This is perhaps the most important microeconomic concept that you will come across in your initial studies of economics.

The key is to understand the formula for calculating the coefficient of price elasticity, the factors that affect elasticity and also why elasticity is important for businesses when setting their prices.

What is the formula for calculating the coefficient of price elasticity of demand?

The formula for calculating the co-efficient of elasticity of demand is:

Percentage change in quantity demanded divided by the percentage change in price

Since changes in price and quantity usually move in opposite directions, usually we do not bother to put in the minus sign. We are more concerned with the co-efficient of elasticity of demand rather than the sign!

How much does quantity demanded change when price changes? By a lot or by a little? Elasticity can help us understand this important question.

What are the important values for price elasticity of demand?

We use the word "coefficient" to describe the values for price elasticity of demand

1. If Ped = 0 demand is perfectly inelastic - demand does not change at all when the price changes – the demand curve will be vertical.
2. If Ped is between 0 and 1 (i.e. the % change in demand from A to B is smaller than the percentage change in price), then demand is inelastic.
3. If Ped = 1 (i.e. the % change in demand is exactly the same as the % change in price), then demand is unit elastic. A 15% rise in price would lead to a 15% contraction in demand leaving total spending the same at each price level.
4. If Ped > 1, then demand responds more than proportionately to a change in price i.e. demand is elastic. For example if a 10% increase in the price of a good leads to a 30% drop in demand. The price elasticity of demand for this price change is –3

Inelastic demand (Ped <1)

Elastic demand (Ped >1)

Perfectly inelastic demand (Ped = zero)

Perfectly elastic demand

Unitary price elasticity of demand

Evaluation