Ocean height by 2100

So im not sure exactly how high the seas will rise if the ice sheets of Antarctica and the Arctic continue to melt by 2100. My best guess would be a rise of about 3-5 feet. Would that seem reasonable. Its just this whole 50 foot increase doesnt really make sense in that time frame that ive heard from global warming webites. I mean i understand the Earth is warming but its not arming at the extreams they said. Plus in certin areas there have been cooler than average temperatures. Any thoughts?