Liters per Minute Calculator

Liters per Minute Calculator finds water flow from a bucket test, pipe bore, pump or nozzle, corrects gas flow to normal L/min, and gives mL/min, L/h, GPM, m³/h and tank fill time.

Using the Liters per Minute Calculator

The Liters per Minute Calculator works from whatever you can measure. The Calculate From box offers eight starting points, from a timed bucket fill and a flow in another unit to pipe size, pipe velocity, pump data, nozzle pressure and gas line readings. Each choice shows only the inputs that method needs.

Volume and Time is the default and matches how most people measure water flow at a tap, hose or well. Convert a Flow Unit takes a reading in L/h, L/s, mL/min, mL/h, m³/h, m³/s, GPM, GPH, UK gpm or CFM and turns it into L/min. Pipe, velocity, pump, nozzle and gas readings each have their own method, so you never convert by hand first.

The closed Tank and Run Time panel holds a tank volume and a run time, set to 1,000 L and 15 minutes by default. Every water method uses them to show how long the tank takes to fill and how much water a run delivers. Change them to match your own tank, pool zone or pump cycle.

Liters per Minute Formula

Flow rate is volume divided by time, and the Liters per Minute Calculator applies that rule in every water method. For liters per minute, put the volume in liters and the time in minutes before dividing.

$$Q=\frac{V}{t}$$

The calculator opens on that exact case, a 300 L container filled in 30 minutes, which gives 10 L/min. A bucket test is usually timed in seconds, so multiply by 60 to bring a per-second result up to a per-minute one.

$$Q_{\text{L/min}}=\frac{V_{\text{L}}}{t_{\text{s}}}\times 60$$

A 10 L bucket that fills in 20 seconds gives 0.5 L/s, or 30 L/min. In the Liters per Minute Calculator, enter 10 L and 20 s and the units convert for you, including milliliters, US and UK gallons, cubic feet and hours.

Running a bucket test

Use a container with a known volume that takes at least 10 seconds to fill. Open the tap fully, start timing as the water enters, and stop when it reaches the mark. With other taps closed, the reading reflects the supply rather than the household demand at that moment.

Repeat the test two or three times and use the average. For irrigation design, set Flow Use to Irrigation design (-20%), which cuts the result by a fifth to allow for pressure loss in the system the water will feed. Skip that cut when you tested right at the main feed.

What the Water Results Show

The large box in the Liters per Minute Calculator gives the flow in L/min, with US GPM and L/h underneath. Two cards then restate it in other units. The first covers L/s, mL/min, m³/h, mL/h and m³/s, and the second covers US gallons per hour, UK gallons per minute, CFM and US gallons per day.

For the default 10 L/min, that means 0.167 L/s, 10,000 mL/min and 0.600 m³/h on one card, and 158.5 GPH, 2.20 UK gpm and 0.353 CFM on the other. The All Flow Units panel lists twelve units side by side, and the math panel shows every conversion step.

The third card uses the Tank and Run Time values. At 10 L/min, a 1,000 L tank fills in 1 h 40 min, a 15-minute run delivers 150 L, and a full day of flow adds up to 14.4 m³. The fourth card compares your flow with a standard and a WaterSense showerhead.

Print Results saves the whole result as a PDF. Keep it with a well log, an irrigation plan or a pump service sheet to compare against the next test.

Is 12 L/min a Good Flow?

Flow and pressure are different things. Flow is how much water arrives each minute, while pressure is the push behind it. A fixture can have strong pressure and still deliver low flow if its aerator, a valve or a clogged filter holds it back.

The shower card in the Liters per Minute Calculator compares your flow with two benchmarks. EPA's WaterSense showerhead statement cites the federal maximum of 2.5 GPM set by EPAct 1992, tested at 80 psi, which is 9.46 L/min. WaterSense labeled showerheads use no more than 2.0 GPM, or 7.57 L/min.

So 12 L/min, or 3.17 GPM, is 127 percent of a standard showerhead and 159 percent of a WaterSense one. That supply can run any compliant shower with some to spare. For a whole house, add up the fixtures that run at the same time and compare the total with a bucket test at the main tap.

Liters per Minute Conversions

Every flow conversion is one multiply or divide once you know the liters in the other unit. One US gallon is exactly 3.785411784 L, one imperial gallon is 4.54609 L and one cubic foot is 28.317 L. The Convert a Flow Unit method in the Liters per Minute Calculator applies these for you.

