Checking how hard and big your penis is can help you tell if you're fully erect. Your penis should feel harder and bigger when it's fully arched than when it's flat. Also, it should be completely filled with blood, which will make it much bigger and stiffer. The slope of your erection may also change, but it will usually point up. It's also possible that your genitalia will feel more aroused and sensitive. It's important to remember that the strength of an erection can be different for each person and depend on things like age, physical health, and level of excitement. Should you have doubts about the quality of your erections or if you have ongoing problems getting or keeping an erection, you might want to talk to a doctor or nurse for more information.