This is somewhat dependent on manufacturer and the quality of the helmet sold, which can vary a lot.
For the USA, there is the Bicycle Helmet Safety Institute which does various tests and gives information.
For bike helmets to be legal in the US, they are required to pass a test of being dropped between one and two meters on an anvil.
All of the standards discussed here require the helmet to pass a lab
test where it is placed on an instrumented headform, turned upside
down and dropped for a measured distance onto an anvil. The anvil can
be flat, round (hemispheric) or another shape like a curbstone, a
skate blade or a horse's hoof. Drop distances vary but are generally
between one and two meters (3.3 to 6.6 feet).
Their guidelines about when to replace a helmet mention say little about a short drop on a floor.
You can also crack the helmet foam or damage it by dropping the helmet
on a hard surface. The cracks may be small and hard to see, so you
need to look carefully. Cracks in the foam always require replacement
of the helmet.
So, look for visible cracks very carefully.
Did you crash it? Replace!
Did you drop it hard enough to crack the foam? Replace.
Is it from the 1970's? Replace.
Is the outside just foam or cloth instead of plastic? Replace.
Does it lack a CPSC, ASTM or Snell sticker? Replace.
Can you not adjust it to fit correctly? Replace!!
Do you hate it? Replace.
I wouldn't think that a short drop would have enough force to render the helmet ineffective as a protection device. Going by the BHSI guidelines, unless there is visible damage or it was dropped from a great height, the helmet should not need to be replaced.