The Convert method opens on 120 L/h, a common drip and dosing pump rating, which comes out at 2 L/min. For work that starts in gallons, the Gallons Per Minute Calculator runs the same tests with GPM as the main result.

mL per Minute and mL per Hour

Small flows from a drip line, a dosing pump or a lab feed read better in milliliters. Divide the milliliters by the minutes for mL/min, then multiply by 60 for mL/h. Going from mL/h back to mL/min is a divide by 60.

A rate of 100 mL in 30 minutes is 3.33 mL/min, or 200 mL/h. A rate of 50 mL over 20 minutes is 2.5 mL/min, or 150 mL/h. Enter either case in the Liters per Minute Calculator under Volume and Time, with mL and min selected, and the first result card shows both mL/min and mL/h.

To convert the other way, pick Convert a Flow Unit and choose mL/min or mL/h in the unit menu. At 1 L/min, one minute delivers 1,000 mL, which is 16.7 mL every second.

Flow From Pipe Size and Velocity

When you know how fast water moves through a pipe, flow equals the inside area times the velocity. With area in m² and velocity in m/s, the result is in m³/s, and multiplying by 60,000 gives L/min.

$$Q=A\times v\times 60000$$

The Pipe Diameter and Velocity method in the Liters per Minute Calculator opens on a 25 mm bore at 1.5 m/s. The area is 4.91 cm², so the flow is 44.2 L/min, or 11.7 GPM. Use the true inside diameter, because nominal sizes and outside diameters both overstate the area.

Both pipe methods warn once velocity passes 8 ft/s (2.44 m/s), the top of the cold-water range below. Hot water should run slower still, but the tool has no temperature input, so check that limit yourself. Entering 3 m/s in the same 25 mm pipe gives 88.4 L/min and trips the warning.

The Water Depth box handles a pipe that runs partly full, such as a drain or culvert. Below 100 percent, the tool uses circle-segment geometry for the wet area and draws the cross-section to scale. At half depth, the same pipe carries 50 percent of the bore area and 22.1 L/min. When a partly full pipe's velocity is unknown, the Partial Pipe Flow Calculator finds both flow and velocity.

The Flow Area card leads with the wet area. For a full pipe it adds the velocity in the other unit and the hydraulic radius, which is d/4. For a partly full pipe it shows the wetted share of the bore and the flow the same pipe would carry running full.

Liters per minute to meters per second

A flow rate has no speed until you choose a pipe, so converting L/min to m/s means dividing by the bore area. The L/min to Pipe Velocity method does this for a pipe running full.

$$v=\frac{Q}{60000\cdot A}$$

It opens on 60 L/min through a 32 mm bore. The area is 8.04 cm², so the water moves at 1.24 m/s, which is 4.08 ft/s or 74.6 m per minute. Enter the diameter in inches and the result switches to ft/s.

The card beside it gives the bore area and the velocity head, v²/2g, which is 78.8 mm here. Multiply the velocity head by a fitting's K value to estimate that fitting's loss.

The Copper Development Association piping guide recommends 5 to 8 ft/s (1.52 to 2.44 m/s) for cold water and 4 to 5 ft/s for hot water below 140°F, to limit erosion. The table shows the flow each bore carries at those two speeds.

Velocity sets the comfort limit, while friction sets how much pressure a long run loses. The Hazen Williams Equation Calculator turns your L/min and bore into a pressure drop, and the Pipe Flow Calculator handles the same velocity math in gallons.

The FPM formula

Feet per minute is the imperial version of the same idea. Divide the flow in cubic feet per minute by the flow area in square feet.

$$\text{FPM}=\frac{\text{CFM}}{A_{{\text{ft}}^2}}$$

For example, 10 L/min is 0.353 CFM, and a 25 mm bore has 0.00528 ft² of area. That gives 67 ft/min, or 1.11 ft/s, the same speed the velocity method returns for 10 L/min in that bore.

Pump Flow in Liters per Minute

How to calculate the LPM of a pump depends on the pump type. The Liters per Minute Calculator has a method for each kind, because a positive displacement pump and a centrifugal pump follow different rules.

RPM to LPM for displacement pumps

A gear, vane or piston pump moves a fixed volume each turn, so its theoretical flow is displacement times speed. With displacement in cc per revolution and speed in rpm, dividing by 1,000 gives L/min.

$$Q=\frac{D\times N}{1000}\times {\eta }_v$$

The Power and Motion pump efficiency guide uses 100 cc/rev at 1,000 rpm for a theoretical 100 L/min. It measures 90 L/min at 207 bar, a volumetric efficiency of 90 percent, and leakage grows as pressure rises. Take that efficiency from the data sheet at your working pressure.

The tool opens on 20 cc/rev at 1,500 rpm, which gives 30 L/min at 100 percent. Its displacement card shows the size in in³/rev, the speed needed for 10 L/min (500 rpm) and the flow per revolution (0.0200 L/rev). Set efficiency below 100 percent and the card shows the theoretical flow and the slip loss to leakage instead.

