How Much Resin Per Yard of Fiberglass: Calculator Guide

Mark Cafero

28 February 2026

One of the most common questions we hear from DIY boat builders is: How much resin do I need per yard of fiberglass? Getting this calculation right is crucial.

Resin-to-Glass Ratios

Chopped Strand Mat (CSM): 2.5:1 to 3:1
Woven Cloth: 1:1 to 1.5:1
Woven Roving: 1:1 to 1.3:1
Biaxial Fabrics: 1:1 to 1.5:1

Basic Formula

Resin Required = Fabric Weight x Area x Resin Ratio

Fabric Type	Weight	Ratio	Resin/Sq Yd
0.75 oz CSM	0.75 oz	2.5:1	1.88 oz
1.5 oz CSM	1.5 oz	2.5:1	3.75 oz
6 oz Cloth	6 oz	1.25:1	7.5 oz
18 oz Roving	18 oz	1.2:1	21.6 oz

Fiberglass Types

Chopped Strand Mat

Chopped strand mat uses random fibers held by styrene-soluble binder. It requires the most resin because of air pockets in the random fiber orientation.

Woven Cloth

Fiberglass cloth has a tight weave that requires less resin to wet out. For guidance on selecting the right materials, consult our fiberglass buyer's guide.

Woven Roving

Woven roving is heavier and builds thickness quickly for structural applications. To understand the differences better, read our comparison on woven roving vs fiberglass cloth.

Biaxial Fabrics

Biaxial fabrics have oriented fibers for superior strength.

Factors Affecting Resin Usage

Laminating Technique

Hand layup: 10-15% more resin
Vacuum bagging: optimal ratios
Spray-up: up to 30% more resin

Temperature

Warmer temps thin resin (faster gel). Cold temps thicken it. Check your polyester resin data sheets.

Surface Porosity

Porous surfaces absorb resin. Add 10-20% for first layer on wood or foam.

Waste Factor

Small projects: Add 20-25%
Medium projects: Add 15-20%
Large projects: Add 10-15%

Example: Hull Repair

Repairing 2 ft x 3 ft (0.67 sq yd) with 1.5 oz CSM + 18 oz roving + 6 oz cloth:

CSM: 1.5 x 0.67 x 2.5 = 2.5 oz
Roving x2: 18 x 0.67 x 1.2 x 2 = 29 oz
Cloth: 6 x 0.67 x 1.25 = 5 oz
Total with 20% waste: 43.8 oz (2.7 lbs)

For specific repairs like transom work, see our guide on fiberglass boat transom repair, and learn about how many layers of fiberglass are needed for different repairs.