The same sound is more intense if you hear it in a smaller area. In general, we call sounds with a higher intensity louder. We are used to measuring the sounds we hear in loudness. The sound of your friend yelling is loud, while the sound of your own breathing is very soft. Loudness cannot be assigned a specific number, but intensity can.
Intensity is measured in decibels.
The human ear is more sensitive to high sounds, so they may seem louder than a low noise of the same intensity. Decibels and intensity, however, do not depend on the ear. They can be measured with instruments. A whisper is about 10 decibels while thunder is 100 decibels. Listening to loud sounds, sounds with intensities above 85 decibels, may damage your ears.