Flow Rate Calculator

What is Volumetric Flow Rate?

Volumetric flow rate (Q) measures how much fluid passes through a cross-section per unit time. Expressed in m³/s, L/s, L/min, GPM, or CFM, it is fundamental to pipe sizing, pump selection, and fluid system design.

The Flow Rate Formula

Q = A × v

Where:

• Q = volumetric flow rate (m³/s)
• A = cross-sectional area of the pipe (m²) = π × (D/2)²
• v = average fluid velocity (m/s)

How to Use This Calculator

Enter pipe diameter and fluid velocity to calculate flow rate. Or enter flow rate and pipe diameter to find velocity. The calculator converts between common units (GPM, L/min, m³/hr).

Practical Examples

Example 1: 50mm diameter pipe, water velocity 2 m/s. A = π × 0.025² = 0.00196 m². Q = 0.00196 × 2 = 3.93 L/s = 236 L/min = 62.3 GPM.

Example 2: Irrigation system requires 100 GPM through a 3-inch pipe. Velocity = 100 × 0.0631 / (π × 0.0381²) = 3.48 m/s — borderline high for a gravity system.

Recommended Velocities

| Application | Recommended Velocity | |-------------|----------------------| | Domestic water supply | 1–2 m/s | | Industrial pipes | 2–3 m/s | | Fire suppression | 3–5 m/s | | Suction lines | 0.5–1.5 m/s |

Why Flow Rate Matters

Correct flow rate calculation is essential for: pipe sizing to avoid excessive pressure drop, pump selection (Q is the key parameter), water treatment plant capacity, HVAC chilled water systems, and irrigation design.