Blog: Price Elasticity of Demand

Price Elasticity of Demand
 

The Price Elasticity of Demand (commonly known as just price elasticity) measures the rate of response of quantity demanded due to a price change. The formula for the Price Elasticity of Demand (PEoD) is:
PEoD = (% Change in Quantity Demanded)/(% Change in Price)

Calculating the Price Elasticity of Demand

You may be asked the question "Given the following data, calculate the price elasticity of demand when the price changes from $9.00 to $10.00" Using the chart on the bottom of the page, I'll walk you through answering this question. (Your course may use the more complicated Arc Price Elasticity of Demand formula. If so you'll need to see the article on Arc Elasticity)
First we'll need to find the data we need. We know that the original price is $9 and the new price is $10, so we have Price(OLD)=$9 and Price(NEW)=$10. From the chart we see that the quantity demanded when the price is $9 is 150 and when the price is $10 is 110. Since we're going from $9 to $10, we have QDemand(OLD)=150 and QDemand(NEW)=110, where "QDemand" is short for "Quantity Demanded". So we have:

Price(OLD)=9
Price(NEW)=10
QDemand(OLD)=150
QDemand(NEW)=110

To calculate the price elasticity, we need to know what the percentage change in quantity demand is and what the percentage change in price is. It's best to calculate these one at a time.

Calculating the Percentage Change in Quantity Demanded

The formula used to calculate the percentage change in quantity demanded is:
[QDemand(NEW) - QDemand(OLD)] / QDemand(OLD)

By filling in the values we wrote down, we get:

[110 - 150] / 150 = (-40/150) = -0.2667

We note that % Change in Quantity Demanded = -0.2667 (We leave this in decimal terms. In percentage terms this would be -26.67%). Now we need to calculate the percentage change in price.

Calculating the Percentage Change in Price

Similar to before, the formula used to calculate the percentage change in price is:
[Price(NEW) - Price(OLD)] / Price(OLD)

By filling in the values we wrote down, we get:

[10 - 9] / 9 = (1/9) = 0.1111

We have both the percentage change in quantity demand and the percentage change in price, so we can calculate the price elasticity of demand.

Final Step of Calculating the Price Elasticity of Demand

We go back to our formula of:
PEoD = (% Change in Quantity Demanded)/(% Change in Price)

We can now fill in the two percentages in this equation using the figures we calculated earlier.

PEoD = (-0.2667)/(0.1111) = -2.4005

When we analyze price elasticities we're concerned with their absolute value, so we ignore the negative value. We conclude that the price elasticity of demand when the price increases from $9 to $10 is 2.4005.