Sustainable business travel, measured

Estimates, not a certified footprint. Emission factors are averages. The figures on this page are official factors quoted from the UK and US government sources listed at the end, with the date we checked them; worked examples are arithmetic on those factors. Have your reporting method reviewed by whoever signs off your sustainability or annual report.

What counts as business travel emissions

In the GHG Protocol's guidance on scope 3 emissions, business travel is scope 3, category 6: emissions from employees traveling for work in vehicles the company doesn't own or operate, such as aircraft, trains, buses and rental or personal cars. Companies may optionally include hotel stays. Your scope 3 figure for business travel includes the transport companies' own direct emissions, such as an airline's.^[1]

For most companies of 100 to 1,000 people, that means three things to measure: flights, rail and hotel nights, with ground transport as a smaller, harder-to-capture fourth. In the UK factors below, flights have the highest factors per passenger-kilometer, and in the US factors short-haul flights are the highest per passenger-mile, which is why the choices in this guide are mostly about which trips are taken, by which mode, and in which cabin.

Measure it from your bookings

The GHG Protocol describes three ways to calculate business travel emissions: from the fuel used, which travelers can't know; from distance and mode, multiplied by an emission factor for each mode; or from money spent, multiplied by spend-based factors.^[1] The distance-based method is the practical choice when trips are booked through a program, because the bookings already hold what it needs:

• Flights: the airports of each leg and the cabin. Distance comes from the airports, so a connection counts as two legs.
• Rail: origin and destination stations, or the distance, and whether the journey is national or international.
• Hotels: the number of room nights, and the country.
• Who and why: the traveler's department and project, so the totals can be reported where decisions are made.

The spend-based method is a fallback for travel you can't see in detail, such as expensed taxis or trips booked outside the program. Its factors are much coarser, so report the two separately, and treat moving trips into the program as part of improving the data.

To try the distance-based method on your own regular routes, the flight emissions estimator gives CO2e per trip and per year, and its method section shows each step.

Choose a factor set, and keep it

Two free, official factor sets cover business travel. Pick one, state it, and keep it.

UK DESNZ conversion factors

The UK Department for Energy Security and Net Zero publishes a new set each year, with a methodology report and a report on major changes.^[2] The 2026 set was first published on Jun 11, 2026.^[3] It gives factors per passenger-kilometer for flights by haul and cabin, with and without radiative forcing (the extra warming effect of emissions at altitude), and for rail, coach and hotel stays by country. DESNZ describes the factors as suitable for UK-based organizations and for international organizations reporting on their UK operations, and says other uses are at the user's own risk.^[2] If you use them for anything else, such as a US company's whole program, say so in your method.

US EPA Emission Factors Hub

The US Environmental Protection Agency's Emission Factors Hub gives default factors for organizational reporting; its 2025 update, from January 2025, includes business travel.^[7] Its business travel factors are per passenger-mile and cover combustion only, without upstream emissions. For air travel, EPA uses DEFRA's 2022 figures, held constant because the 2023 and 2024 UK releases reflected the reduced load factors of COVID-19.^[8]

Factors change every year

The change can be larger than anything your travel program did. DESNZ's 2025 update cut its business air factors by 16% to 42% against 2024: the earlier figures came from COVID-affected 2021 data with unusually low load factors, and as planes filled up again, emissions per passenger-kilometer fell.^[5] The 2026 update made no major changes to air, but lowered national rail by 13% and raised international rail by 154% to 156%.^[4]

Our emissions estimator and the silentVIP portal use the 2024 set today, so their flight figures are higher than the 2026 factors would give for the same trips. Whichever set you use, record its year with each report, and when you move to a new set, restate the previous year with it, or flag the change, so a factor update isn't read as a reduction.

Rail against air

Rail is the clearest lever for short trips, and the factors show why. They also show that the gap depends on where you are.

