Measure flow rate with a bucket fill-time test, convert GPM to and from L/min, m³/h, GPH, CFS and L/s, plan fill times, and estimate well pump drawdown — imperial and metric, 100% in your browser.
This page is the GPM-centered flow rate tool: every calculation starts from or ends at gallons per minute, the unit used for well yield tests, pump ratings, and plumbing fixtures in the US.
Time how long it takes to fill a container of known size. GPM = gallons ÷ (seconds ÷ 60). The 5 gallon bucket gpm test is the classic field method for well yield tests and checking pump output — this bucket test gpm calculator automates the math.
Enter a flow rate in any unit — the converter shows all six. It works as a gpm to liters per minute converter, a gpm to m3/h converter, a gpm to cfs calculator, an l/min to gpm converter, and a gph to gpm converter: just change the input unit. Exact definitions: 1 US gallon = 3.785411784 L; 1 ft³/s = 448.8311688 GPM.
Given a target flow rate in GPM, how long to fill a volume? Use it as a pool fill time calculator gpm planner for pools, tanks, and cisterns.
Balances pump withdrawal against aquifer recovery. Net drawdown = pump GPM − recovery GPM.
Planning values compiled from US federal standards (Energy Policy Act of 1992), EPA WaterSense specifications, and common irrigation practice. Treat ranges as typical, not guarantees — actual flow depends on pressure and hardware. Typical irrigation gpm requirements are listed in the table below.
| Fixture | GPM | L/min | Basis / note |
|---|---|---|---|
| Shower (federal max, EPAct 1992) | 2.50 | 9.46 | US federal maximum |
| Shower (WaterSense) | 2.00 | 7.57 | EPA WaterSense limit |
| Bathroom faucet (federal max) | 2.20 | 8.33 | US federal maximum |
| Bathroom faucet (WaterSense) | 1.50 | 5.68 | EPA WaterSense limit |
| Kitchen faucet | 2.20 | 8.33 | Typical |
| Toilet | — | — | 1.6 gallons per flush (EPAct 1992) - per flush, not a flow rate |
| Dishwasher (while filling) | 2.00 | 7.57 | Typical |
| Washing machine (while filling) | 4.50 | 17.03 | Typical range 4-5 |
| Garden hose (5/8-3/4 in) | 7.50 | 28.39 | Typical range 5-10 |
| Component | Typical flow | L/min | Note |
|---|---|---|---|
| Spray head | 1.000–3.000 | 3.79–11.36 | Per head |
| Gear rotor | 2.000–5.000 | 7.57–18.93 | Per head |
| Drip emitter | 0.008–0.033 | 0.03–0.13 | Per emitter, in GPH (0.5-2 gal/hour) |
| Yield | GPM | Guidance |
|---|---|---|
| Below 3 | Below 3 | Very low - storage tank usually required |
| 3-5 | 3-5 | Marginal - common minimum lenders look for, sustained |
| 5-10 | 5-10 | Adequate for most homes with a pressure/storage tank |
| 10-20 | 10-20 | Good - comfortably serves a household |
| Above 20 | Above 20 | Excellent |
Bucket method: GPM = gallons / (seconds / 60). A 5-gallon bucket filled in 40 seconds is 5 / (40/60) = 7.5 GPM. In short, how to calculate gpm is always volume divided by time, with the time converted to minutes.
Unit definitions (exact): 1 US gallon = 3.785411784 L. Therefore 1 GPM = 3.785411784 L/min = 0.2271245 m³/h = 60 GPH = 0.0630902 L/s. One cubic foot holds 1728/231 gallons, so 1 ft³/s = 448.8311688 GPM, and 1 GPM = 6.30901964×10⁻⁵ m³/s.
Fill time: minutes = gallons / GPM.
Drawdown: net GPM = pump GPM − recovery GPM; minutes to empty = reserve gallons / net GPM; refill minutes = reserve gallons / recovery GPM. If recovery meets or exceeds pumping, the well is sustainable at that rate.
All displayed values use half-up rounding, identical in the page script and the offline test oracle.
