Millimetre per Year (mm/y)
The millimetre per year (mm/y, also mm/a) is the most common metric unit of corrosion rate: the average loss of metal thickness per year.
Symbol: mm/y
Quantity: corrosion rate (thickness loss per year)
SI relation: The millimetre per year is the reference unit for corrosion rate on this site. It is not a coherent SI unit (that would be metres per second), but it is the unit used in corrosion standards and data.
Derivation: Thickness loss in millimetres per year of exposure (the reference unit for corrosion rate)
Exact: yes, by definition
Typical uses
- Corrosion coupon and weight-loss tests
- Corrosion allowance in pipe and vessel design
- Material selection tables
Convert millimetres per year to other units
| Conversion | 1 mm/y equals | Reverse |
|---|---|---|
| millimetre per year to mil per year | 39.37007874 mpy | mil per year to millimetre per year |
| millimetre per year to micrometre per year | 1000 µm/y | micrometre per year to millimetre per year |
| millimetre per year to inch per year | 0.03937007874 ipy | inch per year to millimetre per year |
Open the Corrosion Rate Converter to convert any value between all units.
Sources
- Guide for the Use of the International System of Units (SI), NIST Special Publication 811, 2008 Edition, National Institute of Standards and Technology .
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). Millimetre per Year (mm/y). Retrieved October 25, 2026, from https://scientificconverters.com/units/millimeter-per-year/
IEEE
Scientific Converters, "Millimetre per Year (mm/y)," scientificconverters.com. Accessed: Oct. 25, 2026. [Online]. Available: https://scientificconverters.com/units/millimeter-per-year/