Batch sparging is generally considered faster. Easier? debatable. Most new brewers prefer batch sparging. Grain absorption is approximately 0.125 gal/lb of grain. Deduct that amount from your mash in volume. Now you know how much will be collected when you drain the tun the first time. But, you would like to collect half of the total volume for boil. So, subtract whats going to come out from the half boil volume. Now you know how much sparge water to add to the mash tun to get the first runnings to be half of the total. For five gallons, preboil total will usually be 6.5 gal. Now, drain the first runnings. Then, sparge with the second half volume, stir, wait 10 minutes, vorlauf (
www.homebrewtalk.com/wiki/index.php/Vorlauf) and drain the tun. That's it. easy peasy. Don't sweat the dead space unless you have a false bottom. Cheers...