Flow from pump power and head

A centrifugal water pump has no fixed displacement, and its flow drops as the head it pushes against rises. The maker's pump curve gives the real answer. Without one, the hydraulic power equation estimates flow from motor power P, pump efficiency η and total head H.

$$Q=\frac{\eta \cdot P}{\rho \cdot g\cdot H}$$

The Pump Power and Head method opens on 1.5 hp, 20 m of head and 50 percent efficiency, which gives 171 L/min. A 1.5 hp pump moves less water the higher it has to push it. The table runs the same pump against other heads, keeping efficiency at 50 percent.

Total head is the lift plus pipe friction, so add the friction loss before entering it. The Water Power card shows the 0.75 hp that actually reaches the water, the 342 L/min a perfect pump would move, and the head as pressure, 1.96 bar for 20 m. For head-to-pressure work, the Pump Pressure Calculator goes further.

Liters per Minute to psi for Nozzles

There is no single conversion from L/min to psi, since the link depends on what the water flows through. For a nozzle or sprinkler, flow rises with the square root of pressure, and the K-factor printed on its data sheet ties the two together.

$$Q=K\cdot \sqrt{P}$$

The Nozzle K-Factor and Pressure method takes K in L/min per bar½ or gpm per psi½, and one gpm/psi½ equals 14.4 L/min/bar½. It opens on K 80 at 2 bar, a common sprinkler size, which flows 113 L/min.

The square root makes pressure an expensive way to add flow. Doubling the flow from that nozzle takes 8 bar, four times the pressure, while dropping to 1 bar cuts the flow by 29 percent. The nozzle card shows the pressure needed for double flow, the K-factor in the other unit system and the nozzle pressure in psi.

For a sprinkler system, the Fire Flow Calculator sets the demand, and the nozzle method checks what each head delivers at the pressure you have.

Normal vs Standard Liters per Minute

Normal liters per minute (NLPM) and standard liters per minute (SLPM) are gas units. A liter of compressed gas holds far more gas than a liter at room pressure, so meters restate flow at a fixed reference temperature and pressure.

Flow meter maker Vögtlin defines its references as 0°C and 1,013.25 mbar for normal liters and 20°C at the same pressure for standard liters. It also notes that many European gas suppliers use 15°C. Alicat's pressure and flow explainer lists 0°C to 25°C as common choices, so the label alone never settles the reference.

The Gas Normal L/min method in the Liters per Minute Calculator corrects an actual flow measured at line conditions. It uses absolute pressure and absolute temperature in kelvin.

$$Q_n=Q_a\cdot \frac{P_a}{1.01325}\cdot \frac{273.15}{T}$$

The default is 100 L/min of actual flow at 6 bar gauge (7.01 bar absolute) and 20°C. That equals 645 NL/min, a 6.45 times normal factor, or 692 SL/min at a 20°C reference. Water barely compresses, so liquid flow in liters per minute needs no correction like this.

Quick Answers on L/min

A liter is a volume and a minute is a time, so most flow questions come down to which of the two you know. The answers below use 1 US gallon = 3.785 L and the default 10 L/min flow.

What is litres per minute?

Liters per minute, spelled litres per minute in British English, is the volume of fluid in liters passing a point each minute. It is shortened to L/min or LPM. Faucets, showers, pumps, irrigation zones, wells and oxygen regulators are all commonly rated in L/min.

What is 1 liter equal to?

One liter equals 1,000 mL, 1 cubic decimeter and 0.001 m³. In US units it is 0.264 gallons, 33.8 fluid ounces or 61.0 cubic inches. So 1 mL is not 1 liter, since it takes 1,000 mL to make one liter.

What is LPM capacity?

LPM capacity is the most flow a pump, pipe or fixture can deliver, measured in liters per minute. A pump's capacity comes from its curve at your head, and a pipe's comes from bore area times an acceptable velocity. Storage capacity is a volume instead, which the Tank Volume Calculator finds for nine tank shapes.

How do I calculate total flow rate?

Add the flows of every branch or fixture that runs at the same time. Two 12 L/min irrigation zones and a 9 L/min shower running together need 33 L/min from the supply. Compare that total with a bucket test at the main tap before adding more outlets.

How long will a tank or pool take to fill?

Divide the volume by the flow rate. At 10 L/min, a 1,000 L tank takes 100 minutes, the 1 h 40 min shown on the tank card. For a pool or pond, get the volume from the Pool Calculator or Pond Calculator, then enter it in the Tank Volume box.