What units is Melt Flow Index expressed in?

MFI is expressed in grams per 10 minutes (g/10 min). It represents the mass of polymer pushed through a standard 2.095 mm diameter die under a specified load at a controlled temperature over a 10-minute period.

What is the difference between MFI and MFR?

Melt Flow Index (MFI) and Melt Flow Rate (MFR) are used interchangeably and refer to the same measurement. The ISO 1133 standard uses "MFR" while older ASTM D1238 literature often uses "MFI". Both describe mass flow in g/10 min.

Can MFR alone identify processing suitability?

No. MFR is an empirical quality-control value measured at low shear. Material, preparation, temperature, load, method and specification all matter, and the result may not predict behavior in a production process.

Does the applied load affect the MFI result?

Yes. A higher load forces more polymer through the die, yielding a higher MFI number. Standard loads defined in ASTM D1238 include 2.16 kg, 5 kg, and 21.6 kg. Always report the test conditions (temperature and load) alongside the MFI value for a meaningful comparison.

How do I convert MFR to MVR?

MVR = MFR divided by melt density. Density must be measured or supplied at the test temperature; ordinary room-temperature density is not interchangeable.

Melt Flow Index Calculator

Calculate MFR (often called MFI) for up to five timed cuts, review repeatability, and optionally derive MVR from melt density at the test temperature.

Test Parameters

Enter up to five Procedure A-style timed cuts. One valid cut is enough.

Cut	Mass (g)	Time (s)
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5

Test temperature (°C)

Material / grade (optional)

Applied Load (kg)

Select the load specified by the material/test method; presets are conveniences, not recommendations.

Melt density at test temperature (g/cm³) (optional)

Do not use ordinary room-temperature density.

Interpret results safely

Only compare values produced with the same material preparation, temperature, load, method, and relevant standard conditions.
This calculator checks arithmetic; it does not certify ASTM D1238 or ISO 1133 compliance.
MFR is an empirical low-shear quality-control value, not a direct viscosity, molecular-weight, or processing-performance prediction.
Time/temperature- or moisture-sensitive materials can require a method specifically designed for that behavior.

Summary

Melt mass-flow rate (MFR), commonly called melt flow index (MFI), is the mass extruded in ten minutes under stated test conditions. The result is empirical: always report temperature, load, material preparation, and method. Melt volume-flow rate (MVR) can be related to MFR only with melt density measured at the test temperature.

How it works

Weigh the polymer sample extruded from the plastometer die.
Record the time interval over which the sample was collected.
Enter one or more extrudate cut masses and their collection times.
The calculator normalizes each cut to ten minutes: MFR = 600 × mass / time.
Review the mean, standard deviation, and coefficient of variation for the entered cuts.
Optionally enter melt density at the test temperature to calculate MVR = MFR / density.

Use cases

Quality control of incoming polymer resins before production.
Comparing flowability of different polymer grades for a new product.
Checking arithmetic while preparing ASTM D1238 or ISO 1133 laboratory reports.
Selecting the right polymer grade for injection molding vs. extrusion.
Monitoring batch-to-batch consistency in polymer manufacturing.
Academic labs teaching polymer processing fundamentals.
R&D evaluation of new polymer blends or additives.
Troubleshooting processing issues caused by viscosity variation.

Frequently Asked Questions

Last updated: 2026-09-30 · Reviewed by Nham Vu