Convert Centimeters of Water to N/mm²

Formula

N/mm² = cmH₂O × 0.0000980665

or N/mm² = cmH₂O ÷ 10197.16212978

Derivation from SI units:

• 1 cmH₂O = 1000 kg/m³ × 9.80665 m/s² × 0.01 m = 98.0665 Pa
• 1 N/mm² = 1 N ÷ 10⁻⁶ m² = 10⁶ Pa = 1 MPa
• 1 cmH₂O = 98.0665 Pa ÷ 1000000 Pa per N/mm² = 0.0000980665 N/mm²

Both units are defined exactly, so the factor is exact. Centimeter of Water definition: centimeter of water; Newton per Square Millimetre definition: newton per square millimetre.

Worked examples

1. A reading of 6 cmH₂O converts to 0.000588399 N/mm².
   6 cmH₂O × 0.0000980665 = 0.000588399 N/mm²
2. A value of 30 cmH₂O is 0.002941995 N/mm².
   30 cmH₂O × 0.0000980665 = 0.002941995 N/mm²

Where it's used

Centimeters of Water are used for mechanical ventilation (PEEP 5–10 cmH₂O, plateau pressure under 30 cmH₂O), while newtons per square millimetre appear in steel yield and tensile strength (S355: 355 N/mm²). Both measure pressure, stress and differential pressure (force per unit area), so the conversion is a fixed factor.

Centimeter of Water to other pressure units

Frequently asked questions

Sources

• 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, "centimeter of water, conventional (cmH2O)".
• The International System of Units (SI), 9th edition (SI Brochure), Bureau International des Poids et Mesures , Table 4, coherent derived units with special names.

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