Fleet & Mobile Combustion Emissions Calculators

Pick your starting point

Know what data you have? Go straight to the calculator. Unsure whether to work from fuel or from mileage, or whether a vehicle even belongs in your Scope 1? The decision table and what each calculator covers resolve it.

Which fleet calculator do I need?

One question settles it, and it is not about your vehicles. It is about your data: do you have litres, or do you have miles? Everything else follows.

What each calculator covers

Two of these measure the same emission by different routes; the third answers a question before the emission exists. Which route you can take is decided by your data, not your preference.

Fuel-based versus distance-based — the only methodological choice here

Every fleet figure comes from one of two routes. The fuel-based route takes litres purchased and multiplies by a per-litre factor: it is a direct measurement of the carbon you actually bought, and it captures everything — idling, a badly tuned engine, a heavy right foot, cold-weather economy loss. The distance-based route takes kilometres and multiplies by a per-km factor for that vehicle class: it is an average of how that vehicle type performs across the national fleet, which your vehicles may or may not resemble. Where you have fuel data, use it. The distance route exists because mileage logs are often all that survives — not because it is equivalent.

Fleet carbon footprint calculator — the distance route, done properly

The fleet carbon footprint calculator works from a vehicle list and annual mileage, applying DEFRA per-km factors by class and fuel. Car size drives it — an average diesel car runs 0.17265 kg CO₂e/km against 0.19794 for a diesel 4×4, on DEFRA 2026 factors — and commercial vehicles diverge much further: an average-laden articulated HGV is 0.93374 kg CO₂e/km, more than five times the car. It is the right tool when you know what you run and how far, which is the position most fleets are in at first count. See the fleet emissions methodology.

Mobile combustion calculator — the fuel route, and everything that isn’t a car

The mobile combustion calculator works at the fuel level: litres in, kg CO₂e out. Pump diesel is 2.58354 kg CO₂e/litre and petrol 2.075 on DEFRA 2026 — note that the biofuel-blended forecourt fuels sit *below* their pure mineral equivalents (2.66155 and 2.35372 respectively), because the biogenic fraction is accounted separately. It also covers what the fleet calculator cannot: red diesel in site plant at 2.75541 kg CO₂e/litre, marine gas oil in a workboat at 2.77139, LPG forklifts at 1.55713, gensets, agricultural machinery. If it burns fuel and you own it, it belongs here — “fleet” in the GHG Protocol sense means every mobile asset, not just the ones with number plates.

EV vs petrol — the argument that turns on two assumptions

The EV vs petrol lifecycle calculator compares powertrains across manufacturing and use, and the honest framing is that an EV starts in deficit: battery production front-loads emissions a combustion car does not carry. It repays that deficit over distance, and how fast depends on exactly two things — the grid it charges on and the kilometres it covers. Both are explicit inputs rather than buried assumptions, because both decide the answer. The UK case has moved sharply: charging an average battery-electric car in the UK is 0.02686 kg CO₂e/km against 0.17265 for an average diesel — but that gap widened materially when the UK grid factor fell from 0.177 to 0.131 kg CO₂e/kWh in the DEFRA 2026 refresh, a 26% drop. Run this before a procurement decision, not after. See the EV vs petrol lifecycle methodology.

Well-to-tank — the half of your fuel that isn’t in Scope 1

A per-litre combustion factor covers the carbon that leaves your exhaust. It does not cover extracting, refining and delivering that litre to the pump — that is well-to-tank, and it lands in Scope 3 Category 3, not Scope 1. For an HGV, the upstream share is far from trivial: 0.21898 kg CO₂e/km of WTT sits alongside 0.93374 of tailpipe, roughly a fifth again on top. It is a separate calculation on the same litres, and the well-to-tank calculator handles it. Omitting it is defensible if you say so; omitting it silently is not.

How the numbers are built

Every factor on this page comes from DEFRA 2026, held and versioned in the MasterBrain data layer, and the full set is documented in the DEFRA emission factors reference. Accounting follows the GHG Protocol Corporate Standard; a UK fleet’s Scope 1 figure feeds directly into SECR disclosure and into an ISO 14064-1 inventory. Whether a vehicle is in your Scope 1 at all is an operational control question — a leased vehicle you direct the use of is generally yours; one you merely finance may not be.

The fuel you put in decides most of the answer:

What a fleet estimate gives you is unusually solid by Scope 3 standards — because it is not Scope 3. If you work from fuel receipts, you are measuring a purchase you can audit, not surveying a behaviour you can only approximate. The weakness sits in the distance route: a per-km class average assumes your vehicles perform like the national fleet, which a fleet of old vans or a duty cycle of short urban trips will not. The other soft edge is boundary rather than factor — grey fleet mileage, employee-owned cars driven on company business, is not Scope 1 at all and belongs in Category 6. If your fleet number looks suspiciously large, that misplacement is the first thing to check.

Not your vehicles? Zoom out

Ownership is the whole test here. A vehicle you own or control is Scope 1 — you buy the fuel, you burn it, it is yours. Pay someone else to move the same load and it becomes Scope 3: goods carried by a third-party carrier are Category 4 or 9, covered by the freight emissions calculators in tonne-kilometres rather than litres. People travelling on your instruction in vehicles you don’t own — flights, taxis, hire cars, an employee’s own car on a work trip — are Category 6, covered by the business travel and commuting calculators. That last one catches people out: a hire car for a client visit is business travel, not fleet, even though someone drove it on your business. All three slices sit under the transport & logistics emissions calculators hub.

From a fleet number to a reduction plan

A fleet figure is one of the few Scope 1 lines with an obvious lever attached. Once you know the split by vehicle class and fuel, the sequence is usually the same: right-size the fleet, then shift the duty cycles that suit electrification, then address what’s left. Run the lifecycle comparison before committing — the payback depends on your grid and your annual mileage, and a low-mileage EV on a dirty grid is a slower win than the headline suggests. Remember that electrification moves the emission to Scope 2 rather than deleting it, so track the pair. When the fleet lines are solid they fold into the wider inventory: the Scope 1-2-3 inventory aggregator and the ISO 14064-1 inventory calculator roll them up, and UK reporters can carry the same figure into the SECR calculator.