Inches per Hour to Millimetres per Hour (in/h to mm/h)
1 inch per hour (in/h) = 25.4 millimetres per hour (mm/h). 1 mm/h = 0.03937007874 in/h. Example: 15 in/h = 15 × 25.4 = 381 mm/h.
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1 in/h = 25.4 mm/h
Type in either box. Scientific notation works: 1.5e-3.
Converting a list? Use the bulk inch per hour to millimetre per hour converter to paste a column from Excel.
How to Convert Inch per Hour to Millimetre per Hour
- 1 in/h = 25.4 mm/h
- 1 mm/h = 0.03937007874 in/h
- Example: convert 15 in/h to mm/h: 15 in/h = 15 × 25.4 mm/h = 381 mm/h
Formula
mm/h = in/h × 25.4
Derivation from SI units:
- 1 in/h = 0.0254/3600 m/s.
- 1 mm/h = 0.001/3600 m/s.
- 1 in/h = 0.000007055555555556 m/s ÷ 2.777777777778 × 10⁻⁷ m/s per mm/h = 25.4 mm/h
Both units are defined exactly, so the factor is exact. Inch per Hour definition: inch per hour; Millimetre per Hour definition: millimetre per hour.
Worked examples
- A reading of 0.5 in/h converts to 12.7 mm/h.
0.5 in/h × 25.4 = 12.7 mm/h - A value of 3 in/h is 76.2 mm/h.
3 in/h × 25.4 = 76.2 mm/h
Inch per Hour to Millimetre per Hour conversion table
| Inches per Hour (in/h) | Millimetres per Hour (mm/h) |
|---|---|
| 0.05 in/h | 1.27 mm/h |
| 0.1 in/h | 2.54 mm/h |
| 0.2 in/h | 5.08 mm/h |
| 0.5 in/h | 12.7 mm/h |
| 1 in/h | 25.4 mm/h |
| 2 in/h | 50.8 mm/h |
| 3 in/h | 76.2 mm/h |
| 5 in/h | 127 mm/h |
| 10 in/h | 254 mm/h |
| 20 in/h | 508 mm/h |
Where it's used
Inches per Hour are used for USDA soil survey permeability classes, while millimetres per hour appear in sprinkler application rate versus infiltration. Both measure hydraulic conductivity (coefficient of permeability k), so the conversion is a fixed factor.
Inch per Hour to other hydraulic conductivity units
| Conversion | 1 in/h equals |
|---|---|
| inch per hour to millimetre per hour | 25.4 mm/h |
| inch per hour to metre per second | 0.000007055555556 m/s |
| inch per hour to centimetre per second | 0.0007055555556 cm/s |
| inch per hour to metre per day | 0.6096 m/day |
| inch per hour to centimetre per hour | 2.54 cm/h |
| inch per hour to foot per day | 2 ft/day |
| inch per hour to gpd/ft² | 14.96103896 gpd/ft² |
Frequently asked questions
How many millimetres per hour are in 1 inch per hour?
1 in/h = 25.4 mm/h.
How do I convert inches per hour to millimetres per hour?
Multiply the value in in/h by 25.4. For example, 15 in/h × 25.4 = 381 mm/h.
Is the in/h to mm/h conversion exact?
Yes. Both units are defined exactly, and 1 in/h is exactly 25.4 mm/h.
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".
- The International System of Units (SI), 9th edition (SI Brochure), Bureau International des Poids et Mesures , Table 4 (derived units) and Table 8 (non-SI units accepted for use with the SI).
Last reviewed: . Factors are stored exactly and computed with 50-digit decimal arithmetic. See how we verify conversion factors.
Cite this page
APA
Scientific Converters. (2026, October 15). Inches per Hour to Millimetres per Hour (in/h to mm/h). Retrieved October 29, 2026, from https://scientificconverters.com/hydraulic-conductivity/inches-per-hour-to-millimeters-per-hour/
IEEE
Scientific Converters, "Inches per Hour to Millimetres per Hour (in/h to mm/h)," scientificconverters.com. Accessed: Oct. 29, 2026. [Online]. Available: https://scientificconverters.com/hydraulic-conductivity/inches-per-hour-to-millimeters-per-hour/