The fourth grade is usually when most students are introduced to different measurement systems. One of the systems they need to understand is referred to as customary units of capacity--the system to measure liquids in the United States. The customary units of capacity include the gallon, quart, pint, cup, and fluid ounce. Fourth-grade students need to understand how much liquid fits into each container as well as how to convert between each measurement.


The largest unit of customary measurement that fourth-graders need to understand is a gallon. Most teachers relate the size of a gallon to the large milk jugs that are bought at grocery stores. Almost all students have these at home or have seen them in the stores. However, some students may not have any experience with these jugs and it is important that the teacher bring in a milk jug for the students to actually see and touch. This will ensure that they don't confuse it with the smaller cartons of milk.


A quart is the next largest unit of customary measurement that fourth-grade students need to understand. Students need to learn that four quarts will fit into one gallon. Many teachers will bring a Powerade bottle or motor oil jug into the classroom to give the students a good representation of how much liquid fits into one quart. The teacher may also fill up the gallon milk jug with four quarts of water to demonstrate how to convert quarts to gallons.


A pint is the middle unit of capacity that fourth grade students need to understand. There are two pints in every quart and eight pints in every gallon. This is generally the hardest unit of measurement for students to understand because it is in the middle. Teachers can bring in empty pints of ice cream to show students how much liquid will fit into a pint and use it to fill up the quart jug as well as the gallon milk jug.


A cup is the second smallest unit of capacity in customary measurement. There are two cups in every pint, four cups in every quart, and 16 cups in every gallon. A cup can be understood by showing fourth-graders an actual measuring cup or a coffee cup. The teacher will usually fill up or let the students practice filling up the pint, quart, and gallon jugs to demonstrate how many cups fit into each container.

Fluid Ounce

A fluid ounce is the smallest unit of capacity that fourth-grade students need to understand in the customary measurement system. There are eight ounces in one cup, 16 ounces in one pint, 32 ounces in one quart, and 128 ounces in one gallon. An eye dropper container and the plastic cup that comes with most cough syrups is about one fluid ounce. Students can practice converting between ounces and other units by filling up the other containers using the fluid ounce container.

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