What exactly counts as “within X squares” in DnD 4e

Question

The cleric attack Blessing of Wrath is a melee attack, but it also allows one ally within 5 squares of me to get a power bonus to their next damage roll against the target.

What counts as "within 5 squares" in DnD 4e? Is it the same as the rules for burst or area attacks? Is it anyone within an 11-by-11 square centred on me? Or a rough circle? Does cover or terrain affect it at all? Can it go around corners?

Answer 1

This is a range issue, so we turn to the Rules Compendium's entry on range:

To determine the range between a power's user and its target, count the distance between them as normal (see "Determining Distance," page 201), including 1 square that the target occupies. (RC 107)

Here's that "Determining Distance" reference:

To determine how far away one square is from another, start counting from any square adjacent to one of the squares (even one that is diagonally adjacent but around a corner), then count around blocking terrain and end up in the other square. Make sure to use the shortest path. (RC 202)

Note that it makes no mention of difficult terrain or cover, just blocking terrain. So yes, you can consider it like a burst with a single target, for the purposes of determining valid targets.

Of course, you also need line of effect:

When there is a clear line from one point to another in an encounter, there is line of effect. Unless otherwise noted, there must be line of effect between the origin square of an effect and its intended target for that target to be affected. (RC 107)

Answer 2

Anyone within an 11-by-11 square centered on you is considered to be within 5 squares of you; note that you must also have line of effect to the ally to give them the bonus.

Basically, if you put a chess king on your square, can it reach your ally's square in 5 moves? If so, that ally is within 5 squares of you.

Line of effect is required to affect anything unless the power explicitly says it is not required (this is very rare, almost entirely limited to a handful of self-teleportation abilities). From the Rules Compendium, p107:

Line of Effect: ... Unless otherwise noted, there must be line of effect between the origin square of an effect and its intended target for that target to be affected. ...