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.)
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.