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

One of our favorite websites, Wolfram |Alpha does online dynamic computations based on a vast collection of built-in data, algorithms, and methods.