Corrosion Rate Calculator
ASTM G1 gives corrosion rate = K × W / (A × T × D): a carbon steel coupon (7.86 g/cm³) losing 25 mg from 20 cm² in 720 h corrodes at 8.76 × 10⁴ × 0.025 ÷ (20 × 720 × 7.86) = 0.0193 mm/y, or 0.762 mpy.
0.0193490245971162 mm/y
Full answer, then cut to fewer decimals (not rounded):
- 0.0193490245971162 mm/y
- 0.019349024597116 mm/y
- 0.01934902459711 mm/y
- 0.0193490245971 mm/y
- 0.019349024597 mm/y
- 0.01934902459 mm/y
- 0.0193490245 mm/y
- 0.019349024 mm/y
- 0.01934902 mm/y
- 0.0193490 mm/y
- 0.019349 mm/y
- 0.01934 mm/y
- 0.0193 mm/y
- 0.019 mm/y
- 0.01 mm/y
- In ASTM G1 units: W = 0.025 g, A = 20 cm², T = 720 h, D = 7.86 g/cm³
- CR = 8.76 × 10⁴ × 0.025 ÷ (20 × 720 × 7.86) = 0.019349 mm/y
- = 19.349 µm/y
- = 0.761773 mpy
- = 0.000761773 ipy
- Uniform corrosion over 0.08219 years of exposure; pitting is not captured by mass loss.
Corrosion Rate Formula (ASTM G1)
CR = (K × W) / (A × T × D)
W mass loss (g), A exposed area (cm²), T exposure time (h), D density (g/cm³), K unit constant
| Corrosion rate unit | K |
|---|---|
| mils per year (mpy) | 3.45 × 10⁶ |
| inches per year (ipy) | 3.45 × 10³ |
| millimetres per year (mm/y) | 8.76 × 10⁴ |
| micrometres per year (µm/y) | 8.76 × 10⁷ |
The formula turns mass loss into an average thickness loss per year: W / (A × D) is the thickness removed, and dividing by T and scaling to a 365-day year (8760 h) gives the rate. The calculator works this out from your units exactly; the K values above are the rounded constants for the unit set given.
Worked Examples
- Carbon steel, 25 mg lost from 20 cm² in 720 h (30 days): CR = 0.0193 mm/y = 0.762 mpy.
- Stainless steel 304, 182.3 mg lost from 30 cm² in one week (168 h): CR = 0.399 mm/y = 15.7 mpy.
- Aluminium, 1.2 mg lost from 2 in² in 30 days: CR = 4190 µm/y = 165 mpy.
Reference
ASTM International. (2025). Standard practice for preparing, cleaning, and evaluating corrosion test specimens (ASTM G1-25). https://store.astm.org/g0001-25.html
The corrosion rate equation and constants are summarised in our own words; see the standard for specimen cleaning and evaluation procedures.
Frequently asked questions
What is the ASTM G1 corrosion rate formula?
Corrosion rate = (K × W) / (A × T × D), with W the mass loss in g, A the exposed area in cm², T the exposure time in hours and D the density in g/cm³. K sets the output unit: 8.76 × 10⁴ for mm/y or 3.45 × 10⁶ for mpy.
Where does K = 8.76 × 10⁴ come from?
W/(A·D) is a thickness in cm. Converting cm to mm (× 10) and per hour to per year (× 8760 h in a 365-day year) gives 87 600 = 8.76 × 10⁴.
Which area do I use for a coupon?
The total exposed area of all faces and edges, measured before exposure. Subtract areas covered by mounting or insulating washers.
What counts as a low corrosion rate?
As a common rule of thumb for carbon steel, below about 0.025 mm/y (1 mpy) is low, 0.025–0.12 mm/y moderate and above about 0.25 mm/y (10 mpy) severe. Acceptance limits depend on the corrosion allowance and design life.
Does mass loss detect pitting?
No. Mass loss gives an average uniform rate. Pitting or crevice attack can perforate a wall while the average rate looks low, so inspect coupons for pits as well.
What is the corrosion rate formula in mpy?
mpy = 3.45 × 10⁶ × W / (A × T × D) with W in g, A in cm², T in hours and D in g/cm³. With W in mg and A in in² the same formula is often written mpy = 534 W / (D A T).
How is corrosion rate calculated from wall thickness (API 510 / API 570)?
For inspected piping and vessels the corrosion rate is the thickness loss divided by the time between readings: CR = (t_previous − t_actual) / years, and the remaining life is (t_actual − t_required) / CR. This calculator covers the mass-loss (coupon) method instead.
Can I convert mpy to mm/y?
Yes. 1 mpy = 0.0254 mm/y exactly, and 1 mm/y = 39.37 mpy. Use the corrosion rate converter for any value.
Sources
- ASTM G1 Standard Practice for Preparing, Cleaning, and Evaluating Corrosion Test Specimens, ASTM International .
- 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). Corrosion Rate Calculator. Retrieved October 25, 2026, from https://scientificconverters.com/calculators/corrosion-rate/
IEEE
Scientific Converters, "Corrosion Rate Calculator," scientificconverters.com. Accessed: Oct. 25, 2026. [Online]. Available: https://scientificconverters.com/calculators/corrosion-rate/