Analyze polymer samples with grouped chain entries. See Mn, totals, distribution shares, and polymer metrics. Download CSV and PDF summaries for cleaner lab reporting.
Number average molecular weight: Mn = Σ(Ni × Mi) / ΣNi
Number fraction: xi = Ni / ΣNi
Mass fraction: wi = (Ni × Mi) / Σ(Ni × Mi)
Degree of polymerization: DPn = Mn / M0
Polydispersity index: PDI = Mw / Mn
Ni is chain count or grouped frequency. Mi is molecular weight for that group. M0 is repeat unit molecular weight.
| Group | Molecular Weight, Mi | Chain Count, Ni | Ni × Mi |
|---|---|---|---|
| 1 | 10,000 | 50 | 500,000 |
| 2 | 20,000 | 30 | 600,000 |
| 3 | 40,000 | 20 | 800,000 |
| Totals | 100 | 1,900,000 | |
| Mn = 1,900,000 / 100 = 19,000 g/mol | |||
Number average molecular weight is a core polymer property. It describes the average chain size based on chain count. Every chain contributes equally to the average. A short chain counts once. A long chain also counts once. This makes Mn useful when you study polymerization progress, chain growth, end group analysis, and degradation behavior.
This calculator uses grouped molecular weight data. Each group needs a molecular weight value and a chain count or grouped frequency. The tool multiplies each chain count by its molecular weight. It then sums all weighted values. That total is divided by the total number of chains. The result is Mn. You also get number fraction and mass fraction for each group. These extra values help you inspect the polymer distribution more clearly.
Real polymer samples rarely contain one exact chain length. Most samples contain a distribution. Some chains are light. Others are heavy. Grouped inputs let you model that spread in a simple way. This is useful for lab reports, gel permeation chromatography summaries, teaching examples, and production checks. If you already know the repeat unit molecular weight, the calculator can also estimate the degree of polymerization. That adds more value during material characterization.
Mn is often compared with weight average molecular weight. When both values are available, you can calculate the polydispersity index. That helps you understand distribution breadth. A narrow distribution often supports more controlled behavior. A broad distribution may change processing and performance. Use this page to calculate Mn quickly, compare batches, export clean results, and document polymer averages with less manual work.
It is the total weighted molecular mass divided by total chain count. Each polymer chain contributes equally, regardless of how large or small it is.
Use Mn = Σ(Ni × Mi) / ΣNi. Ni is the count or frequency for a group. Mi is the molecular weight of that group.
Yes. Relative frequencies work when they represent the distribution correctly. The calculator only needs positive grouped values with consistent weighting.
Enter molecular weight in g/mol. Chain count can be actual counts or proportional frequencies. Keep the same basis for every row.
Mw gives more influence to heavier chains. Mn treats every chain equally. Because of that, Mw is often equal to or higher than Mn.
DPn estimates the average number of repeat units per chain. It is calculated by dividing Mn by the repeat unit molecular weight.
PDI is Mw divided by Mn. It indicates how broad the molecular weight distribution is across the polymer sample.
Use CSV for spreadsheets and raw records. Use PDF for clean sharing, lab reports, batch reviews, or printed documentation.
Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.