A millivolt, or mV, is a unit of measurement equal to one-thousandth of a volt. Ppm refers to parts per million, and is a way to describe dilute concentrations of a substance -- usually in soil or water. Converting between one unit and another poses challenges by hand, because of the miniscule decimals involved; one millivolt is equal to 11.000000e-03 PPM. An online calculator can help you convert between the two units in a snap.
Navigate to the Free University's Conversion of Units Calculator.
Scroll down to mV in the "From" scroll box and then click "mV."
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Scroll down to the "To" scroll box and then click "ppm."
Type the number of mV you want to convert into the "From" text box and then click "Submit." The result will appear on the first line in a new page. For example, 99 mV converted to ppm results in 9.900000e-02.
You can also use a regular calculator for the conversion. Multiply the number of mV by 1.000000e-03.