All courses › Technology, Ethics and Sustainability › Functional unit

Functional unit

To compare two products fairly, emissions must be calculated per benefit, not per product. The functional unit describes the benefit, for example one kilometre of transport or one year of use. A product that lasts twice as long spreads its emissions over more units.

e = \frac{E_{tot}}{N}

emissions per functional unit

Symbols

$e$	emissions per unit	kg CO_2e
$E_{tot}$	total life cycle emissions	kg CO_2e
$N$	number of functional units delivered

Example

Bike A: 150 kg CO₂e over 15,000 km. Bike B: 100 kg CO₂e over 5000 km.

A gives 10 g/km and B 20 g/km, so A is better even though its total is higher.

Choose the functional unit before calculating. It often decides which product wins.

Practise life cycle and carbon accounting for free →

← Whistleblowing and conflict of interest · CO₂ equivalents →

Part of Technology, Ethics and Sustainability: Life cycle and carbon accounting.