Ways To Gauge
The eyes don't lie
Although he may be trying to play it cool, if he's interested, his eyes won't be able to help but creep into your direction from time to time. You may also find when you talk to him that he is firm about holding eye contact with you. Although he may look away if he suddenly feels embarrassed or silly, for the most part, he will maintain your gaze for as long as you are willing.
He asks others about you
Old elementary school habits die hard. Though he may be a mature man (for the most part), coming right up to you and asking if you are available and want to go on a date with him is an intimidaing thing to do. To test the waters, he may ask some of your friends if you are seeing anyone, or he may simply show a heightened interest when you come up in conversation. It's no guarantee, but finding out he's been asking about you is almost certainly a good sign.
Check out his body language
No matter how cool he may be trying to play it in his head, much like the eyes, the body doesn't lie. If he feels a connection with you, his body may want to face in your direction — even when he's on the other side of the room. He wants to see you, and he also wants you to notice him, so he'll avoid turning his back to you whenever possible. You may also find that he lingers near you more than is strictly necessary. For instance, even if he is on his way home, you may find he stops to have a conversation with someone in an area near you. In some ways, men are like peacocks: They want you to notice them, and they may be willing to stand around until you do.
He shows interest
If he feels a spark with you, you may notice that he shows an increased interest in subjects you say you are passionate about. For instance, if you tell him what your favorite movie is, he may report back later that week that he watched it and loved it as well. If it seems as though he is making an effort to talk with you more, he is likely very interested.
Although some men are worried about coming on too strongly in a work environment or among friends, once he's established a good camaraderie with you, he may begin showing increased signs that he is interested. He may touch your shoulder as he laughs or graze your back as he moves past you to get somewhere. Physical contact could mean he is simply comfortable around you, but in many cases, it indicates he is ready for your relationship to be something more.