Convert Millimeters of Water to Megapascals (mmH2O to MPa)

Formula

MPa = mmH₂O × 0.00000980665

or MPa = mmH₂O ÷ 101971.6212978

Derivation from SI units:

• 1 mmH₂O = 1000 kg/m³ × 9.80665 m/s² × 0.001 m = 9.80665 Pa
• 1 MPa = 10⁶ Pa = 1 N/mm²
• 1 mmH₂O = 9.80665 Pa ÷ 1000000 Pa per MPa = 0.00000980665 MPa

Both units are defined exactly, so the factor is exact. Millimeter of Water definition: millimeter of water; Megapascal definition: megapascal.

Worked examples

1. A reading of 25 mmH₂O converts to 0.00024516625 MPa.
   25 mmH₂O × 0.00000980665 = 0.00024516625 MPa
2. A value of 250 mmH₂O is 0.0024516625 MPa.
   250 mmH₂O × 0.00000980665 = 0.0024516625 MPa

Where it's used

Millimeters of Water are used for fan static pressure and duct design in Asia and Europe, while megapascals appear in concrete compressive strength (typically 20–50 MPa). Both measure pressure, stress and differential pressure (force per unit area), so the conversion is a fixed factor.

Millimeter 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, "millimeter of water, conventional (mmH2O)".
• The International System of Units (SI), 9th edition (SI Brochure), Bureau International des Poids et Mesures , Table 7, SI prefixes.

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