How do you calculate fiber volume fraction?

Divide the fiber volume by the total cured laminate volume, then multiply by 100 to report as a percent. With 0.56 cu in of fiber in 1.00 cu in of laminate, Vf is 56%.

What is a good fiber volume fraction for carbon fiber composites?

Most structural aerospace prepreg laminates target 55-60% Vf, with autoclave-cured unidirectional tape reaching the high end. The 56% default sits right in the typical sweet spot for strength without resin starvation.

What happens if fiber volume fraction is too high?

Above roughly 65% the laminate becomes resin-starved: fibers are not fully wetted, interlaminar shear and toughness drop, and void content tends to rise. High Vf is not automatically better.

How is Vf measured on a real part?

Common methods are matrix burn-off (ASTM D2584), acid digestion (ASTM D3171), and image analysis of cross-sections. Each returns the fiber and total volumes you feed into this ratio.

Fiber volume fraction vs fiber weight fraction, what is the difference?

Weight fraction uses masses; volume fraction uses volumes. Because fiber and resin densities differ, the two values are not equal. Vf is what feeds stiffness and strength equations, so design work uses the volume basis.

Why use a conversion factor of 100?

The raw ratio of 0.56 is dimensionless. Multiplying by the 100 conversion factor expresses it as 56%, the form most specs and reports use. Set it to 1 if you want the bare fraction.

Composites, Fiberglass & Advanced Materials calculator

Fiber Volume Fraction Calculator

Fiber Volume Fraction (Vf) is the share of a cured composite occupied by reinforcing fiber rather than resin or voids, and it is the single strongest predictor of laminate stiffness and strength. Stress and design engineers, prepreg processors, and QA labs use Vf to confirm a part landed in its design window after cure. A laminate built too resin-rich is heavy and weak; too resin-starved and it loses interlaminar toughness. This calculator takes the fiber volume and the total cured volume and returns Vf as a clean percentage you can check against the allowable.

What this calculator does

Estimate fiber volume fraction from fiber volume and total composite volume.
checking fiber volume fraction against laminate specification
It divides the fiber volume by the total cured laminate volume and converts the ratio to a percentage, giving the fiber volume fraction.

Formula used

Fiber Volume Fraction = fiber volume in the laminate ÷ total cured laminate volume
Converted fiber volume fraction = fiber volume fraction × percentage reporting conversion

Inputs explained

Fiber volume in the cured laminate:
Total cured laminate volume:
Percent reporting conversion:

How to use the result

Use it after cure or burn-off/acid-digestion testing to verify a laminate hit its target Vf, or during design to back out the resin volume needed for a target fraction.
It is a pure volume ratio and does not separate void volume from resin; if your total volume includes porosity, the reported Vf is the as-measured value, not a void-free fiber fraction.

Current U.S. benchmarks

The producer price index for plastic resins and materials stands at 319.371 (BLS, May 2026), up 19.5% from a year earlier. Quotes priced off last quarter's material cost miss this move.
Steel mill PPI stands at 348.53 (BLS, May 2026), up 6.7% from a year earlier. New factory orders are up 2.3% year over year (Census).

Common questions

How do you calculate fiber volume fraction? Divide the fiber volume by the total cured laminate volume, then multiply by 100 to report as a percent. With 0.56 cu in of fiber in 1.00 cu in of laminate, Vf is 56%.
What is a good fiber volume fraction for carbon fiber composites? Most structural aerospace prepreg laminates target 55-60% Vf, with autoclave-cured unidirectional tape reaching the high end. The 56% default sits right in the typical sweet spot for strength without resin starvation.
What happens if fiber volume fraction is too high? Above roughly 65% the laminate becomes resin-starved: fibers are not fully wetted, interlaminar shear and toughness drop, and void content tends to rise. High Vf is not automatically better.
How is Vf measured on a real part? Common methods are matrix burn-off (ASTM D2584), acid digestion (ASTM D3171), and image analysis of cross-sections. Each returns the fiber and total volumes you feed into this ratio.
Fiber volume fraction vs fiber weight fraction, what is the difference? Weight fraction uses masses; volume fraction uses volumes. Because fiber and resin densities differ, the two values are not equal. Vf is what feeds stiffness and strength equations, so design work uses the volume basis.

Last reviewed 2026-05-12.