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Flow Rate Converter GPM to LPM

1 GPM (US) = 3.785412 LPM (Liters/min)

Example: Standard faucet limits at 2.2 GPM correspond to 8.33 LPM.

Flow Converter

GPM
LPM

Pipe Velocity Estimator

(1.049" is typical for 1" Sch 40 steel pipe)
Flow Velocity 3.7 ft/s
(1.13 m/s)

GPM to LPM Reference Matrix

GPM (US) Equivalent LPM Application Context
1 GPM 3.79 LPM Standard household faucet
2.5 GPM 9.46 LPM Low-flow shower head limit
5 GPM 18.93 LPM Residential garden hose
15 GPM 56.78 LPM Standard fire sprinkler head
50 GPM 189.27 LPM Commercial water main supply

GPM vs LPM: Understanding the Difference

GPM (Gallons Per Minute) is the US customary unit for volumetric flow rate, commonly used in plumbing, HVAC, and irrigation. LPM (Liters Per Minute) is the SI metric equivalent, standard in most countries outside the United States.

Quick Conversion: LPM = GPM × 3.785
Reverse: GPM = LPM × 0.2642
Note: 1 US gallon = 3.785 liters (1 Imperial gallon = 4.546 liters)

Pipe Velocity and System Design

Water velocity inside pipes directly impacts system performance. The velocity formula used in this calculator is: V (ft/s) = (0.4085 × GPM) / D², where D is inside diameter in inches. This is derived from the continuity equation Q = A × V.

Excessive velocity (>8 ft/s) causes water hammer, pipe erosion, and excessive noise. Too low velocity (<2 ft/s) may allow sediment settling. Design for 4-5 ft/s for cold water mains and 3-4 ft/s for hot water lines.

Frequently Asked Questions — Flow Rate Conversion

How do you convert GPM to LPM?
Multiply the GPM value by 3.785412 to calculate Liters per Minute. Formula: LPM = GPM × 3.785412. For quick estimates, multiply GPM by 3.785. Example: 10 GPM × 3.785 = 37.85 LPM.
What is 10 GPM in LPM?
10 GPM is equal to approximately 37.85 LPM. This flow rate is typical for a residential garden hose running at full pressure.
How do you calculate water flow rate in a pipe?
Flow rate (GPM) = Velocity (ft/s) × Cross-sectional area (ft²) × 448.8. Alternatively, use Q = A × v where A is pipe cross-section in square inches and v is velocity in ft/s, then divide by 0.4085 for GPM.
What is the typical water flow rate for a household faucet?
Standard residential faucets flow at 2.2 GPM (8.3 LPM) maximum per EPA WaterSense guidelines. Low-flow models deliver 1.5 GPM (5.7 LPM). Fire sprinkler heads typically flow 15-20 GPM (57-76 LPM).
Why is pipe velocity important in plumbing design?
Pipe velocity affects noise, erosion, and pressure drop. Ideal velocity for cold water is 4-5 ft/s (1.2-1.5 m/s) and for hot water 3-4 ft/s (0.9-1.2 m/s). Velocities above 8 ft/s cause excessive noise and pipe erosion; below 2 ft/s may allow sediment buildup.

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