# Mass calculations: mass error and m/z from formula

This page allows you to perform three calculations:

- The mass error of an assignment, when comparing a theoretical m/z and an experimentally observed m/z.
- The theoretical m/z of the monoisotopic peak for a given molecular formula.
- The m/z range for an m/z of interest plus/minus a specified error in ppm.

When calculating the theoretical m/z, remember to include the charge carriers (e.g. add or remove hydrogen atoms and adjust the charge accordingly, to simulate gain or loss of protons) and to use a positive value or negative value for the charge.

If there are specific elements that are not present in the list below and which you'd like to see added, let me know.