2 Price Elasticity of Supply

Meaning and interpretation

Price elasticity of supply measures how responsive the quantity sellers offer is to a change in a good’s price, assuming other conditions remain unchanged. It is the percentage change in quantity supplied divided by the percentage change in price:

Supply elasticity is usually positive: when a good’s price rises, sellers generally have an incentive to offer more. The measure has no units because it is a ratio of percentages.

The size of the elasticity describes how strongly quantity supplied changes relative to price:

• When $E_s > 1$, supply is elastic: quantity supplied changes by a larger percentage than price.

• When $E_s = 1$, supply is unit elastic: quantity supplied and price change by the same percentage.

• When $0 < E_s < 1$, supply is inelastic: quantity supplied changes by a smaller percentage than price.

• When $E_s = 0$, supply is perfectly inelastic: quantity supplied does not respond to price.

Calculating elasticity

For two price-and-quantity observations, the midpoint method calculates each percentage change using the average of its starting and ending values. This makes the elasticity calculation consistent whichever direction the comparison is made.

For example, suppose a seller increases quantity supplied from $100$ to $130$ units when price rises from $\$10$ to $\$12$. The percentage change in quantity is $\frac{30}{115}\times 100 \approx 26.1\%$, and the percentage change in price is $\frac{2}{11}\times 100 \approx 18.2\%$. The supply elasticity is $\frac{26.1}{18.2} \approx 1.44$, so supply is elastic over this interval.

This estimate means that, over the measured range, a $1\%$ price rise is associated with about a $1.44\%$ increase in quantity supplied. It describes responsiveness between these observations; it does not promise that every price change will produce exactly that response.

What affects seller responsiveness

Supply is generally more elastic when sellers have more time to respond. In the short run, firms may be limited by current equipment, staffing, growing cycles, or construction schedules. Given longer, they may hire and train workers, change production methods, build facilities, or new firms may enter the market.

For example, apartment supply may respond little to higher rents in a few months, but more substantially over several years as buildings are constructed or converted.

A firm with unused capacity—such as machines, workers, storage, or floor space—can often increase output quickly when prices rise. A firm already operating near its capacity may be unable to expand much without costly investment, making its supply less elastic in the short run.

The availability of inputs also matters. When labor, materials, land, equipment, or other inputs are readily available, sellers can more easily increase output. Scarce inputs, shortages, specialized skills, or long delivery times constrain the response. The ability to substitute other inputs or redirect resources from alternative products can make supply more responsive.

These conditions can differ across industries and time periods. A product with limited supply today may have a more elastic supply after firms have time to expand capacity or secure inputs.

• Unit elastic supply

• Inelastic supply

• Perfectly inelastic supply