Viscometry Relative Viscosity Calculator

Compute relative viscosity (η_rel) from flow time measurements of a polymer solution and solvent. Designed for students, researchers, and technicians working with Ostwald or Ubbelohde viscometers. Handles seconds (s) and minutes (min). Fully offline—no data leaves your browser.

Educational only. Follow your lab SOPs and SDS. Never pipette by mouth.

Flow Time Measurements

Solvent Flow Time (t₀)

Enter time for pure solvent to pass between viscometer marks.

Solution Flow Time (t)

Enter time for polymer solution (same viscometer).

Apply density correction (η_rel = (tρ)/(t₀ρ₀))

Enable if solution and solvent densities differ significantly.

Result Decimal Places

Relative Viscosity Result

Relative Viscosity (η_rel):

1.500

Unitless ratio (dimensionless).

Intermediate Values & Checks

Flow time ratio (t/t₀): 1.500
Density ratio (ρ/ρ₀): 1.000 (correction not applied)
All times in consistent units (seconds).

Understanding Relative Viscosity in Polymer Solutions

Relative viscosity (η_rel) is a fundamental parameter in polymer chemistry, indicating how much a polymer solution retards flow compared to the pure solvent. It's the first step in determining intrinsic viscosity [η], which relates to polymer molecular weight via the Mark–Houwink–Sakurada equation.

Step‑by‑Step Usage

Measure flow time of pure solvent (t₀) in a clean, calibrated viscometer (e.g., Cannon‑Ubbelohde) at constant temperature.
Measure flow time of the polymer solution (t) at identical conditions.
Enter both times in the calculator. Use the same unit for both.
If solution density differs from solvent by >1%, enable density correction and enter densities (typically from a pycnometer).
Read η_rel = (t × ρ) / (t₀ × ρ₀). If density correction is off, η_rel = t / t₀.

Real‑World Examples

Scenario	t₀ (s)	t (s)	ρ₀ (g/mL)	ρ (g/mL)	η_rel
Polystyrene in toluene (dilute)	120.5	145.2	0.867	0.868	1.205
PEG in water (5% w/v)	100.0	115.5	0.998	1.010	1.169
High‑conc. cellulose in DMAc	85.3	210.7	0.944	0.950	2.481

Common Mistakes Checklist

Not thermostatting the viscometer bath (±0.1°C drift can cause >1% error).
Using different viscometers for solvent and solution.
Ignoring density correction for concentrated solutions (>2% w/v).
Not filtering solutions to remove dust or gel particles.
Recording flow times with insufficient precision (use stopwatch with 0.1s resolution).

Frequently Asked Questions

What accuracy can I expect from this calculation?

The calculation is exact for your inputs. Experimental accuracy depends on temperature control, timing precision, and viscometer cleanliness. Typical relative uncertainty is 0.5–2%.

When is the density correction necessary?

For dilute solutions (<1% w/v), density correction is often negligible. For concentrated solutions, ionic liquids, or high‑molecular‑weight polymers, measure densities. The correction factor is (ρ/ρ₀).

My relative viscosity is below 1. Is that possible?

No, η_rel should always be ≥1 for polymer solutions. A value <1 indicates measurement error, solvent contamination, or that the "solution" is actually less viscous than the pure solvent (check your inputs).

What viscometer types are supported?

The calculation works for any capillary viscometer (Ostwald, Ubbelohde, Cannon‑Fenske) as long as flow times are measured under identical conditions. The tool does not account for kinetic‑energy or end‑effect corrections.

Safety notes for viscometry?

Wear gloves and safety glasses when handling solvents. Use fume hoods for volatile or toxic solvents. Never force‑dry viscometers with compressed air—rinse with appropriate solvent and air‑dry vertically.

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Viscometry Relative Viscosity Calculator

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