Studying US contract law you will probably learn that consideration must be “sufficient. ”  But this does not mean that there must be “enough”  consideration.  Consideration must be “legally” sufficient.

The general rule in the US is that courts don’t worry about the amount of consideration.  For example, if David offers to clean Patty’s car for $75 a court probably won’t worry about whether the job is worth more or less money.  As long as no deception was involved it probably won’t matter if Patty should have paid $10 or $100.  Court don’t usually concern themselves with the amount of consideration.

But courts will worry about legally sufficient consideration.  For example, past consideration is not legally sufficient consideration. If David gives Patty an apple on Monday as a present and Patty is so happy she says she’ll give David a pear the following day, there is no contract.  Patty does not have to give David a pear on Tuesday.   Patty and David did not agree to give a pear in exchange for an apple.

Below is an older video on an example of legally insufficient consideration: