Convert Mils per Year to Millimetres per Year (mpy to mm/y)
1 mil per year (mpy) = 0.0254 millimetres per year (mm/y). 1 mm/y = 39.37007874 mpy. Example: 5 mpy = 5 × 0.0254 = 0.127 mm/y.
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1 mpy = 0.0254 mm/y
Type in either box. Scientific notation works: 1.5e-3.
Converting a list? Use the bulk mil per year to millimetre per year converter to paste a column from Excel.
How to Convert Mil per Year to Millimetre per Year
- 1 mpy = 0.0254 mm/y
- 1 mm/y = 39.37007874 mpy
- Example: convert 5 mpy to mm/y: 5 mpy = 5 × 0.0254 mm/y = 0.127 mm/y
Formula
mm/y = mpy × 0.0254
or mm/y = mpy ÷ 39.37007874016
Derivation from SI units:
- 1 mpy = 0.001 in per year = 0.0254 mm/y (exact)
- Thickness loss in millimetres per year of exposure (the reference unit for corrosion rate)
Both units are defined exactly, so the factor is exact. Mil per Year definition: mil per year; Millimetre per Year definition: millimetre per year.
Worked examples
- A corrosion rate of 5 mpy is 0.127 mm/y.
5 mpy × 0.0254 = 0.127 mm/y - A 1 mpy rate, often taken as the limit for good resistance, is 0.0254 mm/y.
1 mpy × 0.0254 = 0.0254 mm/y
Mil per Year to Millimetre per Year conversion table
| Mils per Year (mpy) | Millimetres per Year (mm/y) |
|---|---|
| 0.1 mpy | 0.00254 mm/y |
| 0.5 mpy | 0.0127 mm/y |
| 1 mpy | 0.0254 mm/y |
| 2 mpy | 0.0508 mm/y |
| 3 mpy | 0.0762 mm/y |
| 5 mpy | 0.127 mm/y |
| 10 mpy | 0.254 mm/y |
| 20 mpy | 0.508 mm/y |
| 50 mpy | 1.27 mm/y |
| 100 mpy | 2.54 mm/y |
Where it's used
Corrosion rates in mils per year from US coupon tests and monitoring reports are converted to mm/y for ISO and metric design. Multiply by 0.0254.
Mil per Year to other corrosion rate units
| Conversion | 1 mpy equals |
|---|---|
| mil per year to millimetre per year | 0.0254 mm/y |
| mil per year to micrometre per year | 25.4 µm/y |
| mil per year to inch per year | 0.001 ipy |
Frequently asked questions
How do I convert mpy to mm/y?
Multiply by 0.0254 (exact): 10 mpy = 0.254 mm/y.
Is mpy millimetres per year?
No. The "mil" is a thousandth of an inch, so 1 mpy = 0.0254 mm/y, about 39 times smaller than 1 mm/y.
How many millimetres per year are in 1 mil per year?
1 mpy = 0.0254 mm/y.
How do I convert mils per year to millimetres per year?
Multiply the value in mpy by 0.0254, or divide it by 39.37007874. For example, 5 mpy × 0.0254 = 0.127 mm/y.
Is the mpy to mm/y conversion exact?
Yes. Both units are defined exactly, and 1 mpy is exactly 0.0254 mm/y.
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, "mil".
- 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). Convert Mils per Year to Millimetres per Year (mpy to mm/y). Retrieved October 25, 2026, from https://scientificconverters.com/corrosion-rate/mils-per-year-to-millimeters-per-year/
IEEE
Scientific Converters, "Convert Mils per Year to Millimetres per Year (mpy to mm/y)," scientificconverters.com. Accessed: Oct. 25, 2026. [Online]. Available: https://scientificconverters.com/corrosion-rate/mils-per-year-to-millimeters-per-year/