Convert CFM per Square Foot to L/(m²·s)

Formula

L/(m²·s) = ft³/(ft²·min) × 5.08

Derivation from SI units:

• 1 ft³/(ft²·min) = 0.3048³ m³ ÷ (0.3048² m² × 60 s) = 0.00508 m/s = 1 ft/min
• 1 L/(m²·s) = 10⁻³ m³ ÷ (1 m² × 1 s) = 10⁻³ m/s = 1 mm/s
• 1 ft³/(ft²·min) = 0.00508 m/s ÷ 0.001 m/s per L/(m²·s) = 5.08 L/(m²·s)

Both units are defined exactly, so the factor is exact. CFM per Square Foot definition: cubic foot per square foot per minute; Liter per Square Meter per Second definition: liter per square meter per second.

Worked examples

1. A fabric rated 20 ft³/(ft²·min) by ASTM D737 is 101.6 L/(m²·s).
   20 ft³/(ft²·min) × 5.08 = 101.6 L/(m²·s)
2. A nonwoven at 100 ft³/(ft²·min) is 508 L/(m²·s).
   100 ft³/(ft²·min) × 5.08 = 508 L/(m²·s)

Where it's used

US datasheets report air permeability in CFM/ft² (ASTM D737) and European ones in L/(m²·s) (ISO 9237). The unit factor is exactly 5.08, but compare only results measured at the same test pressure.

CFM per Square Foot to other face velocity & air permeability units

Frequently asked questions

Sources

• ASTM D737 Standard Test Method for Air Permeability of Textile Fabrics, ASTM International , inch-pound results in ft³/min/ft².
• Guide for the Use of the International System of Units (SI), NIST Special Publication 811, 2008 Edition, National Institute of Standards and Technology , Appendix B.8, "foot per minute".
• ISO 9237:1995 Textiles — Determination of the permeability of fabrics to air, International Organization for Standardization , air permeability expressed per unit area.
• The International System of Units (SI), 9th edition (SI Brochure), Bureau International des Poids et Mesures , Table 8 (litre).

Last reviewed: 2026-10-15. Factors are stored exactly and computed with 50-digit decimal arithmetic. See how we verify conversion factors.