# How do you find the average atomic mass?

Nov 11, 2015

When calculating the average atomic mass of an element you should be given the isotope and the percent abundance. For example (X is a made up element).

$X - 45$ = 44.8776 amu is 32.88% abundant.
$X - 47$ = 49.9443 amu is 67.12% abundant.

Note: amu stands for atomic mass unit

Given that information, you multiply the amu by the percent abundance

$.3288 \left(44.8776\right) = 14.75575$
$.6712 \left(46.9443\right) = 33.52261$

Then you add the two figures together to get your average atomic mass.

$14.75575 + 33.52261 = 48.27836$