A precise answer is impossible, since a number of variables affect wireless installations. At one time long ago, Apple used to publish range specifications. They no longer do, for this very reason.
Here is what they say today:
Actual performance will vary based on range, connection rate, site conditions, size of network, and other factors. Range will vary with site conditions.
... this itself is odd, since it implies that they at least provide an estimate of range, which they do not.
In ideal conditions with no interference, intervening objects, or competing wireless networks, you can expect a maximum range of about 100m. The presence of any of these sources of interference will reduce this range. If you live in an area with many other wireless networks, or your AirPort is behind several brick or stone walls, you may only get 15 - 20 m, perhaps even less.
The only way to determine its actual range is to use one.