Fleet Size Calculator
Fleets rarely get sized. They accumulate. A vehicle is added for a contract, kept when the contract ends, and eleven years later nobody can say why the number is what it is. This calculator works the number out from the workload instead.
Your numbers
Drops, collections or service calls on an ordinary day, not your best day.
Arrival to departure: waiting, handling, paperwork and the signature.
Average drive time from one job to the next, including parking.
Clock on to clock off for one vehicle. Double-shifted? Enter the combined hours.
What is left after breaks, briefing, checks, fuelling and the run out from depot.
How much busier your regular peak is than an ordinary day.
Share of the fleet fit to work on any given morning. Service, damage, VOR.
Result
Fleet required
40 vehicles
Vehicles needed to cover the peak day at your stated availability.
- Vehicles working at peak
- 35 vehicles
- Vehicles working on an average day
- 30 vehicles
- Spare vehicles
- 5.1 vehicles
- Peak demand
- 14,688 minutes/day
- Productive minutes per vehicle
- 421 minutes/shift
- Minutes per job
- 36.0 minutes
The formula
- Minutes per job = Time at the job + Travel between jobs
- Average demand = Jobs per day × Minutes per job
- Peak demand = Average demand × (1 + Peak day above average ÷ 100)
- Productive minutes per vehicle = Shift length × 60 × (Productive share of the shift ÷ 100)
- Vehicles working at peak = Peak demand ÷ Productive minutes per vehicle, shown rounded up
- Fleet required = Vehicles working at peak ÷ (Vehicle availability ÷ 100), rounded up
- Vehicles working on an average day = Average demand ÷ Productive minutes per vehicle, rounded up
- Spare vehicles = Fleet required − Vehicles working at peak, before rounding, never below zero
Assumptions and limits
- Demand is treated as a pool of minutes that any vehicle can absorb. Real work has geography, time windows and vehicle types, and every one of those constraints pushes the true requirement upwards.
- Every vehicle is assumed interchangeable. If half the fleet is tail-lift only and half the jobs need one, size the two groups separately or the answer is meaningless.
- Peak is modelled as one uplift percentage. A fleet with a genuine seasonal peak should not own for December. Size for the ordinary year and hire for the spike.
- Availability is an average, and averages hide correlation. Vehicles of the same age tend to fail in the same season, so the morning you are short is worse than this figure suggests.
- No allowance is made for the driver. A vehicle without anyone to drive it is not capacity, and driver availability is usually the tighter constraint.
- The output is a planning number for a conversation, not an order. Round it against contract terms, lead times and what your depot can physically park.
Fleets are inherited, not designed
Ask why a fleet has sixty-one vehicles and the honest answer is history. Fifty-two came with the business. Six arrived for a contract in 2019. Three were bought because a depot manager kept complaining, and the complaining stopped, so nobody revisited it. The number is the residue of decisions, not the output of one.
That would be fine if workloads stood still. They do not. Drop density changes, time windows tighten, a customer moves their distribution centre thirty kilometres, and the fleet that was correctly sized for the old pattern is quietly wrong for the new one. Usually too large, occasionally too small, always in a way nobody has measured.
Where the sizing goes wrong: the productive share
The field people get wrong is the productive share of the shift, and they get it wrong in the same direction every time. A nine-hour shift is not nine hours of work. There is the walkaround, the briefing, the run out from depot to the first job and back from the last, the statutory break, fuelling, the queue at the gate, and the twenty minutes at the end that nobody has ever accounted for.
Assume a full shift is productive and the model hands you a fleet that cannot do the work, and then a depot that quietly fixes it with overtime and hire vehicles. The number will look efficient in a report and will not survive a Tuesday.
If you have telematics, do not estimate this field. Take actual engine-on time against paid time for a normal month. Most fleets are surprised, and the surprise is worth more than the calculator.
Spare vehicles are not waste
The availability field is what turns a peak requirement into a fleet size, and the difference between those two figures is your spares. It is tempting to read that gap as slack to be removed. It is not slack. It is the reason a service booking does not become a failed delivery.
A fleet sized exactly to its peak with no availability allowance is a fleet where every routine service is a crisis and every damaged wing mirror is an operational decision. The cost of that shows up as hire, overtime and missed windows, all of it charged somewhere other than the fleet budget, which is precisely why cutting spares looks like a saving on paper.
The honest question is not whether to hold spares. It is whether to hold them as owned vehicles or as a hire agreement, and that turns on how predictable your peak is and how quickly your supplier can deliver.
Frequently asked questions
Measure it rather than guess it. Count, for one ordinary month, how many vehicles were fit to work each morning against how many you own, and average it. Guessing produces a flattering number because the vehicle that has been off the road for six weeks stops registering as part of the fleet in people's heads. If you genuinely have no data, run the calculator across a range and look at how much the answer moves.
Possibly, but check the constraints the model ignores first. Vehicle types that cannot substitute for each other, depots that cannot share, time windows that force two vehicles into the same hour, and jobs that need a specific licence or a specific driver. Those constraints are real capacity requirements, and this model cannot see any of them. Treat the gap as a question to investigate, not a disposal list.
Not with this field. The peak uplift is for the regular rhythm, the Friday that is busier than the Tuesday. A genuine seasonal peak is a different decision: owning vehicles for eight weeks of demand means paying depreciation, insurance and yard space for the other forty-four. Size the fleet for the ordinary year and cover the season with hire, agency drivers or subcontractors, then compare the two costs.
Only if you run it once per group of genuinely interchangeable vehicles. Rigids and artics are not one fleet. A refrigerated body is not a substitute for a curtainsider. Running the numbers across a mixed fleet averages away the constraint that actually determines your size, and the total will come out too low.
Because it deserves its own model, and folding it in here would let you believe the vehicle count is the whole answer. In most fleets the binding constraint is people: licences, hours rules, absence, and how long it takes to hire. Size the vehicles here, then check whether you can crew them. If you cannot, the fleet size question was never the real one.
Stop estimating. Measure it.
Fleet Size Calculator gives you the arithmetic. Fleet Management Software gives you the live numbers from your own fleet.