per minute from pressure, using a nozzle K-factor or an orifice size.
Flow against pressure at K = 5.6
| Pressure | Flow | Metric |
|---|---|---|
| 10 psi | 17.71 gpm | 67 L/min |
| 20 psi | 25.04 gpm | 94.8 L/min |
| 30 psi | 30.67 gpm | 116.1 L/min |
| 40 psi | 35.42 gpm | 134.1 L/min |
| 50 psi | 39.6 gpm | 149.9 L/min |
| 60 psi | 43.38 gpm | 164.2 L/min |
| 80 psi | 50.09 gpm | 189.6 L/min |
| 100 psi | 56 gpm | 212 L/min |
PSI is not a flow rate
Pressure and flow are different quantities. A dead-ended pipe can sit at 100 psi with zero flow. What turns pressure into flow is the restriction it pushes through, so every honest psi-to-gpm calculation needs a second input describing the opening.
The K-factor form
Sprinkler and spray nozzles are specified by a discharge coefficient K that already bundles the geometry:
Q = K × √P
A K = 5.6 head at 50 psi flows 5.6 × √50 = 39.6 gpm.
This is the standard form in fire-protection design (NFPA 13) and the numbers come
straight off the data sheet.
The orifice form
For a plain hole in a plate, with water:
Q = 29.84 × Cd × d² × √P
with d in inches and P in psi. The discharge coefficient accounts for the jet contracting as it leaves — about 0.62 for a sharp-edged hole, rising towards 0.98 for a smoothly rounded nozzle. Note the square on the diameter: doubling the hole quadruples the flow.
Why doubling pressure does not double flow
Flow goes as the square root of pressure. To double the flow you need four times the pressure. Going from 50 to 100 psi raises flow by only about 41%, which is why pressure alone is an inefficient way to buy more throughput — a bigger orifice does far more.
These are estimates for water at ordinary temperatures. Real installations lose pressure to pipe friction, fittings and elevation, so the pressure at the nozzle is lower than at the source. Size systems from measured residual pressure, not static pressure.