PSI to GPM Calculator

What is a PSI to GPM calculator?

A PSI to GPM calculator helps you estimate how much flow a nozzle, sprinkler, orifice, or similar device can deliver when you know both the applied pressure and the device K-factor. It is useful for quick field checks, rough comparisons, equipment checks, and reading manufacturer data without doing the square-root math by hand every time.

The most important point is that this is not a simple pressure-to-flow unit conversion. The same 50 PSI can produce different GPM values depending on whether the device K-factor is 5.6, 8.0, 11.2, or something else. That is why this tool asks for both pressure + K-factor before calculating estimated flow.

When to use it

Pressure-to-flow relationships show up often in practical equipment work, but they are not always easy to estimate in your head. Because flow changes with the square root of pressure instead of in a straight line, a calculator or comparison table can make comparisons much faster and easier.

• Reading manufacturer data – Estimate flow quickly from a listed K-factor and pressure point
• Comparing sprinklers or nozzles – See how different K-factors change flow at the same pressure
• Field notes – Estimate rough flow after measuring pressure at the device location
• Training or education – Understand how Q = K × √P behaves with real numbers
• Reference comparison – Compare PSI-based and GPM-based references on the same basis

Key features

After you enter pressure and K-factor, the tool shows the main estimate first in the top result card, then organizes liter conversions and pressure comparisons below it. That makes it easier to read both the current result and how it sits among common reference pressure points.

• Instant PSI + K-factor calculation – Estimate flow in GPM using a US K-factor
• Liter conversions included – Check GPM together with L/min and L/s
• Quick pressure and K-factor presets – Load common input points with one click
• Pressure comparison bars – See how estimated flow changes across common pressures
• Table plus explanation – Check the data table, formula notes, unit cautions, and FAQ together

How to use

Start by entering the US K-factor for your device and the measured or target pressure in PSI. After you click Calculate, the tool shows the estimated flow in GPM in the top result card first, then lets you check the liter conversions and pressure comparison table below.

1. Enter pressure: Input the pressure at the device location in PSI.
2. Enter K-factor: Check the device data sheet and enter the US K-factor.
3. Run the calculation: Click Calculate to display the estimated flow for the current input.
4. Check the result: Read GPM first in the top result card, then check L/min and L/s in the result cards below.
5. Check the comparison: Use the bars and table to see how flow changes when pressure changes.

If the manufacturer data sheet only lists a metric K-factor, it is safer to confirm the matching US K-factor before entering a value here. This calculator is designed for US K-factor input.

PSI to GPM calculator details (formula and interpretation)

Checked on: 2026-03-12
Reference sources: Viking Group technical data, NIST Guide to the SI Appendix B conversion factors.

The base formula used here is Q = K × √P. In that formula, Q is flow in gallons per minute (GPM), K is the device US K-factor, and P is pressure in psi at the device location. In other words, pressure alone does not determine flow. You need the device K-factor as well.

The relationship between pressure and flow is not linear. It follows a square-root relationship. For example, if pressure rises from 25 psi to 100 psi while K stays the same, pressure becomes 4 times higher but flow becomes only 2 times higher. On the other hand, if the K-factor doubles, flow also doubles at the same pressure. That is why K and P should always be checked together.

For example, if K = 5.6 and P = 50 psi, then Q = 5.6 × √50 ≈ 39.6 GPM. That is about 149.9 L/min, or roughly 2.50 L/s. This is useful for quick comparison, but final design, commissioning, and verification should also account for the allowable pressure range, spray pattern, pipe loss, and actual residual pressure at the device.

Many manufacturer documents list both metric K-factor (L/min/√bar) and US K-factor (gpm/√psi). Even if the numbers look similar, they are not interchangeable. Always confirm that the K value entered in this calculator is a US K-factor. For final decisions, use the exact manufacturer data sheet and installation criteria for the device you are checking.

• K 5.6 at 25 psi: 5.6 × √25 = 28.0 GPM
• K 5.6 at 100 psi: 5.6 × √100 = 56.0 GPM
• Pressure 25 → 100 psi: pressure is 4× higher, flow is 2× higher
• K 5.6 → K 11.2: flow doubles at the same pressure

Frequently asked questions