Enter the total number of atoms of the molecule (atoms) and the mass per molecule (AMU) into the Exact Mass Calculator. The calculator will evaluate and display the Exact Mass. 

Exact Mass Formula

The following formula is used to calculate the Exact Mass. 

EM = #A * MM

  • Where EM is the Exact Mass (AMU)
  • #A is the total number of atoms of the molecule (atoms) 
  • MM is the mass per molecule (AMU) 

How to Calculate Exact Mass?

The following example problems outline how to calculate Exact Mass.

Example Problem #1:

  1. First, determine the total number of atoms of the molecule (atoms). 
    • The total number of atoms of the molecule (atoms) is given as: 3.
  2. Next, determine the mass per molecule (AMU). 
    • The mass per molecule (AMU) is provided as: 12.
  3. Finally, calculate the Exact Mass using the equation above: 

EM = #A * MM

The values given above are inserted into the equation below and the solution is calculated:

EM = 3 * 12 = 36 (AMU)


Example Problem #2: 

For this problem, the variables needed are provided below:

total number of atoms of the molecule (atoms) = 8

mass per molecule (AMU) = 6

This example problem is a test of your knowledge on the subject. Use the calculator above to check your answer. 

EM = #A * MM = ?