My staff share cars on business trips: do I count person-km or vehicle-km?

Count the unit your factor uses. For a factor per vehicle-kilometre, divide the staff travelling by the number in each car, then multiply by distance and factor. The Greenhouse Gas Protocol's example: 100 staff, 3 to a car, 100 km, 4 kg a vehicle-km is 100 / 3 x 100 x 4 = 13,333 kg.

Match the unit to the factor

A car factor is usually per vehicle-kilometre: the car burns the same fuel whether it holds one person or three. A bus or train factor is usually per passenger-kilometre. Using person-kilometres with a per vehicle factor counts a shared car once per rider.

The guide's example

• 10 staff, 2 to a car, 50 km at 1 kg a vehicle-km: 10 / 2 x 50 x 1 = 250 kg.
• 20 staff, 2 to a car, 200 km at 2 kg: 20 / 2 x 200 x 2 = 4,000 kg.
• 100 staff, 3 to a car, 100 km at 4 kg: 100 / 3 x 100 x 4 = 13,333 kg.
• Road total 17,583 kg of carbon dioxide equivalent (CO2e). The factors in the guide are examples to show the arithmetic.

Which category

Cars you own or control are Scope 1. Rented cars and employees' own cars on business trips are Scope 3 Category 6. See business car travel: which scope for the rest.

Nine engineers, three cars, 300 km round trip (estimate)

• Car factor: 2.176 kg carbon dioxide (CO2) a litre of petrol / 15 km a litre = 0.145 kg a vehicle-km
• Right: 9 / 3 x 300 x 0.145 = 131 kg
• Wrong: 9 x 300 x 0.145 = 392 kg, three times too high

The 15 km a litre is an example fuel economy; the petrol factor is the Intergovernmental Panel on Climate Change carbon content at Indian density, an estimate.

What Senseible does here

Senseible reads fuel invoices, so petrol or diesel bought for company cars (Scope 1) is on record in litres. Trips in hired or personal cars are counted from the trip log you keep.

• Business car travel: which scope
• Employee commuting emissions survey
• Business travel sample: 400 of 4,000 staff

Sources: GHG Protocol, Technical Guidance for Calculating Scope 3 Emissions, Category 6, GHG Protocol, Corporate Value Chain (Scope 3) Standard

Last reviewed 2026-11-04. The guidance is dated 2013; its example factors are not real factors.