LPS (Litres Per Second) Flow Rate Calculator
Calculate volumetric flow rates and pipe discharge speeds instantly.
1. Calculate LPS from Volume and Time
2. Calculate LPS from Pipe Diameter & Velocity
What is an LPS Rate?
LPS stands for Litres Per Second. It is a metric unit of volumetric flow rate used extensively in hydraulics, civil engineering, and plumbing. It represents the volume of fluid (usually water) passing through a specific point or section of a pipe every second.
How to Calculate LPS
There are two primary ways to determine the LPS rate depending on the data you have available:
Method 1: Volume over Time
This is the simplest method. If you know how many litres are discharged over a specific timeframe, the formula is:
LPS = Volume (L) / Time (s)
Method 2: Pipe Cross-Section and Velocity
In engineering, you often know the size of the pipe and the speed of the water. The formula involves the area of the circle (pipe) and the velocity:
- Calculate Area: A = π × (Diameter / 2000)² (to get area in square meters)
- Calculate Cubic Meters per Second: m³/s = Area × Velocity
- Convert to LPS: LPS = m³/s × 1000
If you have a 100mm pipe with water moving at 2 meters per second:
1. Radius = 0.05m
2. Area = 3.14159 × (0.05)² = 0.00785 m²
3. Flow = 0.00785 × 2 = 0.0157 m³/s
4. LPS = 15.7 Litres per second.
Why LPS Rates Matter in Plumbing and Irrigation
Understanding the LPS rate is crucial for ensuring that a system can handle the required load without causing excessive pressure drops or pipe erosion. In domestic settings, low LPS might mean poor shower pressure, while in commercial irrigation, incorrect LPS rates can lead to pump failure or uneven water distribution.
Common LPS Reference Values
- Standard kitchen tap: 0.1 to 0.2 LPS
- Modern shower head: 0.15 to 0.25 LPS
- Fire hydrant: 20 to 50+ LPS
- Main water supply line (Small Town): 100+ LPS
Factors Affecting LPS Rates
Several variables can influence the actual flow rate in a real-world scenario:
- Pipe Friction: Rougher internal surfaces (like old cast iron) slow down velocity.
- Gravity/Head: The height difference between the source and the outlet affects pressure and speed.
- Bends and Valves: Every elbow or valve in a system creates "minor losses," reducing the effective LPS.
- Viscosity: While usually used for water, thicker fluids will flow at lower LPS rates under the same pressure.