Tubing Flow Rate Calculator
Calculate volumetric liquid flow based on inner diameter and velocity.
mm
inch
cm
Measure the hole, not the outer wall.
m/s
ft/s
mph
Speed of fluid moving through the tube.
Calculation Results
Litres per Minute:
–
Gallons (US) per Minute:
–
Litres per Hour:
–
Cubic Meters per Hour:
–
Cross-Sectional Area: – mm²
Understanding Tubing Flow Rates
Accurately calculating the flow rate of fluid through tubing is essential for various applications, ranging from aquarium plumbing and hydroponics to medical IV drips and industrial hydraulic systems. The flow rate determines how much volume of liquid is transported over a specific period.
The Flow Rate Formula
The volumetric flow rate ($Q$) is calculated based on the cross-sectional area of the tubing ($A$) and the average velocity of the fluid ($v$). The fundamental equation used in this calculator is:
$$Q = A \times v$$
Where:
- Q is the volumetric flow rate (e.g., Litres per Minute).
- A is the cross-sectional area of the tube's inner space.
- v is the velocity at which the fluid travels.
Why Inner Diameter (ID) Matters
When selecting tubing (e.g., PVC, silicone, or copper), manufacturers often list both Outer Diameter (OD) and Inner Diameter (ID). You must always use the Inner Diameter for flow calculations. The wall thickness of the tubing reduces the available area for fluid flow. Using the OD will result in a gross overestimation of your system's capacity.
The area is derived from the ID using the circle area formula: $A = \pi \times (ID/2)^2$.
Typical Velocity Ranges
If you aren't sure what velocity to input, here are common standards:
- Gravity Flow (low pressure): 0.5 to 1.5 m/s
- Suction Lines (Pump inlet): 0.6 to 1.2 m/s (to prevent cavitation)
- Pressure Lines (Pump outlet): 1.5 to 3.0 m/s
- Industrial Water Supply: 1.0 to 2.5 m/s
Example Calculation
Imagine you have a standard 1/2 inch (12.7mm) ID tubing and the water is being pumped at a velocity of 2 meters per second.
- First, calculate the radius: $12.7mm / 2 = 6.35mm$.
- Convert to meters: $0.00635m$.
- Calculate Area: $\pi \times 0.00635^2 \approx 0.0001267 m^2$.
- Calculate Flow: $0.0001267 m^2 \times 2 m/s = 0.0002534 m^3/s$.
- Convert to Litres per Minute: $0.0002534 \times 60,000 \approx 15.2 LPM$.