Calculate liters per second from volume and time or pipe diameter and velocity, or solve for volume, time, diameter, or velocity with common units.
Liters Per Second Formula
The core volumetric flow rate equation is:
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 used in metric plumbing and hydraulic work. The applicable standard, edition and local requirements determine how design flows are selected. 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 | 13.1982 |
| Cubic feet per second | cfs | 0.03531 |
| Cubic feet per minute | CFM | 2.1189 |
| Acre-feet per day | ac-ft/d | 0.07005 |
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 examples below give a sense of scale; they are not clinical recommendations, sprinkler design minima, or predictions for a particular installation. Fixture certification criteria and federal limits are labeled separately.
| Source / Application | Illustrative Flow or Stated Limit (L/s) | Notes |
|---|---|---|
| Metered-fluid conversion example | 0.00002222 to 0.00006944 | 80 to 250 mL/h converted to L/s; not medical dosing guidance |
| WaterSense bathroom faucet criterion | Maximum 0.09464 | 1.5 US GPM at 60 psi; voluntary EPA certification criterion |
| WaterSense showerhead criterion | Maximum 0.12618 | 2.0 US GPM; voluntary EPA certification criterion |
| Covered faucet federal limit | Maximum 0.13880 | 2.2 US GPM at 60 psi under 10 CFR 430.32(o) |
| Covered showerhead federal limit | Maximum 0.15773 | 2.5 US GPM at 80 psi under 10 CFR 430.32(p) |
| 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 |
| Sprinkler flow conversion example | 0.50472 | 8 US GPM example only. Required flow depends on listing, pressure and coverage; this is not a universal NFPA minimum |
| 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 |
| Large flow conversion example | 6.3 to 31.5 | 100 to 500 US GPM, rounded; not an NFPA 13 design requirement |
| 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 |
| Large-river-scale conversion example | 209,000,000 | 209,000 m3/s converted to L/s; illustrative scale, not a current measured discharge |
Pipe Diameter and L/s: Design Velocity Approach
Engineers size pipes by selecting a velocity that balances energy cost against pipe material cost. The velocities in the following table are calculation scenarios, not universal design recommendations. Appropriate velocity depends on the system, noise, erosion, pressure losses and applicable requirements.
| 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 | 7.17 | 11.95 |
| DN100 (4 in) | 102 | 8.17 | 12.26 | 20.43 |
| DN150 (6 in) | 154 | 18.63 | 27.94 | 46.57 |
| DN200 (8 in) | 203 | 32.37 | 48.55 | 80.91 |
Values are calculated from Q = (pi/4)(D/1000)2 x v x 1000. The inside diameters shown are illustrative inputs, not a pipe-dimension standard. 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 internal flow occurs at sufficiently low Reynolds number; velocity, diameter and fluid viscosity all affect that number.
L/s in Industry Standards
Different industries reference L/s in their codes and design guidelines. Plumbing standards use fixture demand and simultaneous-use methods to select design flow; consult the applicable edition rather than treating example flows as universal allowances. For an approximate chilled-water calculation, Q(L/s) = load(kW) / [rho(kg/L) x c_p(kJ/(kg*K)) x delta-T(K)]. Using 4.18 for c_p also requires a density assumption; the common shortcut assumes rho approximately 1 kg/L. Sprinkler design must follow the applicable listing, coverage and discharge requirements. 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?
There is no single required flow for every household. Fixture ratings, simultaneous use, irrigation and applicable plumbing requirements determine the demand. This calculator converts a specified or measured flow; it does not size a household supply.
Is L/s the same as kg/s for water?
Nearly. Near 4 °C, water density is approximately 1 kg/L, so L/s and kg/s are numerically close rather than exactly 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 measured formula Q = V/t gives average flow over the timed interval, even when instantaneous flow varies. The pipe modes use a full circular cross-section and mean velocity. They do not model rainfall, pressure, friction, fittings or elevation. Use appropriate field measurements to check actual rates.
