# Conversion Formulas

What’s the formula to convert mg/L to ppm?

1 mg/L = 1 ppm for dilute aqueous solutions. For example, a chlorine concentration of 1.8 mg/L chlorine is equivalent to 1.8 ppm chlorine.

How can I convert percent transmittance to absorbance, or absorbance to percent transmittance?

To convert a value from percent transmittance (%T) to absorbance, use the following equation:

• Absorbance = 2 – log(%T)
• Example: convert 56%T to absorbance:
• 2 – log(56) = 0.252 absorbance units

To convert a value from absorbance to percent transmittance, use the following equation:

• %T = antilog (2 – absorbance)
• Example: convert an absorbance of 0.505 to %T:
• antilog (2 – 0.505) = 31.3 %T

What is a grain per gallon (gpg)?

One grain is equivalent to 64.799 milligrams. It’s a historic unit of weight once used for barleycorn. A grain per gallon is the weight of a substance in one gallon of water, similar to a milligram per liter.

What’s the formula for converting grains per gallon (gpg) to milligrams per liter (mg/L)?

Multiply gpg by 17.1 to get mg/L (1 gpg = 17.1 mg/L). For example, a hardness test result of 3 gpg as CaCO3 is equivalent to 51 mg/L as CaCO3. What’s the formula for converting grains per gallon to milligrams per liter? 1 grain = 64.799 milligrams 1 gallon = 3.785 liters 64.799 divided by 3.785 liters = 17.1 1 gpg = 17.1 mg/L

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