Elasticity = (Demand Change %) / (Price Change %)
Price Change % = ((Final Price - Initial Price) / Initial Price) × 100
Demand Change % = ((Final Demand - Initial Demand) / Initial Demand) × 100
Initial Income = Initial Price × Initial Demand
Final Income = Final Price × Final Demand
Income Change % = ((Final Income - Initial Income) / Initial Income) × 100
Example:
Initial Price: $ 100, Final Price: $ 120
Initial Demand: 1000, Final Demand: 800
Price Change % = ((120 - 100) / 100) × 100 = 20 %
Demand Change % = ((800 - 1000) / 1000) × 100 = -20 %
Elasticity = |-20 / 20| = 1.0 (Unit Elastic)