Fleet Cost Formulas, Written Out in Full
Fleet costing is not difficult arithmetic. It goes wrong because a cost lands in the wrong bucket, or because a denominator quietly excludes the empty kilometres. Every formula here is written out so you can see exactly what sits on each side of the divide.
Two people can calculate cost per kilometre for the same fleet, in the same month, and land four cents apart. Neither has made a mistake. One included the vehicles parked awaiting disposal and one did not. One counted empty running in the distance and one counted only revenue kilometres. The formula was never the problem.
So this sheet writes both sides out. Where a denominator has a choice in it, the row says which choice it makes. Where a figure double-counts if you are careless, the row says where. Copy them into a spreadsheet if you like — the value is not the algebra, it is agreeing once what goes into each term and then not moving it.
One rule runs through all of it: keep every input in the same currency and the same period, and never mix a monthly cost with an annual distance. That single error has produced more confidently wrong fleet numbers than everything else on this page combined.
Cost per unit of work
| Figure | What it answers | Formula |
|---|---|---|
| Operating cost per kilometre | The workhorse. Everything the fleet spent, spread across everything it ran, including the empty kilometres. | (Fixed cost + Variable cost) ÷ Kilometres run in the same period |
| Operating cost per hour | The right unit when the asset earns by time rather than distance: plant, cranes, refuse vehicles. | (Fixed cost + Variable cost) ÷ Engine hours in the period |
| Cost per trip | A fair average across the period. Avoids the double-counting you get from allocating fixed cost by hand. | Total operating cost for the period ÷ Trips completed in the period |
| Cost per drop | The figure a multi-drop operation actually prices against. Count successful drops, not attempted ones. | Route cost ÷ Successful drops on that route |
| Cost per tonne-kilometre | Normalises for load. The only per-unit figure that compares a full run fairly against a half-empty one. | Total operating cost ÷ (Tonnes carried × Kilometres those tonnes moved) |
| Revenue per kilometre | What a kilometre earns. Divide by all kilometres, or the figure flatters you by hiding the empty legs. | Billed revenue ÷ All kilometres run, loaded and empty |
Ownership and depreciation
| Figure | What it answers | Formula |
|---|---|---|
| Straight-line depreciation | The annual cost of owning the asset. Simple, and wrong in year one, where real depreciation is steepest. | (Purchase price − Expected resale) ÷ Holding period in years |
| Depreciation per kilometre | Converts ownership into the same unit as fuel, which is the only way to compare the two honestly. | (Purchase price − Expected resale) ÷ Distance run across the holding period |
| Residual value percentage | How much of the purchase price you get back. The number a lease is quietly priced on. | (Resale value ÷ Purchase price) × 100 |
| Annual cost of ownership | The all-in yearly figure per vehicle. Add finance only when you want the fully loaded version. | Depreciation per year + Finance + Insurance and tax + Maintenance + Fuel |
| Cost of keeping one more year | The keep-or-replace question. Depreciation is the term people forget, because no invoice ever arrives for it. | (Value today − Value in twelve months) + Maintenance + Fuel + (Days off road × Margin per day) |
| Downtime cost | What an off-road day really costs. Hire and lost margin both belong here, and usually only one gets counted. | Days off road × (Margin the vehicle earns per day + Hire cost per day) |
Fuel arithmetic
| Figure | What it answers | Formula |
|---|---|---|
| Consumption in litres per 100 km | The base engineering figure. Lower is better, which is the opposite of the mpg instinct half your team has. | (Litres ÷ Kilometres) × 100 |
| US mpg to litres per 100 km | For fleets reading American figures. Establish which gallon you are holding before converting anything. | 235.215 ÷ miles per US gallon |
| Imperial mpg to litres per 100 km | The UK gallon is larger, so the constant differs. The wrong one flatters consumption by roughly a fifth. | 282.481 ÷ miles per imperial gallon |
| Fuel cost per kilometre | Separates the price you cannot control from the consumption you can. | (Litres per 100 km ÷ 100) × Price per litre |
| Idle fuel cost | Fuel burned producing nothing. Never appears in a per-kilometre rate, because no kilometres happened. | Idle hours × Litres burned per idle hour × Price per litre |
| Fuel variance | What the tank cannot account for. Anything materially away from zero is a measurement problem or a loss. | Litres purchased − Litres burned − (Closing tank level − Opening tank level) |
Break-even and margin
| Figure | What it answers | Formula |
|---|---|---|
| Variable cost per kilometre | Cost that only exists when the wheels turn. Salaried drivers do not belong in this term. | Fuel + Driver overtime + Maintenance + Tyres + Tolls, each per kilometre |
| Contribution per kilometre | What each kilometre leaves behind for fixed costs. Negative means running further makes it worse. | Revenue per kilometre − Variable cost per kilometre |
| Break-even distance | The distance below which no amount of good management produces a profit. | Fixed cost for the period ÷ Contribution per kilometre |
| Margin of safety | How much volume you could lose before the fleet stops covering its base. The number to watch monthly. | ((Distance run − Break-even distance) ÷ Distance run) × 100 |
| Operating ratio | Expenses as a share of revenue. Under 100 means the operation is profitable before financing. | (Operating expenses ÷ Operating revenue) × 100 |
| Rate needed at current distance | The rate card test. Below this figure, at this volume, the fleet does not cover itself. | Variable cost per kilometre + (Fixed cost ÷ Distance run) |
Frequently asked questions
Fixed, in most employed fleets, because you pay them whether the work turned up or not. Only the part that genuinely varies with running — overtime, night rates, agency cover, subsistence — belongs in a per-kilometre figure. Treating all wages as variable is the single most common way a break-even distance ends up looking far lower than it is, and it flatters exactly the marginal contract you should be refusing.
Because cost per kilometre punishes the loaded run. A vehicle carrying twenty-six tonnes burns more fuel and wears more brake than the same vehicle carrying eight, so it looks worse per kilometre while doing three times the work. Tonne-kilometres put the work in the denominator where it belongs. The catch is that you need real weights, and a fleet that cubes out before it weighs out should use cubic metres instead.
Ask, because both constants are on this sheet and they sit about twenty percent apart. Figures from a North American source or a US-built vehicle are almost certainly the US gallon, so the constant is 235.215. UK and Irish operations quoting mpg out of habit are usually on the imperial gallon at 282.481. Converting with the wrong one produces a consumption figure that errs in the comfortable direction, which is precisely why nobody catches it.
It will not be zero, and a system reporting zero is rounding something away. Tank sensors infer volume from level through a calibration table, tanks read best in the middle of their range, and fuel expands as it warms. Over a shift the residual should be small and unsigned — noise, not drift. What matters is the pattern: a variance that is consistently negative on one vehicle, one bowser, or one shift is not measurement error. Compare full-to-full cycles when you need precision.
Actuals, with one exception. Budget numbers tell you what you intended, which is useful for a variance conversation and useless for a decision about a vehicle. The exception is forward-looking arithmetic: the cost of keeping one more year needs an estimate of next year's maintenance, and there is no actual for a year that has not happened. Where you must estimate, run it twice at the optimistic and pessimistic ends. If the answer holds, the decision is safe.
See these metrics on your own fleet
Fleet Analytics Software reports every one of these numbers from live operational data.