This lesson provides students with an opportunity to practice measuring weight and volume in the metric and customary systems. The metric system is based on units of ten and is used globally, while the customary system is used primarily in the United States. Estimation is an important skill for making rough calculations when precise measurement isn't practical. Students should be able to estimate both capacity (volume) and weight using metric and customary units.
The materials for this lesson are easily obtained; most can be pulled from recycling bins or found at a grocery store. Empty food containers like cereal boxes, cottage cheese tubs, and beverage bottles are the least expensive math manipulative you can find! Plastic and metal containers should be washed before use (do not use packaging that contained raw meat; it can spread unwanted bacteria). In this lesson, students' experience measuring the weight and volume of food items will help them gain an understanding of how estimation and measurement skills are used on the farm.
Being able to measure in a variety of ways is a valuable life skill. How many times a day are we asked, or do we ask, “How much?” “How big?” “How far?” Many of our measurements are based on methods that people used before we had standardized devices like yardsticks and rulers. Horses were measured according to how many hands high they were. A yard of fabric was the length of the merchant’s outstretched arm, measured from their nose to the tip of their thumb. A foot was the length of an average person’s foot. Agricultural products like vegetables and grains are measured in bushels, equivalent to about 35.2 liters. Today, measurements have been widely standardized. A foot or a meter means the same thing everywhere.
Whether you are a student buying an apple for lunch or a farmer selling wheat, you need a way to measure whatever it is you are buying or selling. The cashier at the grocery store probably will weigh your apple to determine how much to charge you. The amount of money a farmer receives for their wheat will depend on how many bushels he or she has produced. Some products are sold according to their weight or how heavy they are on a scale. Other products are sold according to volume, which is the space the item takes up in cubic units. Liquid products like milk or juice might be sold by the pint, gallon, or liter. Some food products are priced by the piece no matter how big they are, like cucumbers sold two for $1.00 or red peppers sold for $1.50 each.
Most of the produce you buy in the grocery store—apples, peaches, onion, potatoes, tomatoes, squash, etc.—is sold by the pound. But if you go to a farmer's market or buy the same produce from roadside stands, you may pay for it by the bushel or half-bushel basket. Smaller quantities are measured in quart or pint baskets. Most berries—raspberries, strawberries, blueberries, etc.—are sold by the pint or by the quart. Corn on the cob is generally sold by the dozen. Pumpkins are sorted according to size—miniature, small, medium, large, jumbo. Each pumpkin in a category will cost the same.
The price of a beef steer depends on how much the steer weighs. When a steer is sold, it is weighed on a large livestock scale. The weight is then multiplied by the current market price. If the current market price is $1.50 per pound, and the steer weighs 770 pounds (carcass weight), the value of the steer would be $1155. Market prices are determined by how much of a product is available for sale, how much people are willing and able to pay for the product, and other supply and demand factors.
Wheat farmers sell their wheat by the bushel which weighs 60 pounds. Like beef, the price of wheat per bushel depends on the current market value. Oats, barley, feed corn, rye, and soybeans are also sold by the bushel. However, the seed the farmer purchases for replanting is priced by the pound. Garden seeds and herbs are sold by the ounce because most gardeners do not need large quantities. There are many units of measurement to fit different needs. Sometimes small units work better than large units, and sometimes it is more convenient to measure volume than to measure weight. In this lesson students will learn measurement and estimation skills using a variety of tools and agricultural products.