Who this is for: Cambridge IGCSE Economics (0455) students who want price elasticity of supply (PES) — the formula, elastic vs inelastic supply, and why supply responds differently across industries — to become a reliable source of marks instead of a mirror of PED they copy without adapting.
What query it owns: how to understand and revise price elasticity of supply in Cambridge IGCSE Economics.
Why this is safe: this page owns the PES revision-guide angle, while Tutopiya’s Price Elasticity of Supply subtopic page owns the learning resource and the free Price Elasticity of Supply quiz owns the practice.

Price elasticity of supply (PES) measures how responsive quantity supplied is to a change in price. Cambridge IGCSE Economics (0455) expects you to calculate PES, classify supply as elastic or inelastic, and explain determinants such as spare capacity, time period and mobility of factors of production. This guide links each PES result to the explanation and calculation questions examiners set.

Key takeaways

• PES = % change in quantity supplied ÷ % change in price.
• Elastic supply (PES > 1): quantity supplied changes proportionally more than price.
• Inelastic supply (PES < 1): quantity supplied changes proportionally less than price.
• PES is usually positive (law of supply).
• Supply is more elastic when producers can increase output quickly (spare capacity, short production time).

What is price elasticity of supply in Cambridge IGCSE Economics?

Price elasticity of supply measures the responsiveness of quantity supplied to a change in the price of the good itself. Cambridge IGCSE Economics (0455) tests whether you can apply the percentage formula, interpret the result, and explain why supply of manufactured goods is often more elastic than supply of agricultural products or oil.

You can read the full explanation, worked examples and notes on Tutopiya’s Price Elasticity of Supply subtopic page before you attempt questions.

Core PES definitions you must know

Term	Definition	PES value
Price elastic supply	Qs responds more than proportionally to price change	PES > 1
Price inelastic supply	Qs responds less than proportionally to price change	PES < 1
Unit elastic supply	Qs responds proportionally to price change	PES = 1
Perfectly inelastic	Qs does not change when price changes	PES = 0
Perfectly elastic	Producers supply any quantity at one price	PES = ∞

How to calculate PES — step by step

1. Write the formula: PES = % ΔQs ÷ % ΔP.
2. Calculate % change in quantity supplied from the data given.
3. Calculate % change in price from the data given.
4. Divide to get PES (expect a positive value).
5. Classify: > 1 elastic, < 1 inelastic, = 1 unit elastic.
6. Explain using determinants — why is supply elastic or inelastic in this case?

Test yourself with the free Price Elasticity of Supply quiz once you can calculate and classify PES confidently.

Determinants of PES: what makes supply more elastic?

Determinant	More elastic (higher PES)	More inelastic (lower PES)
Spare capacity	Firms can increase output quickly	Operating at full capacity
Time period	Long run (time to expand)	Short run
Mobility of factors	Factors easily switched between uses	Factors specialised or fixed
Stocks/inventories	Goods can be drawn from stock	Perishable goods, no storage
Ease of entry	New firms can enter easily	Barriers to entry high

PED vs PES: quick comparison

Feature	PED	PES
Measures responsiveness of	Quantity demanded	Quantity supplied
Formula	% ΔQd ÷ % ΔP	% ΔQs ÷ % ΔP
Usual sign	Negative	Positive
Key determinants	Substitutes, necessity, income share	Spare capacity, time, factor mobility

PES in past-paper wording: command words that matter

Command word / phrase	What the question wants	Typical PES stem
Define	Precise meaning	”Define price elasticity of supply.”
Calculate	Apply the formula	”Calculate the price elasticity of supply.”
Explain	Cause and effect	”Explain why the supply of wheat is price inelastic in the short run.”
Distinguish between	Compare PED and PES	”Distinguish between price elasticity of demand and price elasticity of supply.”
Discuss	Consider implications	”Discuss the significance of price inelastic supply for consumers.”

Worked exam-style stems (how to answer the wording)

1. “Define price elasticity of supply.” Price elasticity of supply measures the responsiveness of quantity supplied to a change in the price of the good itself. Mark-scheme reward: responsiveness + quantity supplied + change in price.
2. “Price rises from $5 to $6. Quantity supplied rises from 200 to 260. Calculate PES.” % ΔQs = (260−200)/200 × 100 = +30%. % ΔP = (6−5)/5 × 100 = +20%. PES = 30/20 = 1.5 (elastic). Reward: correct method and classification.
3. “Explain why the supply of fresh fruit may be price inelastic.” Fruit is perishable so cannot be stored; production time is fixed by growing seasons; farmers cannot quickly increase output when price rises. Reward: perishability and/or time period linked to inelastic supply.

How PES connects to the rest of Cambridge IGCSE Economics

PES builds on Supply and pairs with Price Elasticity of Demand. The Cambridge IGCSE Economics resource hub links every Allocation of Resources subtopic.

Common mistakes students make

• Using the demand formula or applying PED rules to supply.
• Forgetting PES is usually positive (unlike PED).
• Confusing elastic supply with increase in supply (shift vs responsiveness).
• Ignoring the time period — supply is often more inelastic in the short run.
• Not explaining why supply is elastic or inelastic using determinants.

When you need more support

If PES calculations keep costing marks, work through the Price Elasticity of Supply quiz, then get focused help from a Cambridge IGCSE Economics tutor.

Frequently asked questions

Is PES hard in Cambridge IGCSE Economics? The formula mirrors PED but with quantity supplied. Focus on positive values and supply-side determinants.

What is the PES formula? PES = percentage change in quantity supplied ÷ percentage change in price.

When is supply price inelastic? When PES is less than 1 — quantity supplied changes by a smaller percentage than price, often in the short run or for perishable goods.

How do I revise price elasticity of supply effectively? Practise calculations, learn supply determinants, compare with PED, then take the Price Elasticity of Supply quiz.

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