3 free online tools which calculate and convert weights and materials:

Resin Formula Calculator
Calculates the overall density and price of a resin system

Unit Converter
Converts between commonly used units for the linear weight of a roving, units for the areal weight of a fabric and between commonly used units for density

Volume-Weight Fraction and Density Calculator
Converts volume fractions to weight fractions and calculates the overall density of a composite.