If all the Ice Melted

Before this discussion starts we need to lay down some basic facts.

The oceans occupy 361 million square kilometers ( 361 x 106 km²) of the Earth’s surface.
The volume of ice in Antarctica is approximately 25,300,000 km³
(Area = 13,829,430 km² & average thickness is 1.829 km)
The volume of ice in Greenland is about approximately 2,500,000 km³
Approximate amount of ice on the whole planet would be about 30,000,000 km³
One metric tonne of water has a volume of one cubic meter (1 tonne water ≡ 1 m³)
One gigatonne of water has a volume of one billion cubic meters, or one cubic kilometer.(1 Gt water ≡ 1 km³)

Of course, one gigatonne of ice has a greater volume than one gigatonne of water. But it will still have a volume of 1 km³ when it melts.

So then how many gigatonnes of ice must melt to raise the oceans one millimeter (10^-3 meters)?

1 mm / (2.78 microns / Gt) = 10^-3 m / (2.78 x 10^-6 m / Gt) = 360 Gt.
(From 1 GT gives: 1 km³ / 361 x 10⁶ km² = 2.78 x 10^-6 meters = 2.78 microns)

So 360 km³ of water will raise the oceans 1 mm.

The average density of glacial (packed) ice is about 850 kg per cubic meter so for any ice to water conversions we multiply by about 0.85

So 30,000,000 km³ gives about 25.5 million Gigatonnes of Water.

So if all the ice on the planet melted this would give a total rise of 70.8 meters.

How bad is it for us then?

Velicogna (Science, vol 311, 2006) used time varying gravity measurements from the GRACE satellites estimated that Antarctica was losing 152 km3 of ice per year. This is equivalent to 0.4 millimeters of global sea-level rise per year. One hundred years at this rate would add a massive 4cm to the oceans. (Deliberately selected because Science is so biased towards AGW)

It would take about 200,000 years for all the ice to melt, assuming no ice ages etc. in the mean time.