Corrosion Rate Calculator (Mils per Year)
Calculate metal corrosion rate in mils per year (MPY) and mm/year from weight loss data.
Includes corrosion rating classification.
Corrosion Rate
Corrosion Rate Formula (ASTM G31) MPY = (534 × W) / (D × A × T)
Where W = weight loss (mg), D = material density (g/cm³), A = exposed area (cm²), T = exposure time (hours).
The constant 534 converts units to mils per year (1 mil = 0.001 inch).
Conversion to mm/year mmpy = MPY × 0.0254
Corrosion Rate Rating < 1 MPY: Excellent. 1–5 MPY: Good. 5–20 MPY: Fair. 20–50 MPY: Poor. > 50 MPY: Unacceptable.