Convert Gallons per Day per Square Foot to Inches per Hour

Formula

in/h = gpd/ft² × 0.06684027777778

or in/h = gpd/ft² ÷ 14.96103896104

Derivation from SI units:

• 1 gpd/ft² = 0.003785411784 m³ ÷ 86,400 s ÷ 0.09290304 m².
• 1 in/h = 0.0254/3600 m/s.
• 1 gpd/ft² = 4.715952932099 × 10⁻⁷ m/s ÷ 0.000007055555555556 m/s per in/h = 0.06684027777778 in/h

Both units are defined exactly, so the factor is exact. Gallon per Day per Square Foot definition: US gallon per day per square foot; Inch per Hour definition: inch per hour.

Worked examples

1. A reading of 100 gpd/ft² converts to 6.684027778 in/h.
   100 gpd/ft² × 0.06684027778 = 6.684027778 in/h
2. A value of 1000 gpd/ft² is 66.84027778 in/h.
   1000 gpd/ft² × 0.06684027778 = 66.84027778 in/h

Where it's used

Gallons per Day per Square Foot are used for older USGS and well-driller reports, while inches per hour appear in USDA soil survey permeability classes. Both measure hydraulic conductivity (coefficient of permeability k), so the conversion is a fixed factor.

Gallon per Day per Square Foot to other hydraulic conductivity 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, "gallon (U.S.)".
• 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".

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