How to Calculate Emissions from Travel

Calculating Scope 3.6 Emissions with Climatiq's Travel feature

Travel is a significant source of greenhouse gas emissions. Under the Greenhouse Gas Protocol (opens in a new tab), Business Travel is accounted for within category 6 of the Scope 3 and covers travel (by air, rail, road, sea, and hotel stays) undertaken by employees in vehicles, e.g. aircrafts, trains, and passenger cars that are not owned or operated by the reporting organization.

Choice of Method

As for all greenhouse gas calculations, the choice of methods depends on what data are available. The Greenhouse Gas Protocol provides a decision tree for selecting a method appropriate to the data you have at hand, reproduced below (Fig 1). According to the GHG Protocol methodology, the fuel-based method produces the most accurate results, followed by distance-based and then spend-based methods.

Fig. 1 Decision tree for selecting a calculation method based on available data

Fig. 1 Decision tree for selecting a calculation method based on available data

The relative magnitude and significance of emissions, the accuracy required for the purpose of emission calculations (e.g. internal decision-making or external reporting), and the level of effort required to get data should be considered when choosing the method. For example, rail travel is usually an insignificant part of total company emissions, and the spend-based approach, using readily available expenditure data, might be sufficient. However, for decision-making purposes (e.g. choosing to make a journey via rail or road), more accurate results are needed so using the fuel- or distance-based approach would be more appropriate.

Below are details for each calculation method:

  • Fuel-based Method: The amount of consumed energy (fuel or electricity) is used to estimate combustion and generation emissions. Standard fuel or electricity emission factors are applied. Note: emissions from assets owned or operated by the reporting company would normally fall under scope 1 and scope 2 emissions.

  • Distance-based Method: The distance traveled and mode of travel are used to estimate emissions. Distance-based emission factors are applied - either from standard datasets or calculated following Climatiq’s proprietary methodology.

  • Spend-based Method: The amount of money spent on the travel activity or hotel accommodation is used to estimate emissions. Emission factors are derived from Environmentally Extended Multi-Regional Input-Output Tables (EE MRIOT) such as EXIOBASE (refer to our guide on EE MRIOT (opens in a new tab) and to Stadler et al. 2021 (opens in a new tab)).

Climatiq’s Travel feature provides a complete toolkit tailored to your available data and desired accuracy level. The Travel feature can be used to estimate emissions from travel using distance or spend data. For estimations using the fuel-based method, refer to Climatiq’s Estimate endpoint and Energy feature (see also section Fuel-based method below).

The following sections detail how these methods are implemented using Climatiq's calculation endpoints.

A note on other travel emissions

Scope 3 emissions are those arising in the company’s value chain, specifically from using assets (vehicles) not owned or operated by the reporting organization. This means it does cover the use of “gray fleet”, i.e. employee-owned vehicles but it excludes emissions from company-owned or operated vehicles (scopes 1 or 2). Also employee commuting, using employee-owned vehicles is covered separately in Scope 3 category 7.

Climatiq’s Travel Feature: Methodology

This document outlines the methodology used by Climatiq’s API to calculate carbon emissions generated from various travel activities. Refer to the API Docs to learn more about how to use our Travel feature.

General considerations

All endpoints of the Travel feature accept either a QueryLocation, IataCodeLocation, UNLocodeLocation or CoordinateLocation as origin and destination to compute distance or location-specific emissions.

By default, calculations correspond to emissions for one passenger and for a one-way trip. In the case of a round trip, each leg of the journey should be calculated separately. The estimated CO2e applies to the primary mode of transportation and doesn’t account for the initial and final legs of the journey, such as transportation to and from the airport or railway station. Upstream and use-phase emissions for different modes of transportation and hotel stays are included in the results, except for the night-based method for hotel stays.

Upstream and use-phase emissions for different modes of transportation and hotel stays are included in the results, except for the night-based method for hotel stays.

Fuel-based method

When you have actual fuel use data, using this data will give the most accurate results. To calculate emissions from fuel data, you can choose between two options: use Climatiq’s Energy feature or Estimate endpoint. Climatiq’s Energy feature is a preferred choice, as it will also supply you with the automatic calculation of upstream emissions for a specific fuel type.

Distance-based method

Distance-based methods provide route-specific calculation of emissions originating from air, car, train, and taxi travels from origin to destination.

