How do you calculate melt flow index?

Weigh an extrudate cut collected over a measured time and scale it to 10 minutes: MFR (g/10 min) = 600 × mass (g) ÷ time (s). A 2.45 g cut collected in 60 s gives 600 × 2.45 ÷ 60 = 24.5 g/10 min. Average several cuts from the same charge.

What units is melt flow index expressed in?

Grams per 10 minutes (g/10 min). It is the mass extruded through a die of 2.095 mm bore and 8.000 mm length under a specified load at a controlled temperature. MVR is the volume version, in cm³/10 min.

What is the difference between MFI, MFR and melt index?

They describe the same measurement. ISO 1133 calls it melt mass-flow rate (MFR); older ASTM D1238 literature and industry use melt flow index (MFI); "melt index" usually means polyethylene at 190 °C / 2.16 kg.

How do I convert MFR to MVR?

MVR (cm³/10 min) = MFR (g/10 min) ÷ melt density (g/cm³) at the test temperature. Melt density is much lower than solid density; ASTM D1238 gives 0.7636 g/cm³ for polyethylene at 190 °C and 0.7386 g/cm³ for polypropylene at 230 °C.

How is MFR calculated from piston travel (Procedure B)?

The plastometer times how long the piston takes to travel a set distance. MVR = A × 600 × l ÷ t, where A = 0.711 cm² (the mean of the piston and barrel cross-sections), l is travel in cm and t is time in s, so MVR = 427 × l ÷ t. Multiply by melt density to get MFR.

What test conditions are used for common polymers?

Typical conditions are PE 190 °C / 2.16 kg, PP 230 °C / 2.16 kg, PS 200 °C / 5 kg, ABS 220 °C / 10 kg, PC 300 °C / 1.2 kg, PMMA 230 °C / 3.8 kg and POM 190 °C / 2.16 kg. The material specification always takes precedence.

What is the flow rate ratio?

FRR is the MFR at a high load divided by the MFR at a low load at the same temperature, for example MFR(190 °C / 21.6 kg) ÷ MFR(190 °C / 2.16 kg) for PE. A higher FRR indicates a broader molecular-weight distribution and more shear thinning.

Can MFR alone identify processing suitability?

No. MFR is measured at low shear rate and is an empirical quality-control value. Compare only results from the same temperature, load, preparation and method, and use rheology for processing decisions.

Melt Flow Index Calculator

MFR (g/10 min) = 600 × cut mass (g) ÷ cut time (s). From piston travel, MVR (cm³/10 min) = 427 × travel (cm) ÷ time (s), and MFR = MVR × melt density. Pick a polymer to load its standard temperature and load.

Test Parameters

Polymer (loads standard conditions)

Enter up to five timed cuts. One valid cut is enough.

Cut	Mass (g)	Time (s)
1
2
3
4
5

Test temperature (°C)

Material / grade (optional)

Applied load (kg)

Use the load required by the material specification.

Melt density at test temperature (g/cm³) (optional in A, needed for MFR in B)

Do not use room-temperature density: solid PE and PP are about 20–25% denser than their melts.

Flow rate ratio (FRR)

Same temperature, two loads. For PE: MFR at 21.6 kg (HLMI) ÷ MFR at 2.16 kg (MI).

MFR at high load

MFR at low load

Enter both values.

Interpret results safely

Only compare values produced with the same material preparation, temperature, load and method.
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 prediction.
Moisture- or time-temperature-sensitive materials (PET, PBT, PA, PLA) need ISO 1133-2 conditioning.

Standard melt flow test conditions by polymer

Usual conditions from ISO 1133 / ASTM D1238 material designations. The resin's own specification takes precedence.

