What are Liters per Minute?
The liter per minute (L/min or LPM) is a unit of volumetric flow rate. It tells you how many liters of liquid flow through a pipe, tap, or nozzle in one minute. It is widely used in plumbing, irrigation, industrial fluid systems, and water treatment. Unlike the standard liter per minute (SLPM) — which applies to gases at standard conditions — the plain L/min refers to any liquid.
How to Use the Liters per Minute Calculator
This calculator offers two independent methods for finding the flow rate in L/min:
Method 1 — Volume & Time
The simplest approach: let the liquid flow for a measured period, collect the output, and enter the values.
- Select what to calculate: flow rate, volume, or time.
- Enter the known values (volume and time for flow rate; rate and time for volume; rate and volume for time).
- Choose your preferred units from the dropdowns (liters, US gallons, cubic feet, etc.).
- Click Calculate — the result appears instantly with a full conversion table.
The underlying formula is:
Flow rate (L/min) = Volume (L) ÷ Time (min)
Method 2 — Cross-sectional Area & Velocity
Use this method when you know the pipe or duct dimensions and the fluid velocity.
- Switch to the Area & Velocity mode.
- Choose the cross-section shape: Circle (most common for pipes), Rectangle, or Square.
- Enter the relevant dimension (internal diameter for a circle, width and height for a rectangle, side for a square) and select the unit (mm, cm, m, in, ft).
- Enter the fluid velocity and choose its unit (m/s, ft/s, km/h, etc.).
- Click Calculate to get the volumetric flow rate.
The formula for a circular pipe:
Area = π × (d/2)²Flow rate (L/min) = Area (dm²) × Velocity (dm/min)
Note: 1 liter = 1 dm³, so for consistent results the area must be in dm² and velocity in dm/min.
Optional: Water Cost Estimation
If you know the price of water per cubic meter (m³) in your region, the calculator can also show you the running cost of the flow per minute, hour, and day. Simply enter the price and choose your currency — USD, RUB, EUR, GBP, and 12 other world currencies are available. The ruble (₽) appears right below the dollar as the second currency in the list.
How to Convert Liters per Minute to Other Units
| From L/min | Multiply by | To get |
|---|---|---|
| L/min | ÷ 60 | Liters per second (L/s) |
| L/min | × 60 | Liters per hour (L/h) |
| L/min | ÷ 1,000 × 60 | Cubic meters per hour (m³/h) |
| L/min | ÷ 3.78541 | US gallons per minute (GPM) |
| L/min | ÷ 28.3168 | Cubic feet per minute (CFM) |
Metric vs. American (Imperial) Units
The calculator fully supports both measurement systems:
- Metric: liters, milliliters, cubic centimeters, cubic meters, meters per second, km/h.
- American / Imperial: US gallons, UK gallons, cubic feet, cubic inches, US quarts, US pints, feet per second, feet per minute, mph.
FAQs
How much water can flow through a 6-inch pipe?
A 6-inch (152.4 mm) diameter pipe at a typical flow velocity of 3 ft/s (~0.91 m/s) carries about 998 L/min (264 US GPM). Use the Area & Velocity mode with shape = Circle, diameter = 6 in, velocity = 3 ft/s to verify this instantly.
How do I calculate flow rate through a pipe?
Use the formula: Q = A × v, where Q is the volumetric flow rate, A is the cross-sectional area of the pipe, and v is the average fluid velocity. The Area & Velocity mode does this automatically in any unit combination.
What is the difference between L/min and SLPM?
L/min (liters per minute) is used for liquids and is based on the actual volume passing a point. SLPM (standard liters per minute) is used for gases and is normalized to standard temperature and pressure (0 °C, 101.325 kPa) to allow fair comparison regardless of conditions.
How do I convert GPM to L/min?
Multiply the GPM value by 3.7854. For example, 10 GPM × 3.7854 = 37.85 L/min. The calculator shows all conversions automatically in the results table.
What is a typical shower flow rate in L/min?
Standard shower heads flow at 6–9 L/min (1.5–2.5 GPM). Water-saving models drop to 4–6 L/min. High-pressure rain showers can reach 15–20 L/min.