In the modern world, international commerce has become commonplace, if not vital, to many companies’ business plans. However, America is one of the few countries that still uses the Imperial Measurement System, a remnant of our country’s British heritage, while most of the world has converted to the metric system. So how do we communicate the correct information to our international counterparts regarding ASTM A123 coating weight and thickness requirements? Luckily, with some basic arithmetic, this is easily solved. And to make it even easier, the AGA has put together some resources to help make your conversions simple and accurate.

First, you can use a calculator and the constants listed in ASTM A123 Table 2.

• mils = µm x 0.03937
• oz/ft² = µm x 0.02316
• g/m² = µm x 7.067

It’s important to remember that microns (µm) and coating grade have the same value. For example, if a coating grade of 75 is required, this means 75 microns (µm). We can multiply 75 by 0.03937 to get required mils (2.95), multiply 75 by 0.02316 to get ounces per square feet [oz/ft²] (1.74), or multiply 75 by 7.067 to get grams per square meter [g/m²] (530.03):

• 75 (grade or µm) x 0.03937 = 2.95 mils
• 75 (grade or µm) x 0.02316 = 1.74 oz/ft²
• 75 (grade or µm) x 7.067 = 530.03 g/m²

In a situation where the coating grade or µm is unknown, we can add the extra step of converting the known measurement to grade or µm first, and then making the appropriate conversion. This can be done by reversing the initial conversion formulas.

• µm = mils ÷ 0.03937
• µm = oz/ft² ÷ 0.02316
• µm = g/m² ÷ 7.067

For example, if a weight of 2 oz/ft² is required, but the only information that we have is that the coating weighs 650 g/m², we can get µm by dividing 650 by 7.067 (µm = 91.98). Now that we know µm is 91.98, we can solve for oz/ft² by multiplying 91.98 by 0.02316 (oz/ft² = 2.13). Since 2.13 oz/ft² is greater than the required 2 oz/ft², we now know that we have met the coating weight requirement. Work shown below:

• 650 g/m² ÷ 7.067 = 91.98 µm
• 91.98 µm x 0.02316 = 2.13 oz/ft²

A full list of conversions is provided below:

• µm = mils ÷ 0.03937
• µm = oz/ft² ÷ 0.02316
• µm = g/m² ÷ 7.067
• mils = µm x 0.03937
• mils = oz/ft² ÷ 0.2316 x 0.03937
• mils = g/m² ÷ 7.067 x 0.03937
• oz/ft² = µm x 0.02316
• oz/ft² = mils ÷ 0.03937 x 0.02316
• oz/ft² = g/m² ÷ 7.067 x 0.02316
• g/m² = µm x 7.067
• g/m² = mils ÷ 0.03937 x 7.067
• g/m² = oz/ft² ÷ 0.02316 x 7.067

The AGA provides the following charts to further simplify. Be aware that these charts are meant to provide general information and should not be used for precise calculations.