Polymer	Temperature	Load	Notes
Polyethylene (PE: HDPE, LDPE, LLDPE)	190 °C	2.16 kg	Melt density 0.7636 g/cm³ (ASTM D1238). Also 5 kg and 21.6 kg (HLMI) for low-MFR grades
Polypropylene (PP)	230 °C	2.16 kg	Melt density 0.7386 g/cm³ (ASTM D1238).
Polystyrene (PS, HIPS)	200 °C	5 kg
ABS	220 °C	10 kg
SAN	220 °C	10 kg
Polycarbonate (PC)	300 °C	1.2 kg	Dry the pellets before testing
PMMA (acrylic)	230 °C	3.8 kg
Acetal (POM)	190 °C	2.16 kg
PBT	250 °C	2.16 kg	Moisture-sensitive: dry first (see ISO 1133-2)
EVA	190 °C	2.16 kg
PLA	210 °C	2.16 kg	Moisture-sensitive: dry first (see ISO 1133-2)

Nominal loads and piston force

Nominal load = piston + weight. Force = mass × 9.80665 m/s²; pressure on the melt uses the 9.474 mm piston head.

Load	Force	Pressure
0.325 kg	3.19 N	0.45 bar
1.2 kg	11.77 N	1.67 bar
2.16 kg	21.18 N	3.00 bar
3.8 kg	37.27 N	5.29 bar
5 kg	49.03 N	6.96 bar
10 kg	98.07 N	13.91 bar
12.5 kg	122.58 N	17.39 bar
21.6 kg	211.82 N	30.05 bar

Formulas and worked examples

Procedure A (mass): MFR (g/10 min) = 600 × m ÷ t, with m the cut mass in g and t the cut time in s.
Procedure B (volume): MVR (cm³/10 min) = A × 600 × l ÷ t = 427 × l ÷ t, with A = 0.711 cm², l the piston travel in cm and t in s.
Conversion: MFR = MVR × ρ_melt; MVR = MFR ÷ ρ_melt.
Flow rate ratio: FRR = MFR(high load) ÷ MFR(low load), same temperature.

Example A: a PP cut of 2.45 g collected in 60 s at 230 °C / 2.16 kg gives 600 × 2.45 ÷ 60 = 24.5 g/10 min. With melt density 0.7386 g/cm³, MVR = 24.5 ÷ 0.7386 = 33.17 cm³/10 min.

Example B: a PE piston travels 25.4 mm (2.54 cm) in 120 s at 190 °C / 2.16 kg: MVR = 0.711 × 600 × 2.54 ÷ 120 = 9.03 cm³/10 min, and MFR = 9.03 × 0.7636 = 6.90 g/10 min.

Summary

Melt mass-flow rate (MFR), commonly called melt flow index (MFI) or melt index, is the mass of polymer extruded through a 2.095 mm × 8 mm die in ten minutes at a stated temperature and load. Procedure A weighs timed cuts; Procedure B times piston travel and gives the melt volume-flow rate (MVR), which converts to MFR with melt density at the test temperature. The value is empirical: always report temperature and load.

How it works

Pick the polymer to load its usual test temperature and load, or type your own.
Procedure A: enter the mass and collection time of one to five extrudate cuts. MFR = 600 × mass ÷ time for each cut, then the mean, SD and CV.
Procedure B: enter the piston travel and the time it took. MVR = 0.711 cm² × 600 s × travel ÷ time = 427 × travel (cm) ÷ time (s).
Enter melt density at the test temperature to convert MFR to MVR (MVR = MFR ÷ ρ) or MVR to MFR (MFR = MVR × ρ).
Optionally enter MFR at a high and a low load to get the flow rate ratio (for PE: MFR 21.6 kg ÷ MFR 2.16 kg).

Use cases

Quality control of incoming polymer resin lots against a data-sheet MFR.
Checking arithmetic for ASTM D1238 or ISO 1133 Procedure A and B laboratory reports.
Converting MVR from an automated plastometer to MFR for a specification written in g/10 min.
Comparing molecular-weight distribution breadth of PE grades with the flow rate ratio (HLMI/MI).
Selecting grades for injection molding (higher MFR) versus extrusion and blow molding (lower MFR).
Monitoring batch-to-batch consistency and degradation after regrind or drying.

Frequently Asked Questions

Last updated: 2026-10-09 · Reviewed by Nham Vu