Enter the volume of fluid and the time it takes to flow to determine the flow rate in liters per second. This calculator helps in measuring the rate of fluid flow in a given time frame.
Liters Per Second Formula
The core volumetric flow rate equation is:
Q = V / t
Where Q is the flow rate in liters per second (L/s), V is the volume of fluid in liters, and t is the elapsed time in seconds. For pipe flow, the equivalent form is Q = A x v, where A is the pipe cross-sectional area (m2) and v is the mean fluid velocity (m/s). Multiply the result by 1,000 to convert m3/s to L/s.
What is a Liter Per Second?
A liter per second (L/s) is a metric unit of volumetric flow rate equal to 0.001 cubic meters per second. It quantifies the volume of fluid passing a fixed point every second. The unit sits in a practical middle ground: large enough for plumbing and fire protection work, yet small enough to describe individual fixture flows. In SI notation the dimension is L3T-1.
L/s is the default flow unit in most national plumbing codes outside North America, including Australian Standard AS/NZS 3500, the European EN 806 series, and South African SANS 10252. HVAC engineers in metric countries size chilled-water and condenser-water piping in L/s, while environmental scientists report stream base flows and stormwater runoff in the same unit.
Common Flow Rate Conversions from L/s
The table below provides exact or rounded conversion factors from 1 L/s to other widely used volumetric flow units.
| Target Unit | Symbol | 1 L/s Equals |
|---|---|---|
| Liters per minute | L/min | 60 |
| Liters per hour | L/h | 3,600 |
| Cubic meters per second | m3/s | 0.001 |
| Cubic meters per hour | m3/h | 3.6 |
| US gallons per minute | GPM | 15.8503 |
| US gallons per hour | GPH | 951.02 |
| Imperial gallons per minute | Imp GPM | 13.1981 |
| Cubic feet per second | cfs | 0.03531 |
| Cubic feet per minute | CFM | 2.1189 |
| Acre-feet per day | ac-ft/d | 0.07016 |
To reverse any conversion, divide by the factor. For example, 100 GPM / 15.8503 = 6.309 L/s.
Real-World Flow Rates in Liters Per Second
Flow rates span many orders of magnitude. The reference table below places common sources on a single L/s scale so users can contextualize calculator results against familiar benchmarks.
| Source / Application | Typical Flow (L/s) | Notes |
|---|---|---|
| Medical IV drip (maintenance) | 0.001 to 0.003 | Roughly 80 to 250 mL/h for adult patients |
| Bathroom faucet | 0.10 to 0.13 | US EPA WaterSense limit is 1.5 GPM |
| Low-flow showerhead | 0.13 to 0.16 | 2.0 to 2.5 GPM; mandated max in many jurisdictions |
| Kitchen faucet | 0.13 to 0.19 | Standard US max is 2.2 GPM (0.14 L/s) |
| Standard showerhead | 0.16 to 0.19 | US federal max 2.5 GPM since 1992 Energy Policy Act |
| Garden hose (1/2 in, 40 psi) | 0.32 to 0.50 | Flow varies sharply with hose length and diameter |
| Washing machine fill | 0.25 to 0.38 | 4 to 6 GPM during fill cycle |
| Residential sprinkler (NFPA 13D) | 0.53 | Minimum design flow: 8 GPM per head |
| Whole-house supply (3/4 in main) | 0.63 to 1.26 | 10 to 20 GPM typical peak demand |
| Swimming pool pump | 1.26 to 3.15 | 20 to 50 GPM; sized for 6 to 8 hour turnover |
| Commercial fire sprinkler riser | 6.3 to 31.5 | 100 to 500 GPM per NFPA 13 |
| Fire hydrant (residual 20 psi) | 63 to 315 | 1,000 to 5,000 GPM depending on main size |
| Small stream base flow | 10 to 100 | Varies seasonally; measured at gauging stations |
| Amazon River at mouth | ~209,000,000 | Average discharge about 209,000 m3/s |
Pipe Diameter and L/s: Design Velocity Approach
Engineers size pipes by selecting a velocity that balances energy cost against pipe material cost. For water at ambient temperature, recommended design velocities range from 0.6 m/s (low-noise residential lines) to 3.0 m/s (short industrial headers).
