Fire Nozzle Flow Rate Chart — GPM, LPM, PSI & Bar Conversions

Fire nozzle specifications are written in different units depending on the country, the standard, and the era of the equipment. NFPA standards use US gallons per minute (GPM) and pounds per square inch (PSI). European standards use litres per minute (LPM) and bar. Chinese standards use LPM and megapascal (MPa). The same nozzle delivering 500 LPM at 7 bar might be listed as 132 GPM at 100 PSI, or 0.7 MPa, depending on whose datasheet you are reading.

This is more than a labelling problem. Fire pump sizing, water supply calculations, and pressure loss budgeting all depend on consistent units. Mixing units mid-calculation produces flow predictions that are 4x off in either direction. This guide gives the conversion tables and the calculation framework — and explains what flow rate to design for in different fire scenarios.

1. Units & Conversion Constants

The fire fighting industry uses four flow rate units and three pressure units in active practice. Before any calculation, fix the conversion constants:

Watch out for US vs UK gallons. US gallon = 3.785 litres. UK (imperial) gallon = 4.546 litres. NFPA documents and US-market equipment use US gallons; older UK and Commonwealth documents use imperial. Always confirm which gallon you are working in — the 20% difference will show up as a 20% miss in your supply calculation.

2. GPM ↔ LPM Conversion Table

The standard flow rates that appear on most fire nozzle specifications, with US GPM and LPM cross-referenced:

This table covers the full range of CA-FIRE handheld nozzles. Above 1,600 LPM you are into fire monitor territory — fixed and portable cannons covering 1,500 to 4,800 LPM (25–80 L/s).

3. Pressure Conversion (Bar / PSI / MPa)

The standard nozzle inlet pressures and their conversions:

Note the inline foam eductor pressure of 14 bar — this is significantly higher than the 7 bar of a standard nozzle because the eductor’s venturi consumes 30–40% of the inlet pressure to draw foam concentrate from the suction tube. When sizing the pump for a system that includes inline foam eductors, design for the eductor inlet pressure, not the nozzle pressure. See our foam nozzle specifications for the FE095/FE125/FE250 inlet pressure requirements.

4. K-Factor — The Master Equation

The fundamental equation connecting flow rate to pressure for any fire nozzle or sprinkler head is:

The K-factor is the nozzle’s flow constant — a property of its orifice geometry. Given a nozzle’s K-factor and the inlet pressure, you can calculate the flow rate. Given a nozzle’s K-factor and a required flow rate, you can calculate the inlet pressure needed.

Unit convention matters. K-factor values are unit-dependent. The most common conventions in the fire industry:

• K (metric): Q in LPM, P in bar → K typically ranges 20–100 for handheld nozzles
• K (NFPA / US): Q in US GPM, P in PSI → K typically ranges 5–25 for handheld nozzles
• K (Chinese standard): Q in LPM, P in MPa → K typically ranges 60–300

The CA-FIRE PQ 2 low-expansion foam nozzle, for example, has a metric K-factor of 43.4 (Q in LPM, P in bar). At rated 8 bar (0.8 MPa) inlet, that gives Q = 43.4 × √8 = 43.4 × 2.83 = 123 LPM (close to the listed 120 LPM). At a hypothetical 6 bar inlet, Q = 43.4 × √6 = 43.4 × 2.45 = 106 LPM — the same nozzle at lower pressure delivers less flow.

For practical design work, K-factor is the bridge between supply pressure and discharge flow. If the building’s available residual pressure is known and a target flow is specified, K-factor tells you which nozzle to spec. If a specific nozzle is already specified and the supply pressure is variable, K-factor tells you the flow variation to expect.

5. CA-FIRE Nozzle Flow Reference Chart

Quick reference for CA-FIRE handheld nozzle flow at rated pressure. Use this to match a nozzle to a required flow rate, or to verify that a specified nozzle’s flow matches your design.

6. Recommended Flow by Fire Scenario

The recommended flow for a fire incident depends on the fuel load, the area involved, and the construction type. The values below are typical industry rules of thumb — confirm against your local fire engineering analysis:

These are starting numbers for design. Local fire codes (NFPA 13/14/24, EN 12845, GB 50261) include detailed prescriptive requirements for specific occupancy and hazard classes. For projects above warehouse scale, a fire engineering consultant should perform a fire load calculation rather than relying on rules of thumb.

7. Hose Friction Loss — The Missing Variable

The nozzle pressure is what the nozzle sees, not what the pump puts out. Between the pump and the nozzle there is hose, and the hose absorbs pressure to friction loss. Underestimating friction loss is the most common error in fire pump sizing.

