Ask your child to compare different objects around the house such as a crayon and a coat. Place the objects together. Have the child use the smaller object to measure the larger one. For example, he will place the crayon at the bottom of the coat while the coat is on the floor. Ask him how many crayons is it from the bottom of the coat to the top. The child will use the crayon to measure it. Use the crayon to measure other things such as the width of a door or the height of a bookshelf.
Children will use their feet and fingers to measure objects and distances. Have your child walk heel-to-toe the distance from her bed to her doorway. She will slowly walk the distance using her feet. Ask her to write the number down and compare the distance from the kitchen to the living room. She will then measure by walking. Smaller objects are measured with fingers. Choose a particular finger such as the thumb. Compare the measurements of objects with a child's thumb and an adult's thumb.
Give your child a simple ruler with clear markings to observe. Ask him what all the marks are and why some lines are thicker than others. Children need some time to get a sense of a tool and he should be given time to try out the ruler. Explain to the child that the ruler is read from the left to the right and 1 inch is a standard measurement. It is always the same, unlike a thumb that will grow larger. Have the child count out the marks between the numbers.
With the ruler in hand, have your child measure things around the house. Remeasure objects and distances that were first measured with feet and fingers. Have your child estimate measurements before using the ruler. Also ask your child to help you measure a real household project such as putting up curtains or finding the correct screws. Using a home repair project teaches the real-world value of measuring with a ruler, and your child will learn how to measure correctly.