FIBERGLASS RESIN CALCULATOR

This calculator provides a reliable estimation based on standard coverage rates and typical resin-to-fabric ratios. Actual usage may vary depending on surface condition, application method, and how many laminate layers you apply, so it’s a good idea to allow for a little extra material.

The right fabric depends on what you’re trying to do—whether it’s a smooth finish, general repair, or structural strength. Each fabric type in the calculator is designed for a specific purpose:

Chopped Strand Mat (CSM): Best for building thickness and conforming to curves. CSM wets out easily and is commonly used in repairs and layering, especially with polyester resin. It uses more resin than woven fabrics.

Lightweight Cloth (up to 4 oz): Ideal for surface work, sheathing wood, and finishing. These fabrics lay down smoothly, turn transparent when wet out, and require less resin. Tape is great for seams, edges, and reinforcing joints.

Medium Cloth (4-10 oz): A good all-around option for reinforcement and repairs. It offers a balance of strength and conformability while still finishing relatively smooth.

Biaxial Cloth (12-18 oz, 1708): Designed for strength. Biaxial fabrics use stitched fibers instead of a tight weave, allowing them to handle higher loads. 1708 includes a mat backing, making it a strong choice for structural repairs and rebuilds—but it requires more resin.

Woven Roving (18 oz, 24 oz): Heavy, open-weave fabric used for building strength and thickness in larger laminations. It’s strong but doesn’t conform as easily and uses significantly more resin. Often paired with mat in layered builds.

Dynel Fabric: A common fiberglass alternative, this fabric is used when durability and abrasion resistance matter most. Dynel is great for high-wear areas and creates a tough, textured surface, but it absorbs more resin than fiberglass cloth.

Both epoxy resins and polyester resins can be used with fiberglass, but they behave a bit differently. Epoxy typically wets out fabric more efficiently and bonds well to a wider range of surfaces. Polyester is commonly used in fiberglass builds and repairs. The calculator works for both, but actual usage may vary slightly depending on the system you choose.

Some fiberglass materials, like chopped strand mat (CSM), are designed to work with polyester or vinyl ester resins. Standard mat contains a binder that helps it hold together, and that binder does not break down properly with epoxy. 

Once you've determine what resin type and reinforcement fabric to work with, build your own resin and fiberglass kit with our interactive bundle tool.

Different fabrics absorb resin differently. Lightweight woven cloth has a tight weave and uses less resin, while heavier or more open fabrics like woven roving and chopped strand mat have more space between fibers and require more resin to fully saturate. That’s why the calculator adjusts based on fabric type.

A little extra goes a long way. Resin gets lost during mixing, application, and overlap areas. Irregular shapes and edges also increase usage. Running out mid-layup can lead to poor bonding between layers, so adding 10–15% helps keep your project on track.

Too little resin can leave dry spots, which weakens the laminate. Too much resin doesn’t add strength—it just adds weight and can lead to a less efficient layup. The goal is to fully wet out the fabric without leaving excess resin on the surface.

Yes. Porous surfaces like bare wood or foam can absorb resin before the fabric is fully saturated, which increases total usage. Sealed or previously coated surfaces typically require less resin.

Yes—it can make a big difference in how much resin your project actually uses.

Hand layup (brush or roller): This is the most common method and typically uses more resin. When applying by hand, it’s easy to leave excess resin in the laminate or on the surface. Some resin is also lost in rollers, brushes, and mixing containers. Because you’re relying on manual pressure to wet out the fabric, laminates tend to be slightly more resin-rich.

Vacuum bagging (more controlled): Vacuum bagging applies even pressure across the laminate and actively removes excess resin and trapped air. This results in a tighter, more efficient laminate with a higher resin-to-fabric ratio. Since less excess remains in the finished part, total resin usage is typically lower.

The number of layers depends on your project, the level of strength required, and the type of fabric you’re using. There’s no one-size-fits-all answer, but there are a few reliable ways to determine what you need. If you’re repairing or rebuilding something like a boat hull, transom, or deck, the best starting point is matching the original construction. Use the same number of layers, and similar fabric types, whenever possible. Taper and feather the surrounding area and rebuild to the original thickness to maintain strength and a smooth transition between old and new material.

Every project is different. If you’re unsure, reach out to the TotalBoat Total Support Team. They can help you choose the right fabric, resin, and application method to get the job done.