Share this on Facebook
download .zip with all pictures
The size shouldn’t make a big difference. The A380 has to carry a bunch of passengers plus the fuel, with most of the weight going to the passengers.
An A380 apparently has a [fuel capacity of 250 tons](http://forums.jetphotos.net/showthread.php?t=51684), and burns about [12 tons per hour](http://www.pprune.org/tech-log/487325-a380-fuel-burn-hr-very-rough-numbers.html), which gives it a range of about 20 hours.
The KC-135 carries 200 tons of fuel so if it could use that fuel for its own engines, the only way it could possibly have a shorter range than the A380 is if it burned fuel at roughly the same rate as the much bigger A380.
My guess is that either it can’t use the fuel it carries for its own engines (which seems like a strange design choice) or they so rarely bother with that (because the range is so huge anyhow) that they don’t bother quoting that figure.