Gallons Per Minute Calculator
Calculate water flow rate in gallons per minute (GPM) from volume and time. Free online GPM calculator with flow rate conversions to LPM, GPH, and more for plumbing, irrigation, and pump sizing.
About This Calculator
The Gallons Per Minute (GPM) calculator measures the volumetric flow rate of water or other liquids — how many gallons pass through a point every minute. Flow rate is a critical metric in plumbing, irrigation, HVAC, well pump sizing, and industrial fluid systems. Whether you are sizing a pump for your home, checking your shower's water consumption, or designing an irrigation system for your garden, knowing the GPM helps you select the right equipment and manage water usage efficiently.
This calculator uses the standard flow rate formula: Flow Rate (GPM) = Volume (gallons) ÷ Time (minutes). Enter the volume of water collected or flowing through a system in gallons and the time in minutes it took to collect that volume. The calculator instantly computes the flow rate in gallons per minute (GPM) and provides additional conversions to liters per minute (LPM) and gallons per hour (GPH) for your convenience.
The conversion factors are: 1 US gallon = 3.78541 liters for GPM to LPM conversion, and 1 hour = 60 minutes for GPM to GPH conversion. Our calculator displays all three units alongside each other so you can reference whichever unit your equipment or local standards use.
Regional Notes
United States: GPM is the standard unit for flow rate in US plumbing codes. Typical residential water supply delivers 6-12 GPM. Showerheads are regulated at a maximum of 2.0 GPM (federal standard). Garden hoses typically provide 9-17 GPM depending on diameter and pressure.
United Kingdom: Flow rates are commonly measured in liters per minute (LPM). 1 UK imperial gallon = 4.546 liters (larger than US gallon). Typical household mains water flow ranges from 10-20 LPM. Combination boilers require a minimum flow rate of about 10 LPM to operate efficiently.
India: Flow rates are measured in liters per minute (LPM) or liters per second (LPS). Municipal water supply varies widely from 5-20 LPM depending on locality. Borewell pumps are rated in HP with typical residential pumps delivering 10-30 LPM. Overhead tank filling times depend on pump flow rate and tank capacity.
Frequently Asked Questions
What is GPM (gallons per minute)?
GPM stands for gallons per minute, a unit of volumetric flow rate used to measure how fast a liquid — typically water — moves through a pipe, pump, showerhead, faucet, or hose. One GPM means one US gallon (3.785 liters) flows past a point every minute.
How do I calculate gallons per minute?
To calculate gallons per minute, collect a known volume of water in a container and record the time in seconds it takes to fill it. Convert the volume to gallons (1 US gallon = 3.785 liters) and the time to minutes. Then use the formula: GPM = Volume (gallons) ÷ Time (minutes). For quick results, enter the volume and time into our GPM calculator above.
What is the formula for GPM?
The GPM formula is simple: Flow Rate (GPM) = Volume (gallons) ÷ Time (minutes). For example, if you collect 10 gallons of water in 2 minutes, the flow rate is 10 ÷ 2 = 5 GPM. You can rearrange this formula to find volume (GPM × time) or time (volume ÷ GPM) depending on what you need.
How many GPM does a standard shower use?
Standard showerheads in the US have a flow rate of approximately 2.0 GPM (gallons per minute). Water-saving showerheads are rated at 2.0 GPM or less under federal regulations. In the UK, shower flow rates typically range from 1.5 to 3.0 GPM (6 to 13 liters per minute), depending on water pressure and shower type.
How many GPM does a garden hose produce?
A typical garden hose produces between 9 and 17 GPM depending on hose diameter, length, and water pressure. A 5/8-inch hose at 40-60 PSI usually delivers around 10-12 GPM, while a 1/2-inch hose produces about 6-9 GPM. Longer hoses reduce flow due to friction loss.
How do I convert GPM to LPM?
To convert GPM (US gallons per minute) to LPM (liters per minute), multiply by 3.78541. One US gallon equals 3.78541 liters. For example, 5 GPM × 3.78541 = 18.93 LPM. To convert LPM to GPM, divide by 3.78541. Our calculator shows both GPM and LPM values automatically.
What is a good flow rate for a well pump?
A good well pump flow rate depends on household size and water needs. The average US household requires 6-12 GPM for daily use. A 3-4 bedroom home with 2-3 bathrooms typically needs 8-12 GPM peak flow. In the UK and India, where metric measurements are standard, the equivalent is roughly 23-45 liters per minute.
How many GPM does a washing machine use?
A standard washing machine uses approximately 3 to 5 GPM during the fill cycle. High-efficiency front-loading washers use less water, typically 2-3 GPM, because they use tumbling action rather than full submersion. The total water consumption per load ranges from 15-30 gallons depending on the machine type and cycle selected.