Usually when measuring length, the meter is used

Usually when measuring length, the meter is used.

However, it depends on what you are measuring the length of. For example, if you were to measure the length of a basketball court, baseball field, football field, city block, etc., you would use the meter.

If you were measuring the distance (length) from one city to another, from the Earth to the Moon, or even from Earth to another planet, you would use the kilometer. The prefix kilo- means 1000, so there are 1000 meters in 1 kilometer. We generally measure larger distances in kilometers.

If you were measuring the length of something small, such as a the length of a person's foot, how thick a cellular phone is, etc., you would use a smaller unit. There are many to choose from, but the two that are used most often are the centimeter and the millimeter. Centi- means 1/100, so there are 100 centimeters in 1 meter. Milli- means 1/1000, so there are 1000 millimeters in 1 meter.

I added a video presentation about measurement -