Gallons Per Minute Calculator (GPM)
Measure your water flow rate accurately with two methods: the bucket test (fill a container and time it) or the pipe velocity method (enter pipe diameter and flow speed). Get results in GPM, gallons per day, gallons per year, liters per minute, and cubic meters per hour. See flow quality ratings and usage estimates for showers, hoses, and irrigation systems.
Choose based on what you can measure
How many gallons your bucket or container holds
How long it takes to fill the container completely
Inside diameter of the pipe
Typical: 3-5 ft/s for copper, 4-6 ft/s for PVC
How do I calculate GPM from a bucket test?
The bucket test is the simplest method: Time how many seconds it takes to fill a known-volume container. Then use GPM = (Container Volume in Gallons ÷ Fill Time in Seconds) × 60. For example, if a 5-gallon bucket fills in 12 seconds: (5 ÷ 12) × 60 = 25 GPM. Take 3 measurements and average them for accuracy. This method works for any faucet, shower, hose bib, or well spigot.
What is a good GPM for a well?
Residential wells typically produce 3-12 GPM. 1 GPM = 1,440 gallons per day, enough for a 3-person household. Recommended minimum: 3 GPM (4,320 gal/day) for a standard home. 5+ GPM is excellent and allows for irrigation. Low-yield wells (under 3 GPM) need a storage tank. Test your well GPM annually. Sandy soils tend to produce higher GPM than clay. Well GPM can drop during drought — factor that into your system design.
What is the flow rate of a standard garden hose?
A standard 5/8-inch garden hose at typical household pressure (40-60 psi) delivers 9-17 GPM. At 50 ft length: 15-17 GPM. At 100 ft: 11-13 GPM. At 200 ft: 7-9 GPM (friction loss reduces flow). A 1/2-inch hose delivers 6-9 GPM; a 3/4-inch hose delivers 18-25 GPM. For sprinklers, most oscillating models need 3-5 GPM; impact sprinklers need 4-8 GPM at 40-50 psi.
What is the normal GPM for a shower head?
Standard US shower heads are limited to 2.5 GPM at 80 psi. Many modern low-flow heads use 1.5-2.0 GPM. Older heads (pre-1994) may flow 4-8 GPM. To measure: time how long it takes to fill a 1-gallon jug. If it takes 30 seconds: GPM = (1 ÷ 30) × 60 = 2.0 GPM. A 10-minute shower at 2.0 GPM = 20 gallons. Switching from a 3.5 GPM to 1.75 GPM head saves about 5,000 gallons per year.