Price Elasticity of Demand
How sharply the quantity customers buy responds to a change in price - and what that means for whether a price move helps or hurts revenue.
What it is
Price elasticity of demand measures how sensitive customer demand is to a change in price. It answers: if I change price by some percentage, by what percentage does quantity sold move? Demand is called elastic when quantity reacts strongly (a small price rise loses a lot of volume) and inelastic when quantity barely moves (customers keep buying even as price rises). It captures a simple business truth - some products people will abandon the moment they get pricier, and others they will buy almost regardless. Knowing which case you are in is what tells you whether raising price is a gift or a mistake.
When to use it
Use it in any pricing case where you are considering a price change and need to predict what happens to volume and revenue. It is the bridge between 'we could raise price 10%' and 'but we would lose 25% of customers'. It is central to reasoning about discounts, premium positioning, and competitive price wars. It matters less when volume is capacity-constrained (you cannot sell more anyway) or when the decision is qualitative. Do not assume an elasticity number you have not grounded in the product's substitutes and necessity - it is an empirical quantity, not a default.
How to apply it
The formula is: Elasticity = (% change in quantity demanded) / (% change in price). Both are percentages, so elasticity is a unitless ratio; it is conventionally negative (price up, quantity down) and people usually discuss its magnitude. If the magnitude is greater than 1, demand is elastic - quantity moves more than price in percentage terms. If it is less than 1, demand is inelastic. The intuition that matters: when demand is inelastic (magnitude < 1), raising price increases revenue because you lose proportionally less volume than you gain in price; when demand is elastic (magnitude > 1), raising price reduces revenue. So the practical question is not 'what is the exact elasticity?' but 'is this product more or less than unit-elastic?' - because that flips the direction of the right move. Drivers of elasticity to reason from: availability of substitutes, whether the item is a necessity, and how large it looms in the buyer's budget.
Common mistakes
The biggest error is ignoring elasticity entirely - assuming a price rise flows straight to revenue with volume unchanged, which is only true if demand is perfectly inelastic. Another is mixing up the direction: forgetting that raising price on an elastic product can cut revenue. People also apply one elasticity to a whole market when segments differ enormously (loyal customers inelastic, marginal ones elastic). And they confuse elastic demand with 'price is high' - elasticity is about the responsiveness of quantity to a change, not the level of price.
Example
A city transit authority is deciding whether to raise fares 20% to close a budget gap. The naive view: 20% more revenue. Applying elasticity: commuters have few alternatives for the daily trip, so demand is fairly inelastic - suppose a 20% fare rise costs only about 8% of ridership (elasticity magnitude roughly 0.4). Revenue rises, because the percentage volume loss is smaller than the percentage price gain. But weekend leisure riders, who can simply stay home or drive, are far more elastic; the same fare rise could wipe out much of that ridership. The single answer 'raise fares' hides two different elasticities, and the smart move may be to raise commuter fares while protecting discretionary trips.
Practice it
Practice on pricing cases by always asking, before you move a price, whether demand for this specific product and segment is elastic or inelastic, and reasoning from substitutes and necessity to justify your call. The skill to build is connecting the elasticity magnitude to the direction of the revenue effect, and refusing to treat a price change as pure margin.