With a tape measure.
probably to measure a lamp depending on if its a desk lamp or a stand up lamp, if you use a stand up lamp, i would suggest using either feet or inches
the trick to finding the right size lampshade for your lamp is to measure the base of the lamp, times it by the height and the divide it by the width. this answer will be the diameter of your lampshade.
To determine the right size lamp shade harp for your table lamp, measure the height of the lamp base and add 1 inch for a standard fit.
Probably centimeters, unless it's a really tall one (e.g. a street lamp), in which case meters would make more sense. Decimeters would be a sensible measurement here too, but nobody really uses those.
Just use a tape measure or some other measuring tool.
Centimetres.
The metric unit commonly used to measure height is the meter. So, you would measure the height of Big Ben in meters.
Kilograms. A lamp would typically weigh at around 10 kg
metres
that depends entirely on the size of the lamp post
ruler
that depends entirely on the size of the lamp post