Difference between below and under

Both below and under can mean ‘lower than’.

• The knives are in the cupboard under the sink. OR The knives are in the cupboard below the sink.

Below is preferred when one thing is not directly under another.

• The sun disappeared below the horizon. (NOT The sun disappeared under the horizon.)
• The climbers stopped several hundred meters below the top of the mountain.

Under is preferred when something is covered by what is over it.

• He was wearing a blue shirt under his sweater.
• The cat is under the bed.
• The whole village was under water.

In measurements of temperature and height we use below.

• The temperature is five degrees below zero.
• Parts of the city are below sea level.

To mean ‘less than’ or ‘younger than’ we use under.

• There were under ten students in the class. (NOT There were below ten students in the class.)
• You can’t get a driving license if you are under 18. (NOT You can’t get a driving license if you are below 18.)

Notes
There is a similar difference between above and over. Above is used in measurements of temperature and height.
Over is used to express ideas such as ‘older than’ and ‘more than’.

• You have to be over 18 to see that film.

Please share this with others if you feel it's helpful.