Felt Weight to Thickness Converter

Industrial felt is classified by its density, thickness, and fiber content. The two main classification systems are the SAE (Society of Automotive Engineers) grades and the older F-number system. Understanding these grades helps you select the right felt for sealing, polishing, padding, vibration dampening, and filtration applications.

SAE Felt Grades: The SAE system classifies felt by density (weight per unit volume). Higher-density felt is firmer, more durable, and better for mechanical applications like washers, gaskets, and polishing. Lower-density felt is softer and better for padding, sound absorption, and craft projects.

• SAE F-1: Very soft, low density (approximately 0.21 g/cm3). Used for polishing, padding, and light-duty applications. Available in thicknesses from 1/16 inch (1.6 mm) to 1 inch (25.4 mm).
• SAE F-3: Soft to medium density (approximately 0.24 g/cm3). The most commonly available grade. Good for general-purpose sealing, cushioning, and craft work.
• SAE F-5: Medium density (approximately 0.28 g/cm3). Suitable for oil wicking, medium-duty gaskets, and mechanical spacing. Holds its shape better under moderate pressure.
• SAE F-7: Medium-firm density (approximately 0.32 g/cm3). Used for gaskets, washers, and applications requiring firmer support. Resists compression better than softer grades.
• SAE F-10: Firm density (approximately 0.37 g/cm3). Industrial-grade felt for high-compression gaskets, vibration dampening pads, and machine component spacing.
• SAE F-13: Very firm, high density (approximately 0.41 g/cm3). The hardest standard grade. Used for precision polishing wheels, heavy-duty gaskets, and mechanical components.
• SAE F-26: Premium high-density felt (approximately 0.50 g/cm3). Used for the most demanding industrial applications where dimensional stability under load is critical.

Wool vs synthetic felt: Traditional industrial felt is made from pressed wool fibers. Wool felt naturally resists flame, absorbs oil, and has excellent resilience (springs back after compression). Synthetic felt (polyester, acrylic, or rayon) is less expensive, more resistant to moisture and insects, and available in a wider range of colors. However, synthetic felt generally has lower heat resistance and poorer oil absorption than wool.

Pressed felt vs needle-punch felt: Pressed (or fulled) wool felt is made by applying heat, moisture, and pressure to wool fibers until they interlock permanently. This creates a dense, uniform material with no grain direction. Needle-punch felt is made by mechanically interlocking fibers with barbed needles. It is faster and cheaper to produce but less dense and uniform than pressed felt.

Thickness tolerances: Industrial felt thicknesses have relatively wide tolerances compared to machined materials. A sheet specified as 1/4 inch (6.35 mm) thick may actually measure anywhere from 5.5 mm to 7.0 mm depending on the grade and manufacturer. For critical-dimension applications, specify both the thickness and the tolerance required.

Turning a weight into a thickness

Craft felt is often sold by areal weight in grams per square metre rather than by thickness, and converting between the two is just the grade’s density. A sheet of thickness t millimetres made of felt with density ρ grams per cubic centimetre has an areal weight of:

grams per square metre = density (g/cm³) × thickness (mm) × 1,000

Rearranged, thickness (mm) = grams per square metre / (density × 1,000).

So 3 mm of SAE F-3 felt at 0.24 g/cm³ weighs 720 g/m². A 300 g/m² craft felt at the same density is 1.25 mm thick, near enough to the 1/16-inch stock most suppliers carry. This is the one piece of arithmetic that lets you compare a craft-shop listing quoted in GSM against an industrial spec sheet quoted in inches, and it is what the calculator above does in both directions.

Two cautions. The density figures are nominal for each grade, and real sheets vary by a few percent. And felt compresses: measure it under no load, because a caliper tightened down on F-1 will read noticeably thinner than the same sheet sitting loose.