Convert Inches of Water to Torr

Formula

Torr = inH₂O × 1.868320469775

Derivation from SI units:

• 1 inH₂O = 1000 kg/m³ × 9.80665 m/s² × 0.0254 m = 249.08891 Pa
• 1 Torr = 101325/760 Pa = 133.3223684 Pa (1/760 of a standard atmosphere)
• 1 inH₂O = 249.08891 Pa ÷ 133.3223684211 Pa per Torr = 1.868320469775 Torr

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

Worked examples

1. A reading of 0.3 inH₂O converts to 0.5604961409 Torr.
   0.3 inH₂O × 1.86832047 = 0.5604961409 Torr
2. A value of 3 inH₂O is 5.604961409 Torr.
   3 inH₂O × 1.86832047 = 5.604961409 Torr

Where it's used

Inches of Water are used for HVAC total external static pressure (residential ≈ 0.5 inH₂O), while torr appear in vacuum technology and vacuum gauges. 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)".
• 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, "torr (Torr)".

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