GPM Calculator
Flow rate in GPM two ways. Click any i for detail.
Flow
Method
i
Mode
Bucket test or pipe velocity. |
|
|---|---|
Gallons collected
i
Gallons
Bucket or meter volume. |
|
Seconds
i
Time
How long to collect that volume. |
|
Inner diameter (in)
i
ID
Pipe inside diameter. |
|
Velocity (ft/s)
i
Velocity
Average flow speed. |
How to use this calculator
- Pick bucket test (volume over time) or pipe diameter × velocity.
- Enter the measured gallons and seconds, or pipe ID and ft/s.
- Read gallons per minute and liters per minute.
- Use bucket mode for fixtures when you can catch flow.
Results explained
GPM is standard for wells, irrigation, and plumbing specs. The pipe formula assumes circular section and water-like flow.
Quick reference: GPM
5 gallons in 20 seconds is 15 GPM.
| Item | Detail |
|---|---|
| Bucket | GPM = (gallons / seconds) × 60 |
| Pipe (approx) | GPM ≈ 2.45 × velocity(ft/s) × ID(in)² |
| 15 GPM | common residential well target band |
| CFM | airflow uses cubic feet per minute, not GPM |
Viscosity and turbulence are not modeled on the pipe path.
How the estimate is built
bucket: GPM = gal/sec × 60; pipe: GPM ≈ 2.45·v·d².
Example scenario
5 gal in 20 s → 15 GPM.
FAQ
Which method is more accurate?
Bucket test measures what you actually captured. Pipe math is a textbook estimate.
Can I use this for pool fill time?
Divide pool volume by GPM for a rough hours estimate; volume pages give gallons from dimensions.
Why liters per minute too?
Metric specs often list L/min on pump labels.