Convert Millimeters of Water to Kilopascals

Formula

kPa = mmH₂O × 0.00980665

or kPa = mmH₂O ÷ 101.9716212978

Derivation from SI units:

• 1 mmH₂O = 1000 kg/m³ × 9.80665 m/s² × 0.001 m = 9.80665 Pa
• 1 kPa = 10³ Pa
• 1 mmH₂O = 9.80665 Pa ÷ 1000 Pa per kPa = 0.00980665 kPa

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

Worked examples

1. A reading of 25 mmH₂O converts to 0.24516625 kPa.
   25 mmH₂O × 0.00980665 = 0.24516625 kPa
2. A value of 250 mmH₂O is 2.4516625 kPa.
   250 mmH₂O × 0.00980665 = 2.4516625 kPa

Where it's used

Millimeters of Water are used for fan static pressure and duct design in Asia and Europe, while kilopascals appear in tyre pressure outside the United States (about 200–250 kPa for cars). 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.