Unit Conversion Guides
Explanations behind the numbers: what each unit means, where conversions go wrong, and how to check a result.
- Air Permeability Units Explained Air permeability is a flow divided by an area, so every air permeability unit is a velocity: 1 L/(m²·s) = 1 mm/s, 1 cm³/(s·cm²) = 1 cm/s = 10 mm/s, and 1 cfm/ft² = 1 ft/min = 5.08 mm/s exactly.
- Pa vs inH₂O for Filter Pressure Drop One conventional inch of water is exactly 249.08891 Pa, so filter pressure drops convert at about 250 Pa per inH₂O: 125 Pa ≈ 0.50 inH₂O and 1.0 inH₂O ≈ 249 Pa.
- Standard Test Areas in Textile and Membrane Testing ISO 9237 uses a 20 cm² test area (with 5, 50 and 100 cm² alternatives) and ASTM D737 uses 38.3 cm² (about 5.94 in²); permeability is the measured flow divided by that area.
- sccm vs SLPM vs Actual Flow sccm and SLPM are standard flows referenced to fixed conditions (often 0 °C and 101.325 kPa), so they measure the amount of gas; actual flow in cm³/min or L/min is the volume at line conditions: Q_actual = Q_std × (T/T_ref) × (P_ref/P).
- Celsius, Fahrenheit and Kelvin: How the Scales Relate °F = °C × 1.8 + 32 and K = °C + 273.15 exactly; a temperature difference converts without the offset, so a 10 °C rise is an 18 °F rise.
- Dynamic vs Kinematic Viscosity (cP vs cSt) Kinematic viscosity equals dynamic viscosity divided by density, ν = μ/ρ; in practical units cSt = cP ÷ (density in g/cm³), so an oil of 90 cP and 0.9 g/cm³ is 100 cSt.