Almost impossible to calculate due to the way annuity rates move etc.
Saw a newspaper article the other day that suggested your total contribution (yours and employers) should equal half your age. So a man of 30 should be contibuting 15% of earnings.
A friend of mine has another way to look at it. Assume you will work for 40 years and will enjoy a 20 year retirement thereafter. If you want a two thirds pension for 20 years, you need to contribute one third of income for 40 years.
LJ