HGV Fuel Log: Tracking Diesel and MPG per Vehicle

When diesel was 140p a litre, a truck that quietly lost half a mile per gallon was an annoyance. With the UK average pump price at 198.58p in the week of 2 November 2026, according to the government's weekly road fuel prices, the same truck is costing you real money every week, and most small fleets only find out when the fuel card statement arrives.

A proper HGV fuel log fixes that. This guide covers what to record at every fill, how to work out MPG per vehicle without fooling yourself, which outliers deserve a phone call, and how to talk to drivers about idling and driving style without starting a row in the yard.

What should an HGV fuel log record at every fill?

A fuel log is only as good as its worst entry. Each fill needs enough detail to stand on its own if someone queries it six months later:

• Date and time of the fill
• Vehicle registration and, for artics, the trailer number coupled at the time
• Driver name
• Odometer reading at the pump (not from memory at the end of the shift)
• Litres dispensed
• Price per litre and total cost
• Where: fuel site, bunker at the yard or roadside forecourt
• Whether the tank was filled to the top (yes or no)
• A photo of the receipt or pump display
• AdBlue as a separate line, never mixed into the diesel litres

The "filled to the top" flag is the one most logs miss, and it is the one that makes MPG figures trustworthy.

Keep the receipts too. HMRC's VAT notice on motoring expenses explains, at section 9.10, which VAT invoices you need to support a fuel input tax claim, including fuel bought by employees on your behalf. A receipt photo attached to the fill record is far easier to find than a carrier bag of paper in the cab door.

How to calculate MPG per truck properly

Do not divide one fill's litres by the miles since the last fill unless both fills were brimmed. A half tank on Monday and a full tank on Wednesday will give you nonsense.

Use the full-to-full method. Pick two fills where the tank was filled to the top. Add up the miles between them and every litre put in after the first full fill, up to and including the second. Then convert litres to gallons. The UK gallon is 4.54609 litres, as defined in Schedule 1 to the Weights and Measures Act 1985.

Worked example (fictional vehicle and figures):

Miles from the first full fill to the second: 413,520 minus 412,300 = 1,220 miles. Litres used: 210 + 330 = 540 litres, which is 540 ÷ 4.54609 = 118.8 gallons. MPG: 1,220 ÷ 118.8 = about 10.3 mpg.

The first 380 litres are left out because they refilled fuel burned before Monday. Run this over a month rather than a week and the figure settles down.

Compare each truck with itself first

A tractor unit on a night trunk between two distribution centres will always beat a rigid doing multi-drop in town. Comparing them tells you nothing. The useful comparisons are:

1. Each vehicle against its own average over the previous three months
2. Vehicles of the same type on the same kind of work
3. The same vehicle with different drivers

Payload matters, so does the trailer. A curtainsider with a damaged roof or a fridge trailer with the unit running all night will drag the figure down. That is why the trailer number belongs on every fill record.

Outliers worth a phone call

Set some simple house rules and check them weekly. Ours, as an example, would be:

• A single fill larger than the tank capacity of the vehicle recorded
• Two fills on the same vehicle within a few hours with little mileage between them
• An odometer reading lower than the previous fill
• Fills at a site or time that does not match the job sheet for that day
• A vehicle whose monthly MPG drops by more than 10% against its own three-month average

Most of these turn out to be honest mistakes: the wrong registration keyed in, a driver in a spare truck, a typo on the odometer. Fix the record and move on. If the same pattern keeps returning on one card or one vehicle, then it needs a proper look.

A sudden MPG drop with no change of work or driver is often mechanical. Dragging brakes, underinflated tyres, a leaking air system that keeps the compressor working, or an injector fault can all show up in the fuel log before anyone reports a defect. Pass it to your workshop with the dates, and check it against recent walkaround and defect records.

Idling, driving style and drivers

Idling is the easy win. Regulation 98 of the Road Vehicles (Construction and Use) Regulations 1986 requires the driver to stop the engine when the vehicle is stationary, so far as necessary to prevent noise or exhaust emissions, with exceptions such as being stationary in traffic. Long idling while waiting at a gatehouse for a booking-in slot, or running the engine for cab heat on a cold morning in the yard, both show up in the fuel figures.

Driving style is harder. Harsh acceleration, late braking and cruising at the limiter on every motorway all cost fuel. How you raise it matters more than the numbers:

• Share the vehicle's figures with the driver, not a league table pinned to the canteen wall
• Compare like with like: same vehicle type, similar work
• Ask what was different that week before assuming anything: diversions, a heavy load, a stuck trailer brake
• Recognise improvement as quickly as you query a bad week

Drivers who see that the office understands their job are far more likely to give you the detail that explains an outlier.

A weekly fuel log routine for the office

This takes about 30 minutes for a small fleet:

1. Monday morning: check last week's fills are all in, each with a receipt photo and odometer reading.
2. Chase gaps: any vehicle that ran all week with no recorded fill needs a call.
3. Run the outlier rules above and note anything to follow up.
4. Update MPG per vehicle using full-to-full fills.
5. Pass mechanical suspicions to the workshop with dates and vehicle details.
6. Once a month: total litres and spend per vehicle, and feed that into your costings and your fuel surcharge formula.

If you already hold a monthly review, fuel cost per mile fits naturally alongside the measures in our monthly haulage operations review. For wider savings beyond the log itself, our guide to controlling fuel and running costs covers purchasing, tyres and route discipline.

Frequently asked questions

What is a good MPG for an HGV?

There is no single figure that fits every fleet. MPG depends on vehicle type, payload, trailer, terrain and the work itself. The most useful benchmark is each vehicle's own average over recent months on similar work.

Should drivers record fuel or should the office?

The driver should record the fill at the pump, because only they can read the odometer and confirm a full tank at that moment. The office should then check, complete and reconcile the record each week.

How do I record fuel bought at the yard bunker?

Treat it like any other fill: vehicle, driver, odometer, litres and whether the tank was brimmed. Reconcile total bunker litres issued against deliveries into the tank each month, so losses do not go unnoticed.

Do I need to keep fuel receipts?

For VAT purposes, HMRC's notice 700/64 explains what VAT invoices you need to support a fuel claim. Keeping a photo of each receipt with the fill record also makes driver queries and fuel card disputes much quicker to settle.

Where HauliK fits

HauliK's Fleet plan includes fuel logs recorded against each vehicle, alongside jobs, maintenance and PMI records and driver timesheets. Fills and defects sit in the same system as the vehicle, so a fuel drop can be checked against recent defect reports without hunting through separate spreadsheets. HauliK does not connect to fuel cards or telematics, so the fill details are entered rather than imported automatically.

The Pro plan adds CSV exports of reports such as vehicle history, defects and maintenance, which helps when a fuel question turns into a workshop question. See what each plan includes, and test the fuel log with your own vehicles during the 14-day free trial, no card needed.