Convert Inches of Water to Megapascals

Formula

MPa = inH₂O × 0.00024908891

or MPa = inH₂O ÷ 4014.630759756

Derivation from SI units:

• 1 inH₂O = 1000 kg/m³ × 9.80665 m/s² × 0.0254 m = 249.08891 Pa
• 1 MPa = 10⁶ Pa = 1 N/mm²
• 1 inH₂O = 249.08891 Pa ÷ 1000000 Pa per MPa = 0.00024908891 MPa

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

Worked examples

1. A reading of 0.3 inH₂O converts to 0.000074726673 MPa.
   0.3 inH₂O × 0.00024908891 = 0.000074726673 MPa
2. A value of 3 inH₂O is 0.00074726673 MPa.
   3 inH₂O × 0.00024908891 = 0.00074726673 MPa

Where it's used

Inches of Water are used for HVAC total external static pressure (residential ≈ 0.5 inH₂O), 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.

Inch 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, "inch of water, conventional (inH2O)".
• 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.