Time how long it takes to fill a container of known size, then divide: GPM equals gallons divided by (seconds divided by 60). A classic 5-gallon bucket that fills in 40 seconds gives 5 / (40 / 60) = 7.5 GPM. Use the bucket test tab above with the 5-gallon preset for well yield tests and pump output checks.
One US gallon per minute equals exactly 3.7854 liters per minute, because one US gallon is defined as 3.785411784 liters. Going the other way, 10 L/min divided by 3.785411784 gives 2.6417 GPM. The converter tab above does this both ways for all six units.
Divide GPM by 448.8311688: one cubic foot per second equals 448.8312 gallons per minute, since a cubic foot holds 1728/231 gallons. So 100 GPM is 100 / 448.8311688 = 0.2228 CFS. This gallons per minute to cubic feet per second conversion is exact by definition. CFS is the standard unit in hydrology and open-channel flow; GPM is standard for pumps, wells, and plumbing.
Divide the pool volume in gallons by the flow rate: a 20,000-gallon pool filling at 8 GPM takes 20,000 / 8 = 2,500 minutes, which is 1 day 17 hours 40 minutes. Enter any volume and target GPM in the fill-time tab above — your pool fill time calculator gpm planner — to plan around pump schedules and water delivery windows.
As typical guidance: below 3 GPM is very low yield, 3-5 GPM is marginal (many lenders look for at least 3-5 GPM sustained), 5-10 GPM is adequate for most homes with a storage tank, 10-20 GPM is good, and above 20 GPM is excellent. Run a well yield gpm test with the bucket tab above before sizing a pump, then use the drawdown estimator to check whether your pump outruns your well's recovery.
Pump a known volume and time it: recovery rate in GPM equals gallons pumped divided by minutes. A basic well recovery rate calculator stops there; the drawdown estimator on this page goes one step further and balances your pump's withdrawal rate against the recovery rate to estimate time-to-empty and refill time. The dedicated well volume calculator covers casing volume, purge, and chlorination with its own recovery-rate tab for simple gal/min timing.
Add up the fixtures that may run at once. Typical flows: shower 2.5 GPM, bathroom faucet 2.2 GPM, kitchen faucet 2.2 GPM, dishwasher about 2 GPM while filling, washing machine 4-5 GPM while filling. A shower plus a faucet plus a dishwasher running together is roughly 2.5 + 2.2 + 2.0 = 6.7 GPM of peak demand. Size the well pump and pressure tank for that peak, not the average — the fixture table below lists every value in GPM and L/min.
No. GPM measures volume flow rate (how much water moves), PSI measures pressure (how hard it pushes). A garden hose can show high PSI with the nozzle nearly closed while flowing almost zero GPM. The gpm vs psi difference trips up many buyers: pressure tells you how hard water pushes, flow tells you how much arrives. Converting a measured pressure drop into a flow rate needs the orifice equation, which is a different calculation — see the PSI to GPM calculator for that pressure-based method.
US federal law (Energy Policy Act of 1992) caps showerheads at 2.5 GPM, and EPA WaterSense models use 2.0 GPM or less. An 8-minute shower at the federal maximum uses 2.5 x 8 = 20 gallons of water. Low-flow heads meeting the WaterSense limit cut that to 16 gallons for the same shower length.
Typical planning values: spray heads 1-3 GPM each, gear rotors 2-5 GPM each, and drip emitters 0.5-2 gallons per hour (note: per hour, not per minute). Size each irrigation zone so the total head demand stays under your available GPM at working pressure; the reference table below lists common values in both GPM and L/min.
Drawdown is what happens when the pump withdraws water faster than the well recovers: net drawdown equals pump GPM minus recovery GPM. Example: a 10 GPM pump on a well recovering at 4 GPM draws down at 6 GPM net, so a 500-gallon usable reserve lasts 500 / 6 = 83.33 minutes, and refills in 500 / 4 = 125 minutes after the pump stops. This is a simplified planning estimate, not a substitute for a professional pump test.
When you know pipe diameter and water velocity and need the flow that results, use the Q = A x v physics solver in the flow rate calculator, which also covers mass flow. This page is the GPM-centered tool: bucket tests, GPM unit conversion, fill-time planning, and drawdown estimates. For sizing the pump itself (horsepower, head, wire-to-water efficiency), use the pump horsepower calculator.