Enter the mass before decay (kg) and the mass after decay (kg) into the calculator to determine the Decay Energy. 

Decay Energy Formula

The following equation is used to calculate the Decay Energy. 

E = (M1-M2) * c^2


  • Where E is the Decay Energy (Joules)
  • M1 is the mass before decay (kg) 
  • M2 is the mass after decay (kg) 
  • c is the speed of light (299792458 m/s)

How to Calculate Decay Energy?

The following two example problems outline the steps and information needed in order to calculate the Decay Energy.

Example Problem #1:

  1. First, determine the mass before decay (kg). In this example, the mass before decay (kg) is measured to be 50.
  2. Next, determine the mass after decay (kg). For this problem, the mass after decay (kg) is calculated to be 20.
  3. Finally, calculate the Decay Energy using the formula above: 

E = (M1-M2) * c^2

Inserting the values from above and solving the equation with the imputed values gives: 

E = (50-20) * 299792458^2 = 2.69 e+18 (Joules)

Example Problem #2: 

Using the same process as example problem 1, we first define the needed variables outlined by the formula. In this case, the values are provide as: 

mass before decay (kg) = .000024

mass after decay (kg) = .000012

Entering these values into the formula or calculator above gives us: 

E = (.000024-.000012) * 299792458^2 = 1.0785 e+12 (Joules)