(Number of reckonable contributions or credits) / 2080 x 100 gives the percentage of the full rate contributory pension to which one is entitled. (Maximum 100%).
E.g. say you have 1,659 reckonable contributions/credits then that means 1659 / 2080 x 100 =~ 80% of the full pension.
You can get your PRSI contribution statement from myWelfare:
<p>Make a repayment, or apply for a payment statement, contribution statement or PRSI refund</p>
services.mywelfare.ie
And there are loads of existing threads on ways to maximise your PRSI contributions/credits if you otherwise risk being short of the 2,080 figure at retirement age.