In the UK factors

Per 100 passenger-kilometers, a domestic flight comes to 22.9 kg CO2e on the 2026 factor, including radiative forcing, against 3.1 kg by national rail.^[3] Even without radiative forcing, the domestic flight factor is 4.4 times the national rail one.

In the US factors

Over 200 passenger-miles, a short-haul flight comes to 41.4 kg CO2 on EPA's factor, against 4.6 kg on Amtrak's Northeast Corridor.^[8] On Amtrak's other routes the same distance comes to 29.8 kg, closer to the flight, and EPA's factor for those routes is above its medium-haul air factor per passenger-mile.^[8] A train and a plane don't cover exactly the same distance between two cities, so treat these as comparisons of factors, not of journeys.

What this means for a policy

A rail-first rule fits where trains are frequent and the trip takes a comparable time door to door: for example London to Paris, or the Northeast Corridor, which EPA's factors describe as running from Boston to Washington, D.C.^[8] Write the rule by route or by journey time, not as a blanket preference, so it applies where it makes a real difference and travelers can see why.

Hotel nights

Hotel nights are counted per night rather than per kilometer, they're easy to measure, and they add up on long stays. DESNZ publishes a factor per room per night for each country it covers.^[3]

The lever here is mostly the number of nights: trips that combine meetings, or avoid an extra night on the road, reduce both cost and emissions. The country factor isn't something a traveler can choose, so it belongs in the measurement, not the policy.

Policy levers

The levers below are choices for your own policy. None of them is a rule anyone has to follow, and the right mix depends on why your people travel.

1. Ask what the trip is for. A trip purpose on every request makes it easier to see which trips could be combined, shortened or held by video, without banning any of them.
2. Rail first, where it fits. A rule for named routes or journey times, as above. Make rail as easy to book as a flight, through the same program.
3. Cabin rules. On the DESNZ 2026 long-haul factors, the factor for a business-class seat is 2.9 times the economy factor per passenger-kilometer, and first class 4.0 times.^[3] A rule that allows business class only above a set flight time is a cost and an emissions decision at once.
4. Fewer legs. A connection adds distance compared with a nonstop flight on the same trip. Where the fare difference is small, a nonstop is usually the better choice on both counts.
5. Fewer nights. Plan multi-meeting trips so they don't add a night, and let travelers come home the same day when the schedule allows it.
6. A number per department. Report emissions next to spend, by department, so the people who decide on trips see both. A target, if you set one, should use the same factor set from year to year.

Our travel policy guide covers how rules like these are written and enforced, and the policy builder turns them into a sample policy.

Report it

A short, consistent report does more than a detailed one that changes every quarter. For each period, show:

• Emissions by mode (flights, rail, hotel nights), by department, and the total, next to spend.
• The factor set and year, whether flights include radiative forcing, and what's left out, such as taxis or trips booked elsewhere.
• The same period last year, on the same factor set.
• One or two changes worth acting on: a route that could be rail, a department whose cabin mix changed.

Where silentVIP fits

Every flight booking in the silentVIP portal gets a CO2e estimate from its route, using the DESNZ 2024 factors with radiative forcing; hotel nights use a per-room-night factor and rail a per-passenger-kilometer factor. The estimates cover flights booked through silentVIP with a route, hotel nights and rail. Car rentals, taxis and travel booked elsewhere are not included. Totals by department, project and traveler appear in reports and export as CSV.

Rail is booked through the same program as flights: intercity rail including Amtrak, Eurostar and major European operators. The sustainability section of our program overview has the details.

Questions

Sources

Emission factors and other outside statements on this page come from these public sources, each checked on Oct 22, 2026. Worked examples are arithmetic on the factors shown. silentVIP's own method comes from our program overview and the estimator's method.