The standard NFPA formula for friction loss in a single 100-foot section of hose is:

Typical friction coefficient (C) values for standard fire hose:

• 1.5″ hose: C = 24
• 1.75″ hose: C = 15.5
• 2″ hose: C = 8
• 2.5″ hose: C = 2
• 3″ hose: C = 0.8
• 4″ hose: C = 0.2

The big takeaway: doubling the hose diameter from 1.5″ to 3″ reduces friction loss by a factor of 30. For long hose lays (over 100 metres / 300 feet), the choice of hose size dominates the supply pressure equation. A 100-foot 1.5″ hose flowing 100 GPM loses 24 × 1² × 1 = 24 PSI to friction. The same length 2.5″ hose at the same flow loses 2 × 1² × 1 = 2 PSI. Hose size selection is real pump money.

8. Worked Example — Pump to Nozzle

A worked example combining everything in this guide. Scenario: 12-storey building, fire on the 10th floor, design flow 475 LPM (125 GPM), using a CA-FIRE QLD6.0/8III-B adjustable nozzle.

This example demonstrates why nozzle pressure rating alone does not determine pump sizing — elevation and friction together represent the majority of the pressure budget on tall buildings. For a 30-storey building the elevation alone consumes nearly 100 PSI of the supply pressure.

9. FAQ

What is the difference between GPM and LPM in fire nozzles?

GPM is gallons per minute, used in NFPA and US standards. LPM is litres per minute, used in EN, BS and GB standards. 1 US GPM = 3.785 LPM, so a nozzle rated at 100 GPM delivers 378.5 LPM. UK imperial GPM is different — 1 UK GPM = 4.546 LPM — so always confirm which gallon you are working in. NFPA documents use US GPM by default.

What is the standard fire nozzle pressure?

The international standard for handheld adjustable fire nozzles is 7 bar (100 PSI / 0.7 MPa). This is the inlet pressure at which the nozzle is designed to deliver its rated flow and reach. Smooth-bore traditional jet nozzles are typically rated at the lower 3.5 bar (50 PSI / 0.35 MPa). Foam nozzles are typically 7–8 bar at the nozzle, but inline foam eductors require 14 bar (200 PSI) inlet pressure to drive the venturi. CA-FIRE handheld fire hose nozzles use the standard 7 bar working pressure across the QLD adjustable range.

How do I calculate fire nozzle flow rate from pressure?

Use the K-factor equation: Q = K × √P, where Q is flow rate, K is the nozzle’s flow constant, and P is the inlet pressure. K-factor is a property of the nozzle geometry — given by the manufacturer’s specification. Important: K-factor is unit-dependent. Metric K (Q in LPM, P in bar), NFPA K (Q in US GPM, P in PSI), and Chinese standard K (Q in LPM, P in MPa) all give different numerical values for the same physical nozzle. Always confirm which unit system the K-factor was specified in.

What flow rate do I need for a structure fire?

The Iowa State University formula suggests roughly 1 GPM per 100 cubic feet of involved compartment for structural fires — a useful rule of thumb. In practice: residential room and contents needs 30–60 GPM (115–230 LPM); commercial office needs 60–95 GPM (230–360 LPM); light industrial needs 95–125 GPM (360–475 LPM); warehouse and petrochemical scenarios need 125+ GPM (475+ LPM). Local fire codes (NFPA 13/14/24, EN 12845, GB 50261) provide prescriptive requirements based on occupancy class and hazard.

How much pressure does fire hose lose to friction?

Use the NFPA formula FL = C × (Q/100)² × L, where FL is friction loss in PSI, C is the friction coefficient (depends on hose size), Q is flow in GPM, and L is hose length in hundreds of feet. Typical C values: 1.5″ hose = 24, 1.75″ = 15.5, 2″ = 8, 2.5″ = 2, 3″ = 0.8, 4″ = 0.2. The strong dependence on hose diameter (C drops 30× from 1.5″ to 3″) means hose size selection dominates friction loss on long hose lays.

What is L/s in fire nozzle ratings?

L/s is litres per second, used primarily in Chinese national standards (GB) and some European industrial specifications. 1 L/s = 60 LPM = 15.85 US GPM. The CA-FIRE QZG3.5/7.5 jet nozzle, for example, is rated at 7.5 L/s which equals 450 LPM or 119 US GPM. Fire monitors and water cannons are typically rated in L/s rather than LPM because their flows are much higher (20–80 L/s = 1,200–4,800 LPM).

When does flow rate exceed handheld nozzle capability?

Handheld fire nozzles cover the range from 50 LPM (small reel-line) up to about 1,600 LPM (large water curtain) for sustained one or two-person operation. Beyond 1,600 LPM the nozzle reaction force becomes too high for handheld operation — typical limit is 70 kg / 150 lb reaction force. For higher flows the application switches to fixed or portable fire monitors and water cannons, which use a swivel mount or pedestal to absorb the reaction force rather than relying on the operator’s strength.