Use this chemistry calculator to reproduce a named relationship with explicit quantities and units for study, laboratory planning, or an independent numerical check.

Weight-average molar mass

Required number input.

Number-average molar mass

Required number input.

Calculate polymer dispersity Đ=Mw/Mn from weight-average and number-average molar masses. For a valid nonnegative molecular-weight distribution, Mw should not be below Mn. The tool evaluates the supplied inputs together and returns the named outputs below; it does not infer omitted operating conditions or change the units shown.^[1]

dispersity

The resulting dispersity returned as a number.

• Polymer averages and dispersity depend on the molecular-weight distribution and measurement method. Branching, copolymers, end groups, conversion, degradation, and calibration standards can make ideal chain relationships incomplete.
• Use finite inputs in the displayed units and preserve more precision than the final presentation requires. Independently verify safety-critical, financial, compliance, or production decisions.

Check units and significant figures, compare the result with limiting cases, and use measured or source-specific constants where available. Laboratory, safety, and regulatory decisions require validated methods and appropriate uncertainty analysis.

• Polymer Number-Average Molecular Mass

  Calculate Mn=ΣNiMi/ΣNi from counts of polymer chains in each molar-mass bin. Counts and masses must have equal, nonempty lengths; masses should use a consistent unit.

• Polymer Weight-Average Molecular Mass

  Calculate Mw=ΣNiMi²/ΣNiMi from a polymer chain-count distribution. Heavy chains contribute disproportionately, so Mw is normally at least Mn for the same distribution.

• Number-Average Degree of Polymerization

  Estimate number-average polymerization degree as number-average molecular mass divided by repeat-unit molar mass. Both masses must use the same unit; end-group mass is neglected.