A drop in the ocean. IDIOM.

a drop in the ocean 

Meaning: If an amount is a drop in the ocean, it's a very small portion of the amount that's needed.

For example:

Our government's sending a thousand tons of food, but that's just a drop in the ocean compared to what's needed.

I know twenty dollars is just a drop in the ocean, but if everyone gave that much it'd make a big difference. 

Note: The U.S. equivalent is "a drop in the bucket".

Variety: This idiom is typically used in British English but may be used in other varieties of English too.

Quick Quiz:

If something is described as being a drop in the ocean, it is

a small part of what's needed a huge part of what's needed all that's needed

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PICTURE SOURCE: newenergyworldnetwork.com