All th emajor manufacturers make claims about their range which don't always stand up to reality. Other factors come in and reduce the range anyway so it's probably better and more reliable to daisy chain some equipment along your planned route.
As I recall the real range indoors is likely to be 50 feet or thru five walls (or is it less).
Manufacturers test using line of sight, very unlike at home.
I would see if you can optimise your reception and avoid interference.
1) raise the router above furniture level
2) Experiment with channels (some will work better or worse depending on your environment)
3) If you can detect strong neighbouring wifi, use a channel 5 stops away from strongest.
4) Relocate cordless phone base or video sender etc.
5) Be prepared to move the computer (or at least turn it so your body is not between the router signal and the wireless adapter's antenna.