1. GHG Protocol, Technical Guidance for Calculating Scope 3 Emissions, Category 6: Business Travel. Category 6 covers emissions from transporting employees for business in vehicles owned or operated by third parties, such as aircraft, trains, buses and passenger cars; companies may optionally include hotel stays. It sets out three methods: fuel-based, distance-based (distance and mode times an emission factor for the mode) and spend-based (money spent times secondary, EEIO, factors). https://ghgprotocol.org/sites/default/files/2022-12/Chapter6.pdf (checked Oct 22, 2026)
2. UK government, Government conversion factors for company reporting of greenhouse gas emissions (GOV.UK). The collection of yearly factor sets. An update is published each year, with a methodology report and a major changes report. The factors are described as suitable for UK-based organizations of all sizes and international organizations reporting on their UK operations; they may also be used for other purposes, but users do so at their own risk. https://www.gov.uk/government/collections/government-conversion-factors-for-company-reporting (checked Oct 22, 2026)
3. DESNZ, Greenhouse gas reporting: conversion factors 2026 (GOV.UK). First published Jun 11, 2026; the flat file was revised on Jul 31, 2026 to correct some values first reported as 0. Figures on this page are from the revised flat file: business travel by air (to/from UK, with and without radiative forcing), national and international rail, coach, and hotel stays per room per night. https://www.gov.uk/government/publications/greenhouse-gas-reporting-conversion-factors-2026 (checked Oct 22, 2026)
4. DESNZ, 2026 conversion factors: major changes report. Business travel by air: no major changes from 2025. National rail: -13%, which DESNZ attributes to significant changes to passenger.km and fleet composition since the estimates were last updated in 2021, from pre-pandemic figures. International rail: 154% to 156%, due to large changes in service patterns and rolling stock utilization compared with the previous, pre-pandemic factors. https://assets.publishing.service.gov.uk/media/6a2940653b15d05a7ce3202f/2026-GHG-conversion-factors-major-changes-report.pdf (checked Oct 22, 2026)
5. DESNZ, 2025 conversion factors: major changes document. Business travel by air: all factors -16% to -42% against the 2024 update. The figures were last updated in the 2023 publication, using COVID-affected 2021 data with unusually low load factors; load factors have gone back up, so emissions per passenger.km fell. https://assets.publishing.service.gov.uk/media/6846b6d04d039a010411f0c9/2025-GHG-CF-major-changes-document.pdf (checked Oct 22, 2026)
6. DESNZ, Greenhouse gas reporting: conversion factors 2024 (GOV.UK). First published Jul 8, 2024, updated Oct 30, 2024 for a small rounding error. This is the set the silentVIP emissions estimator and portal use; the 2024 values on this page were checked against its flat file (v1.1). The estimator's long-haul business factor (0.58029) and premium economy factor (0.32016) are one step in the last decimal place above v1.1's 0.58028 and 0.32015. https://www.gov.uk/government/publications/greenhouse-gas-reporting-conversion-factors-2024 (checked Oct 22, 2026)
7. US EPA, GHG Emission Factors Hub. Default emission factors for organizational greenhouse gas reporting. The 2025 update (January 2025) includes updated factors for business travel. Page last updated Jan 12, 2026. https://www.epa.gov/climateleadership/ghg-emission-factors-hub (checked Oct 22, 2026)
8. US EPA, GHG Emission Factors Hub 2025 (spreadsheet), Table 10. Table 10, Scope 3 Category 6 (business travel) and Category 7, for the distance-based method, in kg CO2 per passenger-mile: air short haul (under 300 miles) 0.207, medium haul (300 to 2,300 miles) 0.129, long haul (2,300 miles or more) 0.163; Amtrak intercity rail, Northeast Corridor (Boston to Washington, D.C.) 0.023, other routes 0.149, national average 0.096; bus 0.066. The factors are combustion emissions only (tank-to-wheel), with methane and nitrous oxide listed separately in grams. The air factors are DEFRA's 2022 figures, held constant because the 2023 and 2024 releases reflected reduced COVID-19 load factors. https://www.epa.gov/system/files/other-files/2025-01/ghg-emission-factors-hub-2025.xlsx (checked Oct 22, 2026)

Last reviewed: Oct 22, 2026. Spotted something out of date? Email support@silentvip.com.

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