Calculator
Pick a method, enter values with units, then calculate. The form uses responsive columns: 3 on large screens, 2 on small, 1 on mobile.
Example Data
These examples show typical inputs and outputs. Values are illustrative.
| Method | Sample inputs | Output (approx.) |
|---|---|---|
| Shear stress / gradient | τ = 50 Pa, du/dy = 500 1/s | μ ≈ 0.1 Pa·s (100 cP) |
| Force / gap | F = 2 N, A = 0.02 m², V = 0.5 m/s, h = 1 mm | μ ≈ 0.2 Pa·s (200 cP) |
| Density × kinematic | ρ = 998 kg/m³, ν = 1 cSt | μ ≈ 0.000998 Pa·s (0.998 cP) |
| Laminar pipe flow | ΔP = 10 kPa, L = 2 m, Q = 1 L/min, D = 10 mm | μ ≈ 0.49 Pa·s (490 cP) |
Formula Used
- μ = τ / (du/dy) using Newton’s law of viscosity.
- μ = F·h / (A·V) from τ = F/A and shear rate ≈ V/h.
- μ = ρ·ν linking dynamic and kinematic viscosity.
- μ = (π·r⁴·ΔP) / (8·Q·L) for laminar pipe flow, with r = D/2.
Output units: Pa·s, mPa·s, cP, and P. Note: 1 cP = 1 mPa·s and 1 P = 0.1 Pa·s.
How to Use This Calculator
- Select the method that matches your measurements.
- Enter each value and choose its unit from the dropdown.
- Press Calculate to see results above the form.
- Review the SI-converted inputs for quick verification.
- Use the download buttons to export CSV or PDF reports.
FAQs
1) What is dynamic viscosity?
Dynamic viscosity (μ) measures how strongly a fluid resists shear flow. Higher μ means thicker, slower-flowing behavior, like honey compared to water.
2) What units are most common?
SI uses Pa·s. Many lab and industry references use cP (centipoise) or mPa·s. They are numerically equal: 1 cP = 1 mPa·s.
3) When should I use τ divided by du/dy?
Use it when you have shear stress and velocity gradient from experiments, rheometers, or simulations. It directly follows Newton’s law for Newtonian fluids.
4) How does density relate to viscosity?
Kinematic viscosity ν describes momentum diffusion and equals μ/ρ. If you know density and ν, multiply them to obtain μ in Pa·s.
5) Is the pipe-flow method always valid?
No. The Hagen–Poiseuille equation assumes steady, incompressible, fully developed laminar flow of a Newtonian fluid in a straight circular pipe.
6) What is a good laminar threshold?
In many cases, laminar flow in pipes is expected for Reynolds number below about 2000. The optional density input lets the calculator estimate Reynolds.
7) Why do my results look too large or small?
Unit mismatches cause most issues. Confirm pressure, length, and flow units, and check that denominators like velocity, gradient, and area are not near zero.
8) Does this work for non-Newtonian fluids?
The formulas assume Newtonian behavior where μ is constant. For non-Newtonian fluids, μ changes with shear rate, so you must use rheology models and measured curves.