Science · Fluid Mechanics / Engineering

Flow Rate Calculator

Pick what to solve, fill in the rest, and Q = A·v converts between volumetric flow, pipe area and velocity — pipe diameter is handled automatically.

Q = A·v    A = πd²/4
Solve for:
Q · flow rate
d · diameter
v · velocity
Area comes from the diameter: A = πd²/4. For a non-circular duct use the hydraulic diameter.
Solved value
Q—
Continuity equation
Q = A·v
The volumetric flow rate Q is the product of the pipe cross-sectional area A and the average flow velocity v. The area of a circular pipe is A = πd²/4, so Q = πd²v/4. For an incompressible fluid, Q is conserved along a pipe: if the pipe narrows, the velocity must rise to keep the same flow rate.

🔢 Three-way solver

Solve for flow rate, velocity or pipe diameter — just pick the unknown.

📏 Diameter to area

No need to compute πd²/4 yourself — the area is derived automatically.

🔩 Units

L/s, m³/s, m³/h, gpm and mm, cm, m, in all convert.

📈 Worked steps

See the area and the substituted equation, step by step.

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