Poiseuille's Law Calculator
📐 Physics of Matter. Use the Poiseuille's law formula to find flow rate, pressure drop, pipe radius, viscosity μ, pipe length: pick the value you want, type the others, and the answer updates as you go.
Pick the ○ next to the value you want to find, fill in the others, and it solves as you type.
What each letter means
| Quantity | Unit |
|---|---|
| Flow rate | m³/s |
| Pressure drop | Pa |
| Pipe radius | m |
| Viscosity μ | Pa·s |
| Pipe length | m |
Worked example
Find the flow rate when Pressure drop = 1000 Pa, Pipe radius = 0.002 m, Viscosity μ = 0.001 Pa·s, Pipe length = 1.6 m.
Using Q = (πΔ P r⁴)/(8μ L): Flow rate = 3.927 × 10⁻⁶ m³/s.
Frequently asked questions
What is the formula for Poiseuille's law?
Q = (πΔ P r⁴)/(8μ L).
What do the letters stand for, and what units are used?
Flow rate in m³/s, Pressure drop in Pa, Pipe radius in m, Viscosity μ in Pa·s, Pipe length in m.
How do you calculate flow rate?
Put the values into Q = (πΔ P r⁴)/(8μ L). For example, with Pressure drop = 1000 Pa, Pipe radius = 0.002 m, Viscosity μ = 0.001 Pa·s, Pipe length = 1.6 m, flow rate = 3.927 × 10⁻⁶ m³/s.
Can I solve for a different value?
Yes. In the calculator above, pick the circle next to any value (flow rate, pressure drop, pipe radius, viscosity μ, pipe length) and fill in the others: it rearranges the formula for you.
