Meters or feet would be best, depending on where you live.
liters
A micrometre. A millimetre would be too big a unit but a tenth of a millimetre should do fine.
You can invent any number of nonstandard units, but none of them is "best". It is best to use standard units, that is, the meter.
The volume is best measured in millilitres still. The weight is the best approach for this. To measure size i.e. width in particular, a millimetre is a good unit to use.
You could use cm, meters (eg. 0.18cm ) or millimetres . A mix of cm and mm should be best for accuracy .
A caliper would be the best tool for measuring the width of a pencil lead. It is precise and allows you to measure small dimensions accurately.
Either 'inch' or 'centimeter' would do the job nicely.
Millimetres.
Answer: meters
liters
the metric system
best u nit to measure the length of bedroom = meter
Because of the dimensions involved, that would be measured in km. (kilometers).
A micrometre. A millimetre would be too big a unit but a tenth of a millimetre should do fine.
A millimetre.
The best tool to measure a lunch box would be a tape measure or a ruler, as they can provide accurate measurements of its length, width, and height. The most suitable unit of measure would be inches or centimeters, depending on your preference or regional standards. These measurements will help determine the lunch box's dimensions for storage or fitting into a backpack.
I would suggest putting the camera in front of the door to your bedroom. Putting the camera in the bedroom is not as safe as outside the bedroom. Also, putting the camera in front of the door would probably give you the best chance of seeing an intruders face.