| Nominal Pipe (DN) | Inside Dia. (mm) | L/s at 1.0 m/s | L/s at 1.5 m/s | L/s at 2.5 m/s |
|---|---|---|---|---|
| DN15 (1/2 in) | 16 | 0.20 | 0.30 | 0.50 |
| DN20 (3/4 in) | 21 | 0.35 | 0.52 | 0.87 |
| DN25 (1 in) | 27 | 0.57 | 0.86 | 1.43 |
| DN32 (1-1/4 in) | 35 | 0.96 | 1.44 | 2.41 |
| DN40 (1-1/2 in) | 41 | 1.32 | 1.98 | 3.30 |
| DN50 (2 in) | 53 | 2.21 | 3.31 | 5.52 |
| DN80 (3 in) | 78 | 4.78 | 7.16 | 11.94 |
| DN100 (4 in) | 102 | 8.17 | 12.25 | 20.42 |
| DN150 (6 in) | 154 | 18.63 | 27.94 | 46.57 |
| DN200 (8 in) | 203 | 32.35 | 48.52 | 80.87 |
Values are calculated from Q = (pi/4)(D/1000)2 x v x 1000. Actual inside diameters vary by pipe schedule and material (copper, PVC, steel), so confirm dimensions from manufacturer tables for real projects.
Laminar vs. Turbulent Flow and the Reynolds Number
Whether a flow in a pipe is smooth (laminar) or chaotic (turbulent) depends on the Reynolds number, Re = v x D / nu, where nu is kinematic viscosity (about 1.004 x 10-6 m2/s for water at 20 C). For internal pipe flow, Re below 2,300 indicates laminar conditions, Re above 4,000 indicates fully turbulent flow, and the range between is a transition zone.
In practice, almost all plumbing and HVAC water flows are turbulent. A DN25 pipe carrying just 0.2 L/s of room-temperature water already reaches Re of about 9,400, well into the turbulent regime. Laminar water flow in pipes only occurs at very low velocities or in high-viscosity fluids like heavy oils and syrups.
L/s in Industry Standards
Different industries reference L/s in their codes and design guidelines. Plumbing codes such as Australia’s AS/NZS 3500.1 assign probable simultaneous flow in L/s to each fixture type (a basin is 0.03 L/s, a shower valve is 0.15 L/s, a water closet flush valve is 1.5 L/s) and use probability methods to size supply pipes. HVAC designers convert cooling loads to chilled-water flow via Q(L/s) = load(kW) / (4.18 x delta-T), where 4.18 kJ/(kg*K) is the specific heat of water. Fire protection engineers calculate sprinkler demand in L/s using Q = A x density. Environmental regulators set minimum environmental flows for rivers in L/s or ML/d (megaliters per day; 1 ML/d = 11.574 L/s).
Frequently Asked Questions
How many GPM is 1 L/s?
1 liter per second equals 15.8503 US gallons per minute. This conversion is one of the most used in cross-referencing metric and imperial plumbing specifications.
How do I convert L/min to L/s?
Divide liters per minute by 60. For example, 120 L/min / 60 = 2.0 L/s.
What L/s flow rate does a typical household need?
Peak instantaneous demand for a 2-bathroom home is roughly 0.5 to 0.75 L/s. Homes with multiple simultaneous fixtures (irrigation, washing machine, two showers) can peak near 1.0 to 1.5 L/s.
Is L/s the same as kg/s for water?
Nearly. At 4 C, water density is exactly 1 kg/L, so L/s and kg/s are identical. At 20 C density drops to about 0.998 kg/L, making the difference negligible for most engineering purposes. For other fluids the density must be accounted for: mass flow = volumetric flow x density.
Why does my measured flow differ from the calculator result?
The basic formula Q = V/t assumes steady-state flow. Real systems have pressure fluctuations, pipe friction losses, fittings, and elevation changes that affect instantaneous flow. The pipe and rainfall tabs on the calculator above account for some of these factors, but field measurements with a flow meter or timed bucket test remain the most reliable method for verifying actual rates.
