You would measure the distance of the door with meters because liters measure volume not length.
by meters
A door is about 2 meters, but most likely you'd measure in centimeters.
Meters
centimeters
meters.
It can be measured in meters or feet and inches.
meters
Centimetres.
meters
Typical height is 80 inches.
You calculate the area of any rectangle by multiplying height by width. Simply measure the height and width in meters, multiply, and the result will be in square meters.