Which dishwashing liquid is the better buy?

$$ Dishwashing Liquid A contains $12$ ounces and costs $$4\mathrm{.}00$

$$ Dishwashing Liquid B contains $16$ ounces and costs $$6\mathrm{.}50$

Imagine that you are faced with this decision at the store and you do not have your phone or even a pencil and paper $$ the only tool you have is your ability to reason.