In order to estimate units of measure and to help us visualize their amounts, we use benchmarks. A benchmark is a common object that helps us remember the measure. Most Americans know how much two liters is because they picture a two liter soda. If we can get our students to associate real world objects to units of measure, they will learn the units.
In this powerpoint I have included customary and metric benchmarks for linear, weight/mass, capacity, time and temperature units of measure.