Siphon Flow Rate Calculator
Millimeters (mm)
Centimeters (cm)
Inches (in)
Meters (m)
Centimeters (cm)
Feet (ft)
Inches (in)
This is the vertical distance between the source liquid surface and the tube outlet.
Meters (m)
Centimeters (cm)
Feet (ft)
Inches (in)
Estimated Flow Rate
Flow Velocity:
0 m/s
Liters per Minute:
0 LPM
Gallons per Minute (US):
0 GPM
Liters per Hour:
0 LPH
*Calculation assumes a standard smooth pipe (PVC/hose) with a friction factor of ~0.02 and considers minor losses for entrance and exit. Actual flow may vary based on temperature, fluid viscosity, and bends in the tubing.
What is Siphon Flow?
A siphon is a continuous tube that allows liquid to drain from a reservoir through an intermediate point that is higher than the reservoir itself, driven by hydrostatic pressure and gravity. The flow occurs because the outlet of the tube is lower than the liquid surface in the source container.
Once the tube is primed (filled completely with liquid), the force of gravity pulling down on the taller column of liquid on the discharge side causes a pressure drop at the highest point, effectively "pulling" the liquid up and over the crest.
How the Siphon Flow Rate Calculator Works
This calculator estimates the volumetric flow rate of a liquid through a siphon based on the Bernoulli equation, adjusted for head loss due to friction and entrance/exit effects. It is particularly useful for aquariums, home brewing, drainage, and irrigation systems.
The Physics Formula
To calculate the velocity ($v$) of the fluid, we use a modified energy equation that balances potential energy with kinetic energy and friction losses:
v = √ [ (2 · g · h) / (1 + K + f · (L / D)) ]
Where:
- g: Acceleration due to gravity (9.81 m/s²)
- h: Head height (elevation difference between source surface and outlet)
- L: Total length of the pipe
- D: Internal diameter of the pipe
- f: Friction factor (estimated at 0.02 for smooth plastic tubing)
- K: Minor loss coefficient (approx 1.5 for entrance and exit losses)
Once velocity is found, the Flow Rate ($Q$) is calculated as:
Q = Area × Velocity = (π · (D/2)²) × v
Factors Affecting Siphon Performance
| Factor | Impact on Flow |
|---|---|
| Head Height (h) | The greater the vertical drop between the water surface and the hose outlet, the faster the flow. If the outlet is level with the surface, flow stops. |
| Pipe Diameter (d) | Diameter has a massive impact. Doubling the diameter can increase flow rate by more than 4 times due to reduced friction relative to volume. |
| Pipe Length (L) | Longer pipes introduce more friction (drag), which slows down the water velocity. Keep hoses as short as possible for maximum speed. |
| Viscosity | Thicker liquids (like syrup or oil) flow much slower than water. This calculator is calibrated for water-like viscosity. |
Common Uses
Aquariums: Calculating how fast a tank will drain during water changes or sump overflow scenarios.
Home Brewing: Estimating transfer times for racking beer or wine between carboys.
Rain Barrels: determining flow rate from a collection barrel to a garden bed via a hose.