Air Travel

The air travel endpoint calculates emissions associated when flying based on emission factors from BEIS (opens in a new tab)1. The endpoint is designed to handle single-leg flights and categorizes them into short, medium, and long-haul flights for better accuracy. Cabin class is also taken into consideration with the option to specify whether the trip was in economy, business, or first class if known. For each flight, the following criteria are used to determine the selection of emission factor:

  • Flight Distance: The distance between the specified origin and destination is calculated by the API, using the Great Circle Distance method (Haversine formula). This determines the appropriate “haul” for choosing the emission factor: domestic, short, or long, where:
    • domestic flight is within UK or < 483km
    • short-haul flight is > 483km < 3700km
    • long-haul flight is > 3700km
  • Cabin Class: Optional. This can be specified as economy, business, or first. If no cabin class is specified, the default “average” is used. The only class available for domestic flights is “average”.
  • Year. Optional. The endpoint chooses the emission factor for the closest year.

The resulting carbon footprint automatically includes the Radiative Forcing factor, which is used to account for impacts of fuel burn in high altitudes. The multiplier in the BEIS emission factors is currently 1.9, so estimated emissions are approximately 1.9 times higher with the RF multiplier than without.

Upstream emissions for travel

The associated emissions factors from BEIS are used to calculate well-to tank (WTT) emissions associated with the production, transport, and distribution of fuel.

Car Travel

The car travel endpoint allows users to calculate route-specific emissions generated when driving between two points. The endpoint accommodates a range of car types, classified as follows:

By powertrain / car type:

  • Diesel
  • Petrol
  • Hybrid
  • BEV (Battery Electric Vehicle)
  • PHEV (Plug-in Hybrid Electric Vehicle)

By engine / carsize (see car examples here):

  • Small
  • Medium
  • Large
  • Average - if car size is not provided, the API will default to average engine size for calculations.

For cars with unspecified (unknown) fuel types, the average factor from UK BEIS will be used globally, except in the USA where the EPA provides a specific average car factor.

For petrol and diesel cars, the endpoint will default to UK BEIS emission factors for both the UK and regions outside of the UK. Emissions associated with burning a liter of petrol or diesel vary little by region (depending on driving style, road quality etc.) so the same emission factor can be used worldwide. However, for electric cars (BEV / PHEV), emissions vary based on the carbon intensity of the grid, so region-specific factors are used.

The following steps are taken to estimate emissions from BEV and PHEV cars in different regions:

Battery Electric Vehicle (BEV):
  • Total distance (based on origin and destination) is calculated.
  • Amount of kWh needed to travel this distance is calculated, based on the electricity consumption rate (kWh / km) for the specific size of BEV. These consumption rates are derived from the UK BEIS data.
  • The amount of kWh is sent to Climatiq’s Energy endpoint, which returns the amount of CO2e based on the grid intensity of the location-based grid mix.

Plug-in Hybrid Electric Vehicle (PHEV):
  • Total distance (based on origin and destination) is calculated.
  • Amount of kWh needed to travel this distance is calculated, based on the electricity consumption rate for the specific size of PHEV. These consumption rates are derived from the UK BEIS methodology.
  • Amount of petrol in liters needed to travel this distance is calculated based on the petrol consumption rate for the specific size of PHEV (derived from the BEIS data).
  • The amount of kWh and liters of petrol are sent to Climatiq’s Energy endpoint, which returns the amount of CO2e based on the regional electricity emission factors and the petrol emission factor.
Upstream emissions for travel

The endpoint returns the upstream (Well-to-tank) emissions from the production, transport, and distribution of fuel, and any electricity transmission/distribution (T&D) losses.

For cars with Internal Combustion Engines, UK BEIS WTT (Well-to-tank) factors are used for all countries except for the US.The EPA doesn’t provide WTT factors for the US, so they’re estimated as a percentage ratio from the fuel combustion emission factor, using BEIS data for an average car:

% = EFWTTEF_{WTT} / EFfuel  combustionEF_{fuel\;combustion}

For BEV and PHEV cars: emissions from electricity generation, along with WTT for electricity generation, transmission and distribution losses and WTT for transmission and distribution, as well as WTT for fuels for PHEV cars are calculated by Climatiq’s Energy endpoint.

Train Travel

The train travel endpoint calculates emissions for rail journeys between specific origins and destinations.

The distance between the origin and destination is calculated according to a routing algorithm through rail networks. We do not have full coverage of the global rail network. If data on specific rail segments is missing, we might use car routes for distance calculations instead of rail routes.

