What is the formula for corrosion rate in mpy?

The standard weight-loss formula is CR (mpy) = (534 × W) / (D × A × T), where W is weight loss in mg, D is metal density in g/cm³, A is exposed area in cm², and T is exposure time in hours. The constant 534 accounts for unit conversions to mils per year.

How do I convert mpy to mm/year?

Multiply mpy by 0.0254 to get mm/year. For example, 10 mpy equals 0.254 mm/year. This calculator shows both units simultaneously.

What density should I use for common metals?

Common values: carbon steel 7.87 g/cm³, stainless steel 304 7.93 g/cm³, aluminum 2.70 g/cm³, copper 8.96 g/cm³, brass (yellow) 8.47 g/cm³, titanium 4.51 g/cm³, zinc 7.13 g/cm³, nickel 8.90 g/cm³.

How do I measure the exposed area of a coupon?

For a rectangular coupon, calculate 2×(L×W + L×T + W×T) in cm² where L, W, T are length, width, and thickness. For cylindrical specimens use 2πr² + 2πrh. Subtract the area covered by the holding fixture if it was masked.

What corrosion rate is considered acceptable?

General guidelines: 50 mpy = unacceptable. Exact thresholds depend on the application, design life, and industry standard (NACE, ISO 9226).

Corrosion Rate Calculator

Name: Corrosion Rate Calculator
Availability: InStock
Author: Nham Vu

Calculate metal corrosion rate in mpy or mm/year from weight loss, density, area, and exposure time.

Coupon Test Inputs

Weight Loss (W) mg

Metal Density (D) g/cm³

Exposed Area (A) cm²

Exposure Time (T) hours

Results

Enter inputs and press Calculate.

Formula reference

CR (mpy) = (534 × W) / (D × A × T)
CR (mm/yr) = CR (mpy) × 0.0254
CR (µm/yr) = CR (mm/yr) × 1000

W = weight loss (mg)
D = metal density (g/cm³)
A = exposed area (cm²)
T = exposure time (hours)

Summary

Calculate metal corrosion rate in mpy or mm/year from weight loss, density, area, and exposure time.

How it works

Enter the weight loss of the metal coupon in milligrams (mg).
Enter the metal density in g/cm³ (e.g., 7.87 for carbon steel).
Enter the exposed surface area of the coupon in cm².
Enter the total exposure time in hours.
The calculator applies CR = (534 × W) / (D × A × T) for mpy and scales to mm/year automatically.

Use cases

Evaluate material selection for pipelines and pressure vessels.
Determine corrosion inhibitor effectiveness in laboratory coupon tests.
Monitor metal degradation rates in chemical processing plants.
Compare corrosion performance of alloys in saltwater or acidic environments.
Support corrosion engineering reports and fitness-for-service assessments.
Convert weight loss data from immersion tests to industry-standard rate units.

Frequently Asked Questions

Last updated: 2026-07-22 · Reviewed by Nham Vu