Not quite, Ladylush - if only it were that simple!
The exact amount you would need to put in is undefinable. If you retire at a bad point in the market you can't guarantee a thing. which is why so many people with DC pensions are currently saying they can't afford to retire.
The thing is, pension schemes used to be a "gratuity" - a kind, paternalistic thing your employer did for long-standing employees to help them in the short period between retirement and death. These days we live for unpredictably long periods, the government has meddled with the tax treatment of schemes and put layers and layers of regulation over what used to be a simple act of generosity. So DB pensions are prohibitively expensive to provide, which is why you won't come across new schemes these days. In fact, all you ever hear about are scheme closures (i.e. shutting to new joiners) and schemes being frozen (no more accrual for anyone, and existing members switching to a less generous scheme for future service).
Some people in the private sector do have decent pensions but I expect most of them will be shuffling off into retirement in the next few years. The key difference though is the cost. The NHS schemes particularly are going to be quite a burden on the taxpayer. When you consider how many people have worked in the NHS in the last however many years (the NHS is huge!), each of them accruing benefit which cannot be taken away once accrued and the fact that the NHS schemes (all of them, I think, but am not 100%) are unfunded so that the bill goes to the taxpayer as and when each person retires (so there is no investment, planning etc) you can see that the cost could be quite a drain. I would rather see these pension schemes reined in than even more taxes being raised to foot the bill.
Ros Altmann, who is even more of a pensions geek than me, published some figures here a couple of years ago which make me break out in a cold sweat.
Again, not having a go at public sector workers, but the pension arrangements for much of the public sector really are quite different from the rest of us.
God, I really am a geek.