Fiberglass Weight & Resin Calculator
Calculate laminate weight and how much resin you need from area, number of layers and cloth weight — with presets for mat, woven roving and biaxial.
How to estimate fiberglass weight and resin
The weight of a laminate is the glass reinforcement plus the resin that wets it out. Glass weight comes straight from the cloth's areal weight (g/m²); resin is then a multiple of the glass weight set by the resin-to-glass ratio, which depends on the cloth type and how you lay it up.
The formula
Glass (kg) = Area × Layers × g/m² ÷ 1000
Resin (kg) = Glass × resin:glass ratio
Resin (L) = Resin (kg) ÷ 1.1
Resin density is roughly 1.1 kg per litre for polyester, vinylester and epoxy.
Typical resin-to-glass ratios
| Reinforcement | Resin : glass |
|---|---|
| Chopped strand mat (CSM) | ~2.5 : 1 |
| Plain / light cloth | ~1.5 : 1 |
| Biaxial / stitched | ~1.3 : 1 |
| Woven roving | ~1 : 1 |
Mat soaks up the most resin; tightly woven and stitched fabrics need the least. Vacuum bagging and infusion push ratios well below 1:1.
Related construction tools
To dial in the laminate ratio for strength, use the fiberglass ratio calculator. For structural parts, check the transom thickness and structural load calculators.
Note: real resin uptake varies with temperature, layup method and operator. Always mix resin in manufacturer-specified batches and order a margin for waste.
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See what's insideFrequently Asked Questions
How much resin do I need per square metre of fiberglass?
It depends on the cloth and ratio. Chopped strand mat soaks up about 2.5 times its own weight in resin, woven roving roughly 1:1. For 450 g/m² mat that is about 1.1 kg of resin per m² per layer; for 600 g/m² woven roving about 0.6 kg per m² per layer. Add 5–10% for waste.
How do you calculate laminate weight?
Glass weight = area × number of layers × cloth weight (g/m²) ÷ 1000. Resin weight = glass weight × the resin-to-glass ratio. Add them together for total laminate weight, then divide by area for kg per m². This calculator does all of that, including resin volume in litres.
What is a good resin-to-glass ratio?
Lower is stronger and lighter. Hand-laid chopped strand mat runs about 2.5:1, plain cloth about 1.5:1, biaxial around 1.3:1 and woven roving near 1:1. Vacuum bagging and resin infusion can drop below 1:1, giving a higher glass content and stiffer, lighter parts.