The textbook range and its edges
The commonly stated range of human hearing is 20 Hz to 20,000 Hz. That spans about 10 octaves, and it's a nominal figure. People vary, especially at the top. Under ideal lab conditions, people have heard tones as low as 12 Hz and as high as 28 kHz.
Below 20 Hz is infrasound, and above 20 kHz is ultrasound. Other animals can use them. Some whales can hear infrasound as low as 7 Hz.
Why your own range is narrower
The upper limit drops with age, and a gradual loss of sensitivity to higher frequencies is normal. In adults the hearing threshold rises sharply at 15 kHz, so the top of the range is the first part to fade. A sine tone sweep shows where your own edge is: step upward until the tone disappears.
Start quiet and raise the volume slowly. A pure tone at a high level can hurt your ears and damage a tweeter.
Loudness depends on pitch
The ear isn't equally sensitive everywhere. It's most sensitive between 2000 and 5000 Hz, and equal loudness contours show it needs more sound at the low and high ends to hear a tone as equally loud. A tone at 3000 Hz is easy to hear at a low volume, while a tone at 30 Hz takes much more.
Wavelength tells the other half of the story. A 20 Hz wave is 56 feet (17.1 meters) long in air. That's longer than most rooms. Small speakers often can't move enough air to play the lowest tones, so a silent 20 Hz test can be about the speaker, not your ears.
When a low tone isn't really low
If you hear a very low tone from a laptop or a small speaker, you might be hearing its harmonics instead. A square wave at 20 Hz has odd harmonics at 60 Hz and 100 Hz, which are easy to hear. A speaker that isn't perfectly linear adds harmonics to a sine too.
Test the low end with a sine wave, and use a few different speakers or headphones before you decide what you can't hear.