If the concentrate is mixed to the instructions on the can, (it's usually 3 parts water, 1 part concentrate) the resulting juice should wind up between 1.040 and 1.050. Most likely really close to 1.045, at least according to the various apple concentrates I've messed with.
So 14 cans * 12oz * 4 volumes each = 672oz or 5.25 gallons. If that's a 6 gallon carboy you've got there, you've got plenty of space! Eight 12oz cans would top it off.
If you did that... 672oz now * 1.045 est. og + 8 more cans concentrate * 12oz each * 1.180 est. sg of concentrate = 815.52 -- Divided by 6 gallons or 768oz, gives an estimated resulting effective original gravity of 1.062, if you'd started out this way. Just a guess. YMMV.
If you're feeling empirical, pick up an extra can of the same brand you've been using, mix up a pitcher, and plop in the hydrometer to see where it winds up. That'll tell you anything you can know at this point. Then, for a 3/1 water/concentrate ratio, subtract 1 from the resulting sg, multiply the remainder by 4, then add the 1 back to the result to get the gravity of the concentrate. IE, 1.045 juice started out as 3 cans of 1.000 water and one can of 1.180 concentrate.