Enter the theoretical and experimental mass values into the calculator to determine the mass error in parts per million (ppm).

Mass Error Formula

The following formula is used to calculate the mass error:

\text{Mass Error (ppm)} = \left( \frac{\text{Experimental Mass} - \text{Theoretical Mass}}{\text{Theoretical Mass}} \right) \times 10^6


  • Theoretical Mass (Da) is the mass of a molecule as calculated from its formula.
  • Experimental Mass (Da) is the mass of a molecule as determined by a mass spectrometer or other experimental methods.
  • Mass Error (ppm) is the difference between the experimental and theoretical mass values, expressed in parts per million.

To calculate the mass error, subtract the theoretical mass from the experimental mass, divide by the theoretical mass, and then multiply by one million to convert to parts per million (ppm).

What is Mass Error?

Mass error is a measure of the accuracy of a mass spectrometry measurement. It quantifies the difference between the measured mass of an ion and its calculated theoretical mass based on its elemental composition. Mass error is typically expressed in parts per million (ppm) to provide a unit that is independent of the ion’s mass, allowing for comparison across different mass ranges.

How to Calculate Mass Error?

The following steps outline how to calculate the mass error:

  1. First, determine the theoretical mass (Da) of the molecule.
  2. Next, determine the experimental mass (Da) measured by the mass spectrometer.
  3. Use the formula to calculate the mass error (ppm).
  4. Finally, compare the calculated mass error with the mass spectrometer’s specifications to assess the accuracy of the measurement.
  5. After inserting the variables and calculating the result, check your answer with the calculator above.

Example Problem:

Use the following variables as an example problem to test your knowledge.

Theoretical Mass (Da) = 196.083

Experimental Mass (Da) = 196.078