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Laminate Thickness and Weight from Ply Schedule Worksheet

A ply schedule is the contract between design and the shop floor: it states how many plies, in which orientation and at which areal weight. This worksheet turns that schedule into cured thickness, prepreg quantity and part mass so engineering, estimating and planning all work from the same numbers.

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Group thickness (mm)	Fiber weight (g/m2)	Prepreg weight (g/m2)	Prepreg mass in part (kg)
0.21	193	332.76	0.2063
0.28	300	461.54	0.2769
0.56	600	923.08	0.5354
0.84	900	1,384.62	0.1108
0.28	300	461.54	0.2677
0.21	193	332.76	0.1997

Total plies

Sum of group thickness (mm, at full coverage)

2.38

Fiber weight stack (g/m2)

2,486

Total prepreg mass in part (kg)

1.5967

Equivalent Vf, carbon at 1.78 g/cm3

58.7%

Fiber areal weight divided by fiber density times thickness. Valid only if the schedule is all carbon and fully covers the same area.

Average cured ply thickness

0.1488

mm per ply.

Group thickness is plies times cured ply thickness. Prepreg weight is fiber areal weight divided by (1 - resin content). Part mass uses the coverage area of each group, so doublers add mass only where they sit. The equivalent Vf summary assumes carbon fiber at 1.78 g/cm3 and full coverage, so use it as a sanity check against the supplier cured ply thickness. Resin bleed in an autoclave cure removes mass, so actual cured part weight is lower than the prepreg mass shown. Add trim and scrap on top for ordering.

Roll up ply books from the ERP

Optional: see how ply schedules in your BOM and routing can feed thickness, kit weight and cost automatically.

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How to use the worksheet

Add one row per ply group, meaning a run of plies sharing the same material, areal weight and coverage area. Enter the number of plies, fiber areal weight (FAW) in g/m2, resin content in percent by weight, the cured ply thickness from the datasheet, and the area the group covers in square meters. The sheet calculates thickness, fiber weight, prepreg weight and the kilograms of prepreg that group puts into the part. Totals sum the stack. Export to Excel to attach it to a traveler, routing or quote.

Use partial-coverage groups for doublers, pad-ups and ply drops.
Take cured ply thickness from the material datasheet or from measured coupons.
Keep fiber areal weight and resin content on the same basis as the datasheet.

Formulas and assumptions

Prepreg areal weight equals FAW divided by (1 - RC), where RC is the resin content as a fraction of total prepreg weight. Cured thickness is plies multiplied by the cured ply thickness, which already reflects the nominal resin bleed of the qualified cure cycle. Fiber volume fraction follows from FAW divided by fiber density and ply thickness. For a 150 g/m2 carbon UD ply at 0.14 mm the equivalent Vf is about 60%, consistent with autoclave prepreg. Part mass here is uncured prepreg mass, so cured mass is lower by the resin that bleeds into breather plies.

Reading the result

The default schedule has 16 plies and about 2.5 mm of nominal thickness over the main panel, with a local doubler of six plies raising the thickness to roughly 3.3 mm. Check the average ply thickness against the supplier value: a measured part that is thicker than predicted usually means under-bleed, bridging or too much resin, while a thinner part points to over-bleed or a low-resin lot. Use the prepreg mass total to size the kit, then add ply nesting waste before you order material.

Common mistakes

Mixing resin content definitions is the classic error: some suppliers quote resin content on prepreg, others on cured laminate, and the two differ after bleed. Another is forgetting that woven fabrics have a different cured ply thickness than UD tape at the same weight. Do not treat the summed doubler thickness as the thickness of the whole panel, because the sum assumes full coverage. For thick or tapered parts, also check that ply drop rules and symmetry and balance rules from your design allowables are met.

Frequently Asked Questions

How do I calculate cured laminate thickness from the ply schedule?

Multiply the number of plies by the cured ply thickness for each material and sum the groups. Use the supplier's nominal cured ply thickness for the qualified cure cycle, or a measured value from your own coupons, since it depends on resin content and bleed.

What is the difference between fiber areal weight and prepreg areal weight?

Fiber areal weight is the dry fiber mass per square meter. Prepreg areal weight adds the resin: it equals FAW divided by one minus the resin content fraction. A 150 g/m2 FAW at 35% resin content is about 231 g/m2 of prepreg.

Why is my cured part lighter than the worksheet predicts?

The worksheet reports uncured prepreg mass. During cure some resin bleeds into breather and bleeder materials, typically a few percent of resin weight, so the cured part weighs less. Weigh a few parts to build a shop-specific bleed factor.

Can I use this for glass or aramid laminates?

Yes for thickness and mass, which do not depend on fiber type. The equivalent Vf summary assumes carbon at 1.78 g/cm3, so ignore that line or recompute it with your fiber density for glass (about 2.55) or aramid (about 1.44).

If your ply books and kits live as BOMs and routings in the ERP, Netray can generate this thickness and weight roll-up directly from the structure, on-premises if required.

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