Price Elasticity of Supply (PES)

$\text{PES} = \dfrac{\%\,\Delta\,Q_s}{\%\,\Delta\,P}$

PES is the percentage change in quantity supplied divided by the percentage change in price. Both numbers are percentages, not raw unit changes. The percentage-change formula is the same as for PED:

$\% \,\text{change} = \dfrac{\text{new value} - \text{old value}}{\text{old value}} \times 100$

PES is positive: the supply curve slopes upward, so a price rise produces a rise in quantity supplied. Both percentage changes have the same sign, so the ratio is positive. There is no sign-convention trap here, unlike PED.