The selection of emissions factors for calculating emissions from train travel depends on the availability of suitable factors from the official governmental source for a given country. For the UK and the USA, the emission factors provided by the country’s official sources are used, i.e. BEIS and EPA respectively.

For countries where no rail emission factors are available, emissions will be calculated as a weighted average between electric and diesel train travel, based on the country's rail electrification rate.

Rail electrification rates

These sources provide the average electrification rates used in our methodology for different countries inside and outside of the EU: EUROSTAT 2021 (opens in a new tab), EUROSTAT 2021 (opens in a new tab), European Commission 2021 (opens in a new tab).

Average energy consumption for diesel and electric trains

Diesel or electricity (energy) consumption per passenger kilometer is based on average occupancy and average energy consumption per train at an EU level. The energy intensities are sent to Climatiq's Energy feature to estimate emissions from diesel and electric train travel. The results are weighted by the amount of travel done in each type of train to get a final emissions per passenger kilometer factor.

Emission factors for rail journeys

For the UK and US, the endpoint will default to official train travel emission factors from the governmental sources: BEIS and EPA, respectively.

For other countries, the fuel emission factor for diesel, as well as for electricity in a specific location will be determined through Climatiq’s Energy endpoint.

For international rail travel, the endpoint uses the origin country for emission calculations. If the origin is in the UK or the USA, specific emission factors for these countries will be selected. For other countries, the endpoint will select the electrification rate of the origin and forward the data to Climatiq’s Energy endpoint. If emission factors for the origin country are unavailable, the destination country's electrification rates will be used. If electrification rates aren’t available for either the origin or destination, diesel train travel will be the default. This is on the assumption that diesel train travel is more prevalent in countries where no data exists.

Upstream emissions

WTT emissions for diesel and electricity, electricity generation, and T&D (transmission and distribution) are calculated by the Energy endpoint when travel-specific factors aren’t provided by official emission factor sources.

BEIS provides emission factors for WTT separately which we use for upstream emissions calculation. The EPA provides only use_phase emission factors. In this case, WTT emissions are estimated as a percentage ratio from the use_phase emission factor, using BEIS emission factor for an average train:

% = EFWTTEF_{WTT} / EFuse  phaseEF_{use\;phase}

Taxi Journeys

To calculate emissions from taxi trips, use the Car endpoints: spend-based method or distance-based method.

Spend-based method

The API utilizes spend-based emissions factors from EXIOBASE (opens in a new tab) to calculate the carbon footprint of travel by train, car, or air for your selected location. Note that the EXIOBASE spend-based emission factor, used for the road travel is, in fact, an average emission factor for a mix of different types of transport: urban and suburban passenger land transport, taxi operation, other passenger land transport and freight transport by road and can therefore produce results of lower accuracy. Climatiq advises to use fuel-based or distance-based method, where possible. Learn more about the science behind spend-based emission calculations here (opens in a new tab).


Hotel nights are accounted for using both the activity-based method — determined by the number of nights spent in a hotel in a given region — or the spend-based method, which is based on the amount spent on a hotel stay in that region.

For the night-based method, the API applies an emission factor from the BEIS dataset corresponding to the region of your stay. The BEIS dataset covers up to 54 different regions, depending on the data release year.

For the spend-based method, the API applies EXIOBASE emission factors for hotel stays, corresponding to the region of interest. The API will also automatically apply inflation correction and currency conversions as required for spend-based calculations. Read more about the importance of inflation correction in this guide.

In cases when the region of interest is not covered by BEIS or EXIOBASE, a fallback logic is applied. For the night-based method, the fall-back logic is as follows:

Specified city → Specified country → median of the same continent of the region

For the spend-based method, the following fallback logic is applied:

Specified country → Rest-of-the-World sub-region from EXIOBASE

Upstream emissions for hotel accommodation

Upstream emissions for hotel stays are accounted for only with the spend-based method, as it is a part of the emissions factor from EXIOBASE by default (read why in this article (opens in a new tab)). BEIS emissions factors do not account for the upstream emissions related to hotel use.

1 The rationale behind using the BEIS emission factors: while these factors are based on the UK’s plane mix and occupancy rates, they offer cabin class options not found in other datasets, and cabin class significantly impacts emissions. EPA uses BEIS emission factors in their dataset for US domestic and international flights.