How big is an acre?

Day 4: Area Units - and Acres

Acres are most commonly used to measure land and they are different sizes depending on the system of units being used. Measuring land with acres began during the middle ages and one acre was the amount of land one person could plow with oxen in one day. Since it was time consuming to turn the oxen around, the plots were typically rectangular measuring 22 feet x 220 feet.

One acre is slightly smaller than a football field and near 70 feet x 70 feet when measured as a square. Land in the United States is measured in acres. There are 16 sets of  40 acre plots in one square mile as represented by the figure below. The highlighted grey square represents 40 acres in one square mile.

Acres are used to measure land today because they are convenient units. One acre is equal to .0015625 square miles and 4840 square yards. Therefore, using square miles or square yards would result in very large or very small numbers when discussing personal property.

As done on the previous day with distance, the kids first made a list of all the area units they were familiar with. I was surprised that they only wrote square inches. So we had a review and they caught on quickly.


square inches
square feet
square yards
square miles

The pattern of feet to square feet and so on became obvious quickly, and we also made a list of metric units as well.

Then we stepped outside to determine how big an acre was by measuring the field behind our house.

We will always remember that it is about 3 acres in size.

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