A three meter key would need a huge lock, lets go with three centimeters that can be carried on a chain or in a pocket.
meters
3 centimeters three meters would b like _________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________...
Most locks have keys that are small enough to fit into the pocket. As such, a key is about 3 centimeters long.
My house key is 0.95 of 5.8 centimetres.
The standard dimensions of a piano key are typically around 23-28 centimeters in length and 2-2.5 centimeters in width.
Probably Centimeters
Length is a fundamental physical quantity that represents the measurement of a straight line from one point to another. It is typically measured in units such as meters, centimeters, or inches, and is a key parameter in describing the size and dimensions of objects in the physical world.
I would use inches or centimeters, or millimeters to measure this.
I would use centimeters.
I just measured two housekeys...one was 5.3cm and the other was 5.5cm, so I suppose you could say a house key is approximately 5 centimeters in length.
Keys come in many sizes. I have a travel case key which is only 2 cm long, and an old fashioned 'house door' key which is 12 cm long.
maybe about 2 inches