Skip to main content
Calcimator

Melt Flow Index Interpretation Calculator

Interpret MFI test results to determine shear rate, apparent viscosity, molecular weight distribution breadth, and recommended processing method.

Inputs

Results

Wall shear rate (1/s)

19.43

Apparent viscosity (Pa·s)

996.1

Wall shear stress (Pa)19,358.67
Flow Rate Ratio (FRR)10
MWD breadth (1-4)1
Processability score (1-10)8
Process code3
Vol. flow rate (cm³/s)0.02
How to Use This Calculator
  1. Enter MFI at standard load (g/10 min), MFI at high load (g/10 min), and Melt density (g/cm³).
  2. Set Standard test load (kg) and Die diameter (mm).
  3. Review Wall shear rate (1/s) and Apparent viscosity (Pa·s).
  4. Use Wall shear stress (Pa) and Flow Rate Ratio (FRR) to inform your decision.

How the result changes with Die diameter (mm)

Die diameter (mm)Wall shear rate (1/s)Apparent viscosity (Pa·s)
0.95208.4342.12
2.0819.86967.88
3.434.437,157.19
4.551.922,162.14

What each input means

MFI at standard load (g/10 min)
Melt flow index measured at standard load (e.g., 2.16 kg for PE per ASTM D1238).
MFI at high load (g/10 min)
MFI measured at high load (typically 21.6 kg) for FRR calculation.
Melt density (g/cm³)
Polymer melt density at test temperature (PE ~0.76, PP ~0.73, PS ~0.96).
Standard test load (kg)
Dead weight load used for standard MFI measurement.
Die diameter (mm)
Extrusion plastometer die diameter. Standard is 2.095 mm.

What each result means

Wall shear rate (1/s)
Apparent shear rate at the die wall.
Apparent viscosity (Pa·s)
Ratio of wall shear stress to wall shear rate.
Wall shear stress (Pa)
Shear stress at the die wall from applied load.
Flow Rate Ratio (FRR)
Ratio of high-load MFI to standard MFI. Indicates MWD breadth.
MWD breadth (1-4)
1 = narrow, 2 = moderate, 3 = broad, 4 = very broad molecular weight distribution.
Processability score (1-10)
Higher = easier flow. Based on MFI range.
Process code
1 = extrusion, 2 = blow molding, 3 = injection molding, 4 = fiber/film.
Vol. flow rate (cm³/s)
Volumetric flow rate through the die.

How this is calculated

Worked example, using the default values

  1. Identify Input Parameters
    4 parameters
    MFI at standard load (g/10 min) = 10, MFI at high load (g/10 min) = 100, Melt density (g/cm³) = 0.95, Standard test load (kg) = 2.16 = 5 input(s) provided
  2. Calculate Wall shear rate
    Wall shear rate = (4 * volumeFlowMm3) / (π * pow(dieRadius, 3))
    19.43 = 19.43
  3. Calculate Apparent viscosity
    996.1 = 996.1
  4. Calculate Wall shear stress
    Wall shear stress = (dieRadius / 1000) * pressureDrop / (2 * (dieLength / 1000))
    19358.67 = 19358.67
  5. Calculate Flow Rate Ratio
    Flow Rate Ratio = mfiHighLoad / mfi
    10 = 10

Related Calculators

The questions that sit next to this one — chosen by subject, including calculators filed under a different category.

Plastics

Injection Molding Clamp Tonnage Calculator

Calculate required clamping force for injection molding from projected part area, cavity pressure, number of cavities, and runner system.

Injection Molding

Plastic Shrinkage Calculator

Calculate mold cavity dimensions from finished part size and material shrinkage rate to ensure correct part dimensions.

Gemology

Refractive Index Calculator

Interpret RI measurement and birefringence for gemstone identification against a reference database.

Plastics

Extrusion Die Swell Calculator

Calculate die swell ratio from material elasticity, L/D ratio, shear rate, and melt temperature. Determine required die dimensions to achieve target extrudate size.

Plastics

Thermoforming Draw Ratio Calculator

Calculate areal and linear draw ratios for thermoformed parts. Estimates wall thinning, minimum wall thickness, and forming feasibility.

More in Manufacturing, Industrial & Coatings.