Poiseuille's Law Calculator

Find laminar flow rate through a narrow tube.

Pressure difference (Pa)

Tube radius

Dynamic viscosity (Pa·s)

Tube length

Flow rate (m³/s) 0

Formula: Q = π·ΔP·r⁴ ÷ (8·μ·L)

Step-by-step with your numbers:

1. Values used:

2. Pressure difference = 1,000 Pa

3. Tube radius = 1

4. Dynamic viscosity = 0.001 Pa·s

5. Tube length = 0.1

7. Flow rate = 0m³/s

Did we solve your problem today?

Poiseuille's law governs slow, smooth flow through narrow tubes — like blood in vessels.

The math behind it

Q = π·ΔP·r⁴ ÷ (8·μ·L). The r⁴ term means tiny radius changes hugely affect flow.

ΔP 1000 Pa, r 1 mm, water, 0.1 m → about 3.93 × 10⁻⁶ m³/s.

Why is radius so important?

Flow scales with r⁴, so halving the radius cuts flow